    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      http://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017package org.apache.commons.collections4.trie;
    018
    019import java.io.IOException;
    020import java.io.ObjectInputStream;
    021import java.io.ObjectOutputStream;
    022import java.util.AbstractCollection;
    023import java.util.AbstractMap;
    024import java.util.AbstractSet;
    025import java.util.Collection;
    026import java.util.Collections;
    027import java.util.Comparator;
    028import java.util.ConcurrentModificationException;
    029import java.util.Iterator;
    030import java.util.Map;
    031import java.util.NoSuchElementException;
    032import java.util.Objects;
    033import java.util.Set;
    034import java.util.SortedMap;
    035
    036import org.apache.commons.collections4.OrderedMapIterator;
    037import org.apache.commons.collections4.Trie;
    038
    039/**
    040 * This class implements the base PATRICIA algorithm and everything that
    041 * is related to the {@link Map} interface.
    042 *
    043 * @param <K> the type of the keys in this map
    044 * @param <V> the type of the values in this map
    045 * @since 4.0
    046 */
    047public abstract class AbstractPatriciaTrie<K, V> extends AbstractBitwiseTrie<K, V> {
    048
    049    /**
    050     * A range view of the {@link org.apache.commons.collections4.Trie}.
    051     */
    052    private abstract class AbstractRangeMap extends AbstractMap<K, V>
    053            implements SortedMap<K, V> {
    054
    055        /** The {@link #entrySet()} view. */
    056        private transient volatile Set<Map.Entry<K, V>> entrySet;
    057
    058        @Override
    059        public Comparator<? super K> comparator() {
    060            return AbstractPatriciaTrie.this.comparator();
    061        }
    062
    063        @Override
    064        public boolean containsKey(final Object key) {
    065            if (!inRange(castKey(key))) {
    066                return false;
    067            }
    068
    069            return AbstractPatriciaTrie.this.containsKey(key);
    070        }
    071
    072        /**
    073         * Creates and returns an {@link #entrySet()} view of the {@link AbstractRangeMap}.
    074         */
    075        protected abstract Set<Map.Entry<K, V>> createEntrySet();
    076
    077        /**
    078         * Creates and returns a sub-range view of the current {@link AbstractRangeMap}.
    079         */
    080        protected abstract SortedMap<K, V> createRangeMap(K fromKey, boolean fromInclusive,
    081                                                          K toKey, boolean toInclusive);
    082
    083        @Override
    084        public Set<Map.Entry<K, V>> entrySet() {
    085            if (entrySet == null) {
    086                entrySet = createEntrySet();
    087            }
    088            return entrySet;
    089        }
    090
    091        @Override
    092        public V get(final Object key) {
    093            if (!inRange(castKey(key))) {
    094                return null;
    095            }
    096
    097            return AbstractPatriciaTrie.this.get(key);
    098        }
    099
    100        /**
    101         * Returns the FROM Key.
    102         */
    103        protected abstract K getFromKey();
    104
    105        /**
    106         * Returns the TO Key.
    107         */
    108        protected abstract K getToKey();
    109
    110        @Override
    111        public SortedMap<K, V> headMap(final K toKey) {
    112            if (!inRange2(toKey)) {
    113                throw new IllegalArgumentException("ToKey is out of range: " + toKey);
    114            }
    115            return createRangeMap(getFromKey(), isFromInclusive(), toKey, isToInclusive());
    116        }
    117
    118        /**
    119         * Returns true if the provided key is in the FROM range of the {@link AbstractRangeMap}.
    120         */
    121        protected boolean inFromRange(final K key, final boolean forceInclusive) {
    122            final K fromKey = getFromKey();
    123            final boolean fromInclusive = isFromInclusive();
    124
    125            final int ret = getKeyAnalyzer().compare(key, fromKey);
    126            if (fromInclusive || forceInclusive) {
    127                return ret >= 0;
    128            }
    129            return ret > 0;
    130        }
    131
    132        /**
    133         * Returns true if the provided key is greater than TO and less than FROM.
    134         */
    135        protected boolean inRange(final K key) {
    136            final K fromKey = getFromKey();
    137            final K toKey = getToKey();
    138
    139            return (fromKey == null || inFromRange(key, false)) && (toKey == null || inToRange(key, false));
    140        }
    141
    142        /**
    143         * This form allows the high endpoint (as well as all legit keys).
    144         */
    145        protected boolean inRange2(final K key) {
    146            final K fromKey = getFromKey();
    147            final K toKey = getToKey();
    148
    149            return (fromKey == null || inFromRange(key, false)) && (toKey == null || inToRange(key, true));
    150        }
    151
    152        /**
    153         * Returns true if the provided key is in the TO range of the {@link AbstractRangeMap}.
    154         */
    155        protected boolean inToRange(final K key, final boolean forceInclusive) {
    156            final K toKey = getToKey();
    157            final boolean toInclusive = isToInclusive();
    158
    159            final int ret = getKeyAnalyzer().compare(key, toKey);
    160            if (toInclusive || forceInclusive) {
    161                return ret <= 0;
    162            }
    163            return ret < 0;
    164        }
    165
    166        /**
    167         * Whether or not the {@link #getFromKey()} is in the range.
    168         */
    169        protected abstract boolean isFromInclusive();
    170
    171        /**
    172         * Whether or not the {@link #getToKey()} is in the range.
    173         */
    174        protected abstract boolean isToInclusive();
    175
    176        @Override
    177        public V put(final K key, final V value) {
    178            if (!inRange(key)) {
    179                throw new IllegalArgumentException("Key is out of range: " + key);
    180            }
    181            return AbstractPatriciaTrie.this.put(key, value);
    182        }
    183
    184        @Override
    185        public V remove(final Object key) {
    186            if (!inRange(castKey(key))) {
    187                return null;
    188            }
    189
    190            return AbstractPatriciaTrie.this.remove(key);
    191        }
    192
    193        @Override
    194        public SortedMap<K, V> subMap(final K fromKey, final K toKey) {
    195            if (!inRange2(fromKey)) {
    196                throw new IllegalArgumentException("FromKey is out of range: " + fromKey);
    197            }
    198
    199            if (!inRange2(toKey)) {
    200                throw new IllegalArgumentException("ToKey is out of range: " + toKey);
    201            }
    202
    203            return createRangeMap(fromKey, isFromInclusive(), toKey, isToInclusive());
    204        }
    205
    206        @Override
    207        public SortedMap<K, V> tailMap(final K fromKey) {
    208            if (!inRange2(fromKey)) {
    209                throw new IllegalArgumentException("FromKey is out of range: " + fromKey);
    210            }
    211            return createRangeMap(fromKey, isFromInclusive(), getToKey(), isToInclusive());
    212        }
    213    }
    214
    215    /**
    216     * An iterator for the entries.
    217     */
    218    abstract class AbstractTrieIterator<E> implements Iterator<E> {
    219
    220        /** For fast-fail. */
    221        protected int expectedModCount = AbstractPatriciaTrie.this.modCount;
    222
    223        protected TrieEntry<K, V> next; // the next node to return
    224        protected TrieEntry<K, V> current; // the current entry we're on
    225
    226        /**
    227         * Starts iteration from the root.
    228         */
    229        protected AbstractTrieIterator() {
    230            next = AbstractPatriciaTrie.this.nextEntry(null);
    231        }
    232
    233        /**
    234         * Starts iteration at the given entry.
    235         */
    236        protected AbstractTrieIterator(final TrieEntry<K, V> firstEntry) {
    237            next = firstEntry;
    238        }
    239
    240        /**
    241         * @see PatriciaTrie#nextEntry(TrieEntry)
    242         */
    243        protected TrieEntry<K, V> findNext(final TrieEntry<K, V> prior) {
    244            return AbstractPatriciaTrie.this.nextEntry(prior);
    245        }
    246
    247        @Override
    248        public boolean hasNext() {
    249            return next != null;
    250        }
    251
    252        /**
    253         * Returns the next {@link TrieEntry}.
    254         */
    255        protected TrieEntry<K, V> nextEntry() {
    256            if (expectedModCount != AbstractPatriciaTrie.this.modCount) {
    257                throw new ConcurrentModificationException();
    258            }
    259
    260            final TrieEntry<K, V> e = next;
    261            if (e == null) {
    262                throw new NoSuchElementException();
    263            }
    264
    265            next = findNext(e);
    266            current = e;
    267            return e;
    268        }
    269
    270        @Override
    271        public void remove() {
    272            if (current == null) {
    273                throw new IllegalStateException();
    274            }
    275
    276            if (expectedModCount != AbstractPatriciaTrie.this.modCount) {
    277                throw new ConcurrentModificationException();
    278            }
    279
    280            final TrieEntry<K, V> node = current;
    281            current = null;
    282            AbstractPatriciaTrie.this.removeEntry(node);
    283
    284            expectedModCount = AbstractPatriciaTrie.this.modCount;
    285        }
    286    }
    287
    288    /**
    289     * This is an entry set view of the {@link org.apache.commons.collections4.Trie} as returned by {@link Map#entrySet()}.
    290     */
    291    private final class EntrySet extends AbstractSet<Map.Entry<K, V>> {
    292
    293        /**
    294         * An {@link Iterator} that returns {@link Entry} Objects.
    295         */
    296        private final class EntryIterator extends AbstractTrieIterator<Map.Entry<K, V>> {
    297            @Override
    298            public Map.Entry<K, V> next() {
    299                return nextEntry();
    300            }
    301        }
    302
    303        @Override
    304        public void clear() {
    305            AbstractPatriciaTrie.this.clear();
    306        }
    307
    308        @Override
    309        public boolean contains(final Object o) {
    310            if (!(o instanceof Map.Entry)) {
    311                return false;
    312            }
    313
    314            final TrieEntry<K, V> candidate = getEntry(((Map.Entry<?, ?>) o).getKey());
    315            return candidate != null && candidate.equals(o);
    316        }
    317
    318        @Override
    319        public Iterator<Map.Entry<K, V>> iterator() {
    320            return new EntryIterator();
    321        }
    322
    323        @Override
    324        public boolean remove(final Object obj) {
    325            if (!(obj instanceof Map.Entry)) {
    326                return false;
    327            }
    328            if (!contains(obj)) {
    329                return false;
    330            }
    331            final Map.Entry<?, ?> entry = (Map.Entry<?, ?>) obj;
    332            AbstractPatriciaTrie.this.remove(entry.getKey());
    333            return true;
    334        }
    335
    336        @Override
    337        public int size() {
    338            return AbstractPatriciaTrie.this.size();
    339        }
    340    }
    341    /**
    342     * This is a key set view of the {@link org.apache.commons.collections4.Trie} as returned by {@link Map#keySet()}.
    343     */
    344    private final class KeySet extends AbstractSet<K> {
    345
    346        /**
    347         * An {@link Iterator} that returns Key Objects.
    348         */
    349        private final class KeyIterator extends AbstractTrieIterator<K> {
    350            @Override
    351            public K next() {
    352                return nextEntry().getKey();
    353            }
    354        }
    355
    356        @Override
    357        public void clear() {
    358            AbstractPatriciaTrie.this.clear();
    359        }
    360
    361        @Override
    362        public boolean contains(final Object o) {
    363            return containsKey(o);
    364        }
    365
    366        @Override
    367        public Iterator<K> iterator() {
    368            return new KeyIterator();
    369        }
    370
    371        @Override
    372        public boolean remove(final Object o) {
    373            final int size = size();
    374            AbstractPatriciaTrie.this.remove(o);
    375            return size != size();
    376        }
    377
    378        @Override
    379        public int size() {
    380            return AbstractPatriciaTrie.this.size();
    381        }
    382    }
    383    /**
    384     * A prefix {@link RangeEntrySet} view of the {@link org.apache.commons.collections4.Trie}.
    385     */
    386    private final class PrefixRangeEntrySet extends RangeEntrySet {
    387
    388        /**
    389         * An {@link Iterator} for iterating over a prefix search.
    390         */
    391        private final class EntryIterator extends AbstractTrieIterator<Map.Entry<K, V>> {
    392
    393            // values to reset the subtree if we remove it.
    394            private final K prefix;
    395            private final int offset;
    396            private final int lengthInBits;
    397            private boolean lastOne;
    398
    399            private TrieEntry<K, V> subtree; // the subtree to search within
    400
    401            /**
    402             * Starts iteration at the given entry &amp; search only
    403             * within the given subtree.
    404             */
    405            EntryIterator(final TrieEntry<K, V> startScan, final K prefix,
    406                    final int offset, final int lengthInBits) {
    407                subtree = startScan;
    408                next = AbstractPatriciaTrie.this.followLeft(startScan);
    409                this.prefix = prefix;
    410                this.offset = offset;
    411                this.lengthInBits = lengthInBits;
    412            }
    413
    414            @Override
    415            protected TrieEntry<K, V> findNext(final TrieEntry<K, V> prior) {
    416                return AbstractPatriciaTrie.this.nextEntryInSubtree(prior, subtree);
    417            }
    418
    419            @Override
    420            public Map.Entry<K, V> next() {
    421                final Map.Entry<K, V> entry = nextEntry();
    422                if (lastOne) {
    423                    next = null;
    424                }
    425                return entry;
    426            }
    427
    428            @Override
    429            public void remove() {
    430                // If the current entry we're removing is the subtree
    431                // then we need to find a new subtree parent.
    432                boolean needsFixing = false;
    433                final int bitIdx = subtree.bitIndex;
    434                if (current == subtree) {
    435                    needsFixing = true;
    436                }
    437
    438                super.remove();
    439
    440                // If the subtree changed its bitIndex or we
    441                // removed the old subtree, get a new one.
    442                if (bitIdx != subtree.bitIndex || needsFixing) {
    443                    subtree = subtree(prefix, offset, lengthInBits);
    444                }
    445
    446                // If the subtree's bitIndex is less than the
    447                // length of our prefix, it's the last item
    448                // in the prefix tree.
    449                if (lengthInBits >= subtree.bitIndex) {
    450                    lastOne = true;
    451                }
    452            }
    453        }
    454
    455        /**
    456         * An {@link Iterator} that holds a single {@link TrieEntry}.
    457         */
    458        private final class SingletonIterator implements Iterator<Map.Entry<K, V>> {
    459
    460            private final TrieEntry<K, V> entry;
    461
    462            private int hit;
    463
    464            SingletonIterator(final TrieEntry<K, V> entry) {
    465                this.entry = entry;
    466            }
    467
    468            @Override
    469            public boolean hasNext() {
    470                return hit == 0;
    471            }
    472
    473            @Override
    474            public Map.Entry<K, V> next() {
    475                if (hit != 0) {
    476                    throw new NoSuchElementException();
    477                }
    478
    479                ++hit;
    480                return entry;
    481            }
    482
    483            @Override
    484            public void remove() {
    485                if (hit != 1) {
    486                    throw new IllegalStateException();
    487                }
    488
    489                ++hit;
    490                AbstractPatriciaTrie.this.removeEntry(entry);
    491            }
    492        }
    493
    494        private final PrefixRangeMap delegate;
    495
    496        private TrieEntry<K, V> prefixStart;
    497
    498        private int expectedModCount;
    499
    500        /**
    501         * Creates a {@link PrefixRangeEntrySet}.
    502         */
    503        PrefixRangeEntrySet(final PrefixRangeMap delegate) {
    504            super(delegate);
    505            this.delegate = delegate;
    506        }
    507
    508        @Override
    509        public Iterator<Map.Entry<K, V>> iterator() {
    510            if (AbstractPatriciaTrie.this.modCount != expectedModCount) {
    511                prefixStart = subtree(delegate.prefix, delegate.offsetInBits, delegate.lengthInBits);
    512                expectedModCount = AbstractPatriciaTrie.this.modCount;
    513            }
    514
    515            if (prefixStart == null) {
    516                final Set<Map.Entry<K, V>> empty = Collections.emptySet();
    517                return empty.iterator();
    518            }
    519            if (delegate.lengthInBits > prefixStart.bitIndex) {
    520                return new SingletonIterator(prefixStart);
    521            }
    522            return new EntryIterator(prefixStart, delegate.prefix, delegate.offsetInBits, delegate.lengthInBits);
    523        }
    524
    525        @Override
    526        public int size() {
    527            return delegate.fixup();
    528        }
    529    }
    530
    531    /**
    532     * A submap used for prefix views over the {@link org.apache.commons.collections4.Trie}.
    533     */
    534    private final class PrefixRangeMap extends AbstractRangeMap {
    535
    536        private final K prefix;
    537
    538        private final int offsetInBits;
    539
    540        private final int lengthInBits;
    541
    542        private K fromKey;
    543
    544        private K toKey;
    545
    546        private transient int expectedModCount;
    547
    548        private int size = -1;
    549
    550        /**
    551         * Creates a {@link PrefixRangeMap}.
    552         */
    553        private PrefixRangeMap(final K prefix, final int offsetInBits, final int lengthInBits) {
    554            this.prefix = prefix;
    555            this.offsetInBits = offsetInBits;
    556            this.lengthInBits = lengthInBits;
    557        }
    558
    559        @Override
    560        public void clear() {
    561            final Iterator<Map.Entry<K, V>> it = AbstractPatriciaTrie.this.entrySet().iterator();
    562            final Set<K> currentKeys = keySet();
    563            while (it.hasNext()) {
    564                if (currentKeys.contains(it.next().getKey())) {
    565                    it.remove();
    566                }
    567            }
    568        }
    569
    570        @Override
    571        protected Set<Map.Entry<K, V>> createEntrySet() {
    572            return new PrefixRangeEntrySet(this);
    573        }
    574
    575        @Override
    576        protected SortedMap<K, V> createRangeMap(final K fromKey, final boolean fromInclusive,
    577                                                 final K toKey, final boolean toInclusive) {
    578            return new RangeEntryMap(fromKey, fromInclusive, toKey, toInclusive);
    579        }
    580
    581        @Override
    582        public K firstKey() {
    583            fixup();
    584
    585            Map.Entry<K, V> e = null;
    586            if (fromKey == null) {
    587                e = firstEntry();
    588            } else {
    589                e = higherEntry(fromKey);
    590            }
    591
    592            final K first = e != null ? e.getKey() : null;
    593            if (e == null || !getKeyAnalyzer().isPrefix(prefix, offsetInBits, lengthInBits, first)) {
    594                throw new NoSuchElementException();
    595            }
    596
    597            return first;
    598        }
    599
    600        /**
    601         * This method does two things. It determines the FROM
    602         * and TO range of the {@link PrefixRangeMap} and the number
    603         * of elements in the range. This method must be called every
    604         * time the {@link org.apache.commons.collections4.Trie} has changed.
    605         */
    606        private int fixup() {
    607            // The trie has changed since we last found our toKey / fromKey
    608            if (size == - 1 || AbstractPatriciaTrie.this.modCount != expectedModCount) {
    609                final Iterator<Map.Entry<K, V>> it = super.entrySet().iterator();
    610                size = 0;
    611
    612                Map.Entry<K, V> entry = null;
    613                if (it.hasNext()) {
    614                    entry = it.next();
    615                    size = 1;
    616                }
    617
    618                fromKey = entry == null ? null : entry.getKey();
    619                if (fromKey != null) {
    620                    final TrieEntry<K, V> prior = previousEntry((TrieEntry<K, V>) entry);
    621                    fromKey = prior == null ? null : prior.getKey();
    622                }
    623
    624                toKey = fromKey;
    625
    626                while (it.hasNext()) {
    627                    ++size;
    628                    entry = it.next();
    629                }
    630
    631                toKey = entry == null ? null : entry.getKey();
    632
    633                if (toKey != null) {
    634                    entry = nextEntry((TrieEntry<K, V>) entry);
    635                    toKey = entry == null ? null : entry.getKey();
    636                }
    637
    638                expectedModCount = AbstractPatriciaTrie.this.modCount;
    639            }
    640
    641            return size;
    642        }
    643
    644        @Override
    645        public K getFromKey() {
    646            return fromKey;
    647        }
    648
    649        @Override
    650        public K getToKey() {
    651            return toKey;
    652        }
    653
    654        /**
    655         * Returns true if the provided Key is in the FROM range of the {@link PrefixRangeMap}.
    656         */
    657        @Override
    658        protected boolean inFromRange(final K key, final boolean forceInclusive) {
    659            return getKeyAnalyzer().isPrefix(prefix, offsetInBits, lengthInBits, key);
    660        }
    661
    662        /**
    663         * Returns true if this {@link PrefixRangeMap}'s key is a prefix of the provided key.
    664         */
    665        @Override
    666        protected boolean inRange(final K key) {
    667            return getKeyAnalyzer().isPrefix(prefix, offsetInBits, lengthInBits, key);
    668        }
    669
    670        /**
    671         * Same as {@link #inRange(Object)}.
    672         */
    673        @Override
    674        protected boolean inRange2(final K key) {
    675            return inRange(key);
    676        }
    677
    678        /**
    679         * Returns true if the provided Key is in the TO range of the {@link PrefixRangeMap}.
    680         */
    681        @Override
    682        protected boolean inToRange(final K key, final boolean forceInclusive) {
    683            return getKeyAnalyzer().isPrefix(prefix, offsetInBits, lengthInBits, key);
    684        }
    685
    686        @Override
    687        public boolean isFromInclusive() {
    688            return false;
    689        }
    690
    691        @Override
    692        public boolean isToInclusive() {
    693            return false;
    694        }
    695
    696        @Override
    697        public K lastKey() {
    698            fixup();
    699
    700            Map.Entry<K, V> e = null;
    701            if (toKey == null) {
    702                e = lastEntry();
    703            } else {
    704                e = lowerEntry(toKey);
    705            }
    706
    707            final K last = e != null ? e.getKey() : null;
    708            if (e == null || !getKeyAnalyzer().isPrefix(prefix, offsetInBits, lengthInBits, last)) {
    709                throw new NoSuchElementException();
    710            }
    711
    712            return last;
    713        }
    714    }
    715
    716    /**
    717     * A {@link AbstractRangeMap} that deals with {@link Entry}s.
    718     */
    719    private final class RangeEntryMap extends AbstractRangeMap {
    720
    721        /** The key to start from, null if the beginning. */
    722        private final K fromKey;
    723
    724        /** The key to end at, null if till the end. */
    725        private final K toKey;
    726
    727        /** Whether or not the 'from' is inclusive. */
    728        private final boolean fromInclusive;
    729
    730        /** Whether or not the 'to' is inclusive. */
    731        private final boolean toInclusive;
    732
    733        /**
    734         * Creates a {@link RangeEntryMap}.
    735         */
    736        protected RangeEntryMap(final K fromKey, final boolean fromInclusive,
    737                                final K toKey, final boolean toInclusive) {
    738
    739            if (fromKey == null && toKey == null) {
    740                throw new IllegalArgumentException("must have a from or to!");
    741            }
    742
    743            if (fromKey != null && toKey != null && getKeyAnalyzer().compare(fromKey, toKey) > 0) {
    744                throw new IllegalArgumentException("fromKey > toKey");
    745            }
    746
    747            this.fromKey = fromKey;
    748            this.fromInclusive = fromInclusive;
    749            this.toKey = toKey;
    750            this.toInclusive = toInclusive;
    751        }
    752
    753        /**
    754         * Creates a {@link RangeEntryMap} with the fromKey included and
    755         * the toKey excluded from the range.
    756         */
    757        protected RangeEntryMap(final K fromKey, final K toKey) {
    758            this(fromKey, true, toKey, false);
    759        }
    760
    761        @Override
    762        protected Set<Entry<K, V>> createEntrySet() {
    763            return new RangeEntrySet(this);
    764        }
    765
    766        @Override
    767        protected SortedMap<K, V> createRangeMap(final K fromKey, final boolean fromInclusive,
    768                                                 final K toKey, final boolean toInclusive) {
    769            return new RangeEntryMap(fromKey, fromInclusive, toKey, toInclusive);
    770        }
    771
    772        @Override
    773        public K firstKey() {
    774            Map.Entry<K, V> e = null;
    775            if (fromKey == null) {
    776                e = firstEntry();
    777            } else {
    778                if (fromInclusive) {
    779                    e = ceilingEntry(fromKey);
    780                } else {
    781                    e = higherEntry(fromKey);
    782                }
    783            }
    784
    785            final K first = e != null ? e.getKey() : null;
    786            if (e == null || toKey != null && !inToRange(first, false)) {
    787                throw new NoSuchElementException();
    788            }
    789            return first;
    790        }
    791
    792        @Override
    793        public K getFromKey() {
    794            return fromKey;
    795        }
    796
    797        @Override
    798        public K getToKey() {
    799            return toKey;
    800        }
    801
    802        @Override
    803        public boolean isFromInclusive() {
    804            return fromInclusive;
    805        }
    806
    807        @Override
    808        public boolean isToInclusive() {
    809            return toInclusive;
    810        }
    811
    812        @Override
    813        public K lastKey() {
    814            final Map.Entry<K, V> e;
    815            if (toKey == null) {
    816                e = lastEntry();
    817            } else {
    818                if (toInclusive) {
    819                    e = floorEntry(toKey);
    820                } else {
    821                    e = lowerEntry(toKey);
    822                }
    823            }
    824
    825            final K last = e != null ? e.getKey() : null;
    826            if (e == null || fromKey != null && !inFromRange(last, false)) {
    827                throw new NoSuchElementException();
    828            }
    829            return last;
    830        }
    831    }
    832
    833    /**
    834     * A {@link Set} view of a {@link AbstractRangeMap}.
    835     */
    836    private class RangeEntrySet extends AbstractSet<Map.Entry<K, V>> {
    837
    838        /**
    839         * An {@link Iterator} for {@link RangeEntrySet}s.
    840         */
    841        private final class EntryIterator extends AbstractTrieIterator<Map.Entry<K, V>> {
    842
    843            private final K excludedKey;
    844
    845            /**
    846             * Creates a {@link EntryIterator}.
    847             */
    848            private EntryIterator(final TrieEntry<K, V> first, final TrieEntry<K, V> last) {
    849                super(first);
    850                this.excludedKey = last != null ? last.getKey() : null;
    851            }
    852
    853            @Override
    854            public boolean hasNext() {
    855                return next != null && !compare(next.key, excludedKey);
    856            }
    857
    858            @Override
    859            public Map.Entry<K, V> next() {
    860                if (next == null || compare(next.key, excludedKey)) {
    861                    throw new NoSuchElementException();
    862                }
    863                return nextEntry();
    864            }
    865        }
    866
    867        private final AbstractRangeMap delegate;
    868
    869        private transient int size = -1;
    870
    871        private transient int expectedModCount;
    872
    873        /**
    874         * Creates a {@link RangeEntrySet}.
    875         */
    876        RangeEntrySet(final AbstractRangeMap delegate) {
    877            this.delegate = Objects.requireNonNull(delegate, "delegate");
    878        }
    879
    880        @SuppressWarnings("unchecked")
    881        @Override
    882        public boolean contains(final Object o) {
    883            if (!(o instanceof Map.Entry)) {
    884                return false;
    885            }
    886
    887            final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
    888            final K key = entry.getKey();
    889            if (!delegate.inRange(key)) {
    890                return false;
    891            }
    892
    893            final TrieEntry<K, V> node = getEntry(key);
    894            return node != null && compare(node.getValue(), entry.getValue());
    895        }
    896
    897        @Override
    898        public boolean isEmpty() {
    899            return !iterator().hasNext();
    900        }
    901
    902        @Override
    903        public Iterator<Map.Entry<K, V>> iterator() {
    904            final K fromKey = delegate.getFromKey();
    905            final K toKey = delegate.getToKey();
    906
    907            TrieEntry<K, V> first = null;
    908            if (fromKey == null) {
    909                first = firstEntry();
    910            } else {
    911                first = ceilingEntry(fromKey);
    912            }
    913
    914            TrieEntry<K, V> last = null;
    915            if (toKey != null) {
    916                last = ceilingEntry(toKey);
    917            }
    918
    919            return new EntryIterator(first, last);
    920        }
    921
    922        @SuppressWarnings("unchecked")
    923        @Override
    924        public boolean remove(final Object o) {
    925            if (!(o instanceof Map.Entry)) {
    926                return false;
    927            }
    928
    929            final Map.Entry<K, V> entry = (Map.Entry<K, V>) o;
    930            final K key = entry.getKey();
    931            if (!delegate.inRange(key)) {
    932                return false;
    933            }
    934
    935            final TrieEntry<K, V> node = getEntry(key);
    936            if (node != null && compare(node.getValue(), entry.getValue())) {
    937                removeEntry(node);
    938                return true;
    939            }
    940            return false;
    941        }
    942
    943        @Override
    944        public int size() {
    945            if (size == -1 || expectedModCount != AbstractPatriciaTrie.this.modCount) {
    946                size = 0;
    947
    948                for (final Iterator<?> it = iterator(); it.hasNext(); it.next()) {
    949                    ++size;
    950                }
    951
    952                expectedModCount = AbstractPatriciaTrie.this.modCount;
    953            }
    954            return size;
    955        }
    956    }
    957
    958    /**
    959     * A {@link Reference} allows us to return something through a Method's
    960     * argument list. An alternative would be to an Array with a length of
    961     * one (1) but that leads to compiler warnings. Computationally and memory
    962     * wise there's no difference (except for the need to load the
    963     * {@link Reference} Class but that happens only once).
    964     */
    965    private static final class Reference<E> {
    966
    967        private E item;
    968
    969        public E get() {
    970            return item;
    971        }
    972
    973        public void set(final E item) {
    974            this.item = item;
    975        }
    976    }
    977
    978    /**
    979     *  A {@link org.apache.commons.collections4.Trie} is a set of {@link TrieEntry} nodes.
    980     */
    981    protected static class TrieEntry<K, V> extends BasicEntry<K, V> {
    982
    983        private static final long serialVersionUID = 4596023148184140013L;
    984
    985        /** The index this entry is comparing. */
    986        protected int bitIndex;
    987
    988        /** The parent of this entry. */
    989        protected TrieEntry<K, V> parent;
    990
    991        /** The left child of this entry. */
    992        protected TrieEntry<K, V> left;
    993
    994        /** The right child of this entry. */
    995        protected TrieEntry<K, V> right;
    996
    997        /** The entry who uplinks to this entry. */
    998        protected TrieEntry<K, V> predecessor;
    999
    1000        public TrieEntry(final K key, final V value, final int bitIndex) {
    1001            super(key, value);
    1002
    1003            this.bitIndex = bitIndex;
    1004
    1005            this.parent = null;
    1006            this.left = this;
    1007            this.right = null;
    1008            this.predecessor = this;
    1009        }
    1010
    1011        /**
    1012         * Whether or not the entry is storing a key.
    1013         * Only the root can potentially be empty, all other
    1014         * nodes must have a key.
    1015         */
    1016        public boolean isEmpty() {
    1017            return key == null;
    1018        }
    1019
    1020        /**
    1021         * Either the left or right child is a loopback.
    1022         */
    1023        public boolean isExternalNode() {
    1024            return !isInternalNode();
    1025        }
    1026
    1027        /**
    1028         * Neither the left nor right child is a loopback.
    1029         */
    1030        public boolean isInternalNode() {
    1031            return left != this && right != this;
    1032        }
    1033
    1034        @Override
    1035        public String toString() {
    1036            final StringBuilder buffer = new StringBuilder();
    1037
    1038            if (bitIndex == -1) {
    1039                buffer.append("RootEntry(");
    1040            } else {
    1041                buffer.append("Entry(");
    1042            }
    1043
    1044            buffer.append("key=").append(getKey()).append(" [").append(bitIndex).append("], ");
    1045            buffer.append("value=").append(getValue()).append(", ");
    1046            //buffer.append("bitIndex=").append(bitIndex).append(", ");
    1047
    1048            if (parent != null) {
    1049                if (parent.bitIndex == -1) {
    1050                    buffer.append("parent=").append("ROOT");
    1051                } else {
    1052                    buffer.append("parent=").append(parent.getKey()).append(" [").append(parent.bitIndex).append("]");
    1053                }
    1054            } else {
    1055                buffer.append("parent=").append("null");
    1056            }
    1057            buffer.append(", ");
    1058
    1059            if (left != null) {
    1060                if (left.bitIndex == -1) {
    1061                    buffer.append("left=").append("ROOT");
    1062                } else {
    1063                    buffer.append("left=").append(left.getKey()).append(" [").append(left.bitIndex).append("]");
    1064                }
    1065            } else {
    1066                buffer.append("left=").append("null");
    1067            }
    1068            buffer.append(", ");
    1069
    1070            if (right != null) {
    1071                if (right.bitIndex == -1) {
    1072                    buffer.append("right=").append("ROOT");
    1073                } else {
    1074                    buffer.append("right=").append(right.getKey()).append(" [").append(right.bitIndex).append("]");
    1075                }
    1076            } else {
    1077                buffer.append("right=").append("null");
    1078            }
    1079            buffer.append(", ");
    1080
    1081            if (predecessor != null) {
    1082                if (predecessor.bitIndex == -1) {
    1083                    buffer.append("predecessor=").append("ROOT");
    1084                } else {
    1085                    buffer.append("predecessor=").append(predecessor.getKey()).append(" [").
    1086                           append(predecessor.bitIndex).append("]");
    1087                }
    1088            }
    1089
    1090            buffer.append(")");
    1091            return buffer.toString();
    1092        }
    1093    }
    1094
    1095    /**
    1096     * An {@link OrderedMapIterator} for a {@link org.apache.commons.collections4.Trie}.
    1097     */
    1098    private final class TrieMapIterator extends AbstractTrieIterator<K> implements OrderedMapIterator<K, V> {
    1099
    1100        protected TrieEntry<K, V> previous; // the previous node to return
    1101
    1102        @Override
    1103        public K getKey() {
    1104            if (current == null) {
    1105                throw new IllegalStateException();
    1106            }
    1107            return current.getKey();
    1108        }
    1109
    1110        @Override
    1111        public V getValue() {
    1112            if (current == null) {
    1113                throw new IllegalStateException();
    1114            }
    1115            return current.getValue();
    1116        }
    1117
    1118        @Override
    1119        public boolean hasPrevious() {
    1120            return previous != null;
    1121        }
    1122
    1123        @Override
    1124        public K next() {
    1125            return nextEntry().getKey();
    1126        }
    1127
    1128        @Override
    1129        protected TrieEntry<K, V> nextEntry() {
    1130            final TrieEntry<K, V> nextEntry = super.nextEntry();
    1131            previous = nextEntry;
    1132            return nextEntry;
    1133        }
    1134
    1135        @Override
    1136        public K previous() {
    1137            return previousEntry().getKey();
    1138        }
    1139
    1140        protected TrieEntry<K, V> previousEntry() {
    1141            if (expectedModCount != AbstractPatriciaTrie.this.modCount) {
    1142                throw new ConcurrentModificationException();
    1143            }
    1144
    1145            final TrieEntry<K, V> e = previous;
    1146            if (e == null) {
    1147                throw new NoSuchElementException();
    1148            }
    1149
    1150            previous = AbstractPatriciaTrie.this.previousEntry(e);
    1151            next = current;
    1152            current = e;
    1153            return current;
    1154        }
    1155
    1156        @Override
    1157        public V setValue(final V value) {
    1158            if (current == null) {
    1159                throw new IllegalStateException();
    1160            }
    1161            return current.setValue(value);
    1162        }
    1163
    1164    }
    1165
    1166    /**
    1167     * This is a value view of the {@link org.apache.commons.collections4.Trie} as returned by {@link Map#values()}.
    1168     */
    1169    private final class Values extends AbstractCollection<V> {
    1170
    1171        /**
    1172         * An {@link Iterator} that returns Value Objects.
    1173         */
    1174        private final class ValueIterator extends AbstractTrieIterator<V> {
    1175            @Override
    1176            public V next() {
    1177                return nextEntry().getValue();
    1178            }
    1179        }
    1180
    1181        @Override
    1182        public void clear() {
    1183            AbstractPatriciaTrie.this.clear();
    1184        }
    1185
    1186        @Override
    1187        public boolean contains(final Object o) {
    1188            return containsValue(o);
    1189        }
    1190
    1191        @Override
    1192        public Iterator<V> iterator() {
    1193            return new ValueIterator();
    1194        }
    1195
    1196        @Override
    1197        public boolean remove(final Object o) {
    1198            for (final Iterator<V> it = iterator(); it.hasNext(); ) {
    1199                final V value = it.next();
    1200                if (compare(value, o)) {
    1201                    it.remove();
    1202                    return true;
    1203                }
    1204            }
    1205            return false;
    1206        }
    1207
    1208        @Override
    1209        public int size() {
    1210            return AbstractPatriciaTrie.this.size();
    1211        }
    1212    }
    1213
    1214    private static final long serialVersionUID = 5155253417231339498L;
    1215
    1216    /**
    1217     * Returns true if 'next' is a valid uplink coming from 'from'.
    1218     */
    1219    static boolean isValidUplink(final TrieEntry<?, ?> next, final TrieEntry<?, ?> from) {
    1220        return next != null && next.bitIndex <= from.bitIndex && !next.isEmpty();
    1221    }
    1222
    1223    /** The root node of the {@link org.apache.commons.collections4.Trie}. */
    1224    private transient TrieEntry<K, V> root = new TrieEntry<>(null, null, -1);
    1225
    1226    /**
    1227     * Each of these fields are initialized to contain an instance of the
    1228     * appropriate view the first time this view is requested. The views are
    1229     * stateless, so there's no reason to create more than one of each.
    1230     */
    1231    private transient volatile Set<K> keySet;
    1232
    1233    private transient volatile Collection<V> values;
    1234
    1235    private transient volatile Set<Map.Entry<K, V>> entrySet;
    1236
    1237    /** The current size of the {@link org.apache.commons.collections4.Trie}. */
    1238    private transient int size;
    1239
    1240    /**
    1241     * The number of times this {@link org.apache.commons.collections4.Trie} has been modified.
    1242     * It's used to detect concurrent modifications and fail-fast the {@link Iterator}s.
    1243     */
    1244    protected transient int modCount;
    1245
    1246    /**
    1247     * Constructs a new {@link Trie} using the given {@link KeyAnalyzer}.
    1248     *
    1249     * @param keyAnalyzer  the {@link KeyAnalyzer} to use
    1250     */
    1251    protected AbstractPatriciaTrie(final KeyAnalyzer<? super K> keyAnalyzer) {
    1252        super(keyAnalyzer);
    1253    }
    1254
    1255    /**
    1256     * Constructs a new {@link org.apache.commons.collections4.Trie}
    1257     * using the given {@link KeyAnalyzer} and initializes the {@link org.apache.commons.collections4.Trie}
    1258     * with the values from the provided {@link Map}.
    1259     */
    1260    protected AbstractPatriciaTrie(final KeyAnalyzer<? super K> keyAnalyzer,
    1261                                   final Map<? extends K, ? extends V> map) {
    1262        super(keyAnalyzer);
    1263        putAll(map);
    1264    }
    1265
    1266    /**
    1267     * Adds the given {@link TrieEntry} to the {@link org.apache.commons.collections4.Trie}.
    1268     */
    1269    TrieEntry<K, V> addEntry(final TrieEntry<K, V> entry, final int lengthInBits) {
    1270        TrieEntry<K, V> current = root.left;
    1271        TrieEntry<K, V> path = root;
    1272        while (true) {
    1273            if (current.bitIndex >= entry.bitIndex
    1274                    || current.bitIndex <= path.bitIndex) {
    1275                entry.predecessor = entry;
    1276
    1277                if (!isBitSet(entry.key, entry.bitIndex, lengthInBits)) {
    1278                    entry.left = entry;
    1279                    entry.right = current;
    1280                } else {
    1281                    entry.left = current;
    1282                    entry.right = entry;
    1283                }
    1284
    1285                entry.parent = path;
    1286                if (current.bitIndex >= entry.bitIndex) {
    1287                    current.parent = entry;
    1288                }
    1289
    1290                // if we inserted an uplink, set the predecessor on it
    1291                if (current.bitIndex <= path.bitIndex) {
    1292                    current.predecessor = entry;
    1293                }
    1294
    1295                if (path == root || !isBitSet(entry.key, path.bitIndex, lengthInBits)) {
    1296                    path.left = entry;
    1297                } else {
    1298                    path.right = entry;
    1299                }
    1300
    1301                return entry;
    1302            }
    1303
    1304            path = current;
    1305
    1306            if (!isBitSet(entry.key, current.bitIndex, lengthInBits)) {
    1307                current = current.left;
    1308            } else {
    1309                current = current.right;
    1310            }
    1311        }
    1312    }
    1313
    1314    /**
    1315     * Returns a key-value mapping associated with the least key greater
    1316     * than or equal to the given key, or null if there is no such key.
    1317     */
    1318    TrieEntry<K, V> ceilingEntry(final K key) {
    1319        // Basically:
    1320        // Follow the steps of adding an entry, but instead...
    1321        //
    1322        // - If we ever encounter a situation where we found an equal
    1323        //   key, we return it immediately.
    1324        //
    1325        // - If we hit an empty root, return the first iterable item.
    1326        //
    1327        // - If we have to add a new item, we temporarily add it,
    1328        //   find the successor to it, then remove the added item.
    1329        //
    1330        // These steps ensure that the returned value is either the
    1331        // entry for the key itself, or the first entry directly after
    1332        // the key.
    1333
    1334        // TODO: Cleanup so that we don't actually have to add/remove from the
    1335        //       tree.  (We do it here because there are other well-defined
    1336        //       functions to perform the search.)
    1337        final int lengthInBits = lengthInBits(key);
    1338
    1339        if (lengthInBits == 0) {
    1340            if (!root.isEmpty()) {
    1341                return root;
    1342            }
    1343            return firstEntry();
    1344        }
    1345
    1346        final TrieEntry<K, V> found = getNearestEntryForKey(key, lengthInBits);
    1347        if (compareKeys(key, found.key)) {
    1348            return found;
    1349        }
    1350
    1351        final int bitIndex = bitIndex(key, found.key);
    1352        if (KeyAnalyzer.isValidBitIndex(bitIndex)) {
    1353            final TrieEntry<K, V> added = new TrieEntry<>(key, null, bitIndex);
    1354            addEntry(added, lengthInBits);
    1355            incrementSize(); // must increment because remove will decrement
    1356            final TrieEntry<K, V> ceil = nextEntry(added);
    1357            removeEntry(added);
    1358            modCount -= 2; // we didn't really modify it.
    1359            return ceil;
    1360        }
    1361        if (KeyAnalyzer.isNullBitKey(bitIndex)) {
    1362            if (!root.isEmpty()) {
    1363                return root;
    1364            }
    1365            return firstEntry();
    1366        }
    1367        if (KeyAnalyzer.isEqualBitKey(bitIndex)) {
    1368            return found;
    1369        }
    1370
    1371        // we should have exited above.
    1372        throw new IllegalStateException("invalid lookup: " + key);
    1373    }
    1374
    1375    @Override
    1376    public void clear() {
    1377        root.key = null;
    1378        root.bitIndex = -1;
    1379        root.value = null;
    1380
    1381        root.parent = null;
    1382        root.left = root;
    1383        root.right = null;
    1384        root.predecessor = root;
    1385
    1386        size = 0;
    1387        incrementModCount();
    1388    }
    1389
    1390    @Override
    1391    public Comparator<? super K> comparator() {
    1392        return getKeyAnalyzer();
    1393    }
    1394
    1395    @Override
    1396    public boolean containsKey(final Object k) {
    1397        if (k == null) {
    1398            return false;
    1399        }
    1400
    1401        final K key = castKey(k);
    1402        final int lengthInBits = lengthInBits(key);
    1403        final TrieEntry<K, V> entry = getNearestEntryForKey(key, lengthInBits);
    1404        return !entry.isEmpty() && compareKeys(key, entry.key);
    1405    }
    1406
    1407    /**
    1408     * A helper method to decrement the {@link org.apache.commons.collections4.Trie} size and increment the modification counter.
    1409     */
    1410    void decrementSize() {
    1411        size--;
    1412        incrementModCount();
    1413    }
    1414
    1415    @Override
    1416    public Set<Map.Entry<K, V>> entrySet() {
    1417        if (entrySet == null) {
    1418            entrySet = new EntrySet();
    1419        }
    1420        return entrySet;
    1421    }
    1422
    1423    /**
    1424     * Returns the first entry the {@link org.apache.commons.collections4.Trie} is storing.
    1425     * <p>
    1426     * This is implemented by going always to the left until
    1427     * we encounter a valid uplink. That uplink is the first key.
    1428     */
    1429    TrieEntry<K, V> firstEntry() {
    1430        // if Trie is empty, no first node.
    1431        if (isEmpty()) {
    1432            return null;
    1433        }
    1434
    1435        return followLeft(root);
    1436    }
    1437
    1438    @Override
    1439    public K firstKey() {
    1440        if (isEmpty()) {
    1441            throw new NoSuchElementException();
    1442        }
    1443        return firstEntry().getKey();
    1444    }
    1445
    1446    /**
    1447     * Returns a key-value mapping associated with the greatest key
    1448     * less than or equal to the given key, or null if there is no such key.
    1449     */
    1450    TrieEntry<K, V> floorEntry(final K key) {
    1451        // TODO: Cleanup so that we don't actually have to add/remove from the
    1452        //       tree.  (We do it here because there are other well-defined
    1453        //       functions to perform the search.)
    1454        final int lengthInBits = lengthInBits(key);
    1455
    1456        if (lengthInBits == 0) {
    1457            if (!root.isEmpty()) {
    1458                return root;
    1459            }
    1460            return null;
    1461        }
    1462
    1463        final TrieEntry<K, V> found = getNearestEntryForKey(key, lengthInBits);
    1464        if (compareKeys(key, found.key)) {
    1465            return found;
    1466        }
    1467
    1468        final int bitIndex = bitIndex(key, found.key);
    1469        if (KeyAnalyzer.isValidBitIndex(bitIndex)) {
    1470            final TrieEntry<K, V> added = new TrieEntry<>(key, null, bitIndex);
    1471            addEntry(added, lengthInBits);
    1472            incrementSize(); // must increment because remove will decrement
    1473            final TrieEntry<K, V> floor = previousEntry(added);
    1474            removeEntry(added);
    1475            modCount -= 2; // we didn't really modify it.
    1476            return floor;
    1477        }
    1478        if (KeyAnalyzer.isNullBitKey(bitIndex)) {
    1479            if (!root.isEmpty()) {
    1480                return root;
    1481            }
    1482            return null;
    1483        }
    1484        if (KeyAnalyzer.isEqualBitKey(bitIndex)) {
    1485            return found;
    1486        }
    1487
    1488        // we should have exited above.
    1489        throw new IllegalStateException("invalid lookup: " + key);
    1490    }
    1491
    1492    /**
    1493     * Goes left through the tree until it finds a valid node.
    1494     */
    1495    TrieEntry<K, V> followLeft(TrieEntry<K, V> node) {
    1496        while (true) {
    1497            TrieEntry<K, V> child = node.left;
    1498            // if we hit root and it didn't have a node, go right instead.
    1499            if (child.isEmpty()) {
    1500                child = node.right;
    1501            }
    1502
    1503            if (child.bitIndex <= node.bitIndex) {
    1504                return child;
    1505            }
    1506
    1507            node = child;
    1508        }
    1509    }
    1510
    1511    /**
    1512     * Traverses down the right path until it finds an uplink.
    1513     */
    1514    TrieEntry<K, V> followRight(TrieEntry<K, V> node) {
    1515        // if Trie is empty, no last entry.
    1516        if (node.right == null) {
    1517            return null;
    1518        }
    1519
    1520        // Go as far right as possible, until we encounter an uplink.
    1521        while (node.right.bitIndex > node.bitIndex) {
    1522            node = node.right;
    1523        }
    1524
    1525        return node.right;
    1526    }
    1527
    1528    @Override
    1529    public V get(final Object k) {
    1530        final TrieEntry<K, V> entry = getEntry(k);
    1531        return entry != null ? entry.getValue() : null;
    1532    }
    1533
    1534    /**
    1535     * Returns the entry associated with the specified key in the
    1536     * PatriciaTrieBase.  Returns null if the map contains no mapping
    1537     * for this key.
    1538     * <p>
    1539     * This may throw ClassCastException if the object is not of type K.
    1540     */
    1541    TrieEntry<K, V> getEntry(final Object k) {
    1542        final K key = castKey(k);
    1543        if (key == null) {
    1544            return null;
    1545        }
    1546
    1547        final int lengthInBits = lengthInBits(key);
    1548        final TrieEntry<K, V> entry = getNearestEntryForKey(key, lengthInBits);
    1549        return !entry.isEmpty() && compareKeys(key, entry.key) ? entry : null;
    1550    }
    1551
    1552    /**
    1553     * Returns the nearest entry for a given key.  This is useful
    1554     * for finding knowing if a given key exists (and finding the value
    1555     * for it), or for inserting the key.
    1556     *
    1557     * The actual get implementation. This is very similar to
    1558     * selectR but with the exception that it might return the
    1559     * root Entry even if it's empty.
    1560     */
    1561    TrieEntry<K, V> getNearestEntryForKey(final K key, final int lengthInBits) {
    1562        TrieEntry<K, V> current = root.left;
    1563        TrieEntry<K, V> path = root;
    1564        while (true) {
    1565            if (current.bitIndex <= path.bitIndex) {
    1566                return current;
    1567            }
    1568
    1569            path = current;
    1570            if (!isBitSet(key, current.bitIndex, lengthInBits)) {
    1571                current = current.left;
    1572            } else {
    1573                current = current.right;
    1574            }
    1575        }
    1576    }
    1577
    1578    /**
    1579     * Returns a view of this {@link org.apache.commons.collections4.Trie} of all elements that are prefixed
    1580     * by the number of bits in the given Key.
    1581     * <p>
    1582     * The view that this returns is optimized to have a very efficient
    1583     * {@link Iterator}. The {@link SortedMap#firstKey()},
    1584     * {@link SortedMap#lastKey()} &amp; {@link Map#size()} methods must
    1585     * iterate over all possible values in order to determine the results.
    1586     * This information is cached until the PATRICIA {@link org.apache.commons.collections4.Trie} changes.
    1587     * All other methods (except {@link Iterator}) must compare the given
    1588     * key to the prefix to ensure that it is within the range of the view.
    1589     * The {@link Iterator}'s remove method must also relocate the subtree
    1590     * that contains the prefixes if the entry holding the subtree is
    1591     * removed or changes. Changing the subtree takes O(K) time.
    1592     *
    1593     * @param key  the key to use in the search
    1594     * @param offsetInBits  the prefix offset
    1595     * @param lengthInBits  the number of significant prefix bits
    1596     * @return a {@link SortedMap} view of this {@link org.apache.commons.collections4.Trie} with all elements whose
    1597     *   key is prefixed by the search key
    1598     */
    1599    private SortedMap<K, V> getPrefixMapByBits(final K key, final int offsetInBits, final int lengthInBits) {
    1600
    1601        final int offsetLength = offsetInBits + lengthInBits;
    1602        if (offsetLength > lengthInBits(key)) {
    1603            throw new IllegalArgumentException(offsetInBits + " + "
    1604                    + lengthInBits + " > " + lengthInBits(key));
    1605        }
    1606
    1607        if (offsetLength == 0) {
    1608            return this;
    1609        }
    1610
    1611        return new PrefixRangeMap(key, offsetInBits, lengthInBits);
    1612    }
    1613
    1614    @Override
    1615    public SortedMap<K, V> headMap(final K toKey) {
    1616        return new RangeEntryMap(null, toKey);
    1617    }
    1618
    1619    /**
    1620     * Returns an entry strictly higher than the given key,
    1621     * or null if no such entry exists.
    1622     */
    1623    TrieEntry<K, V> higherEntry(final K key) {
    1624        // TODO: Cleanup so that we don't actually have to add/remove from the
    1625        //       tree.  (We do it here because there are other well-defined
    1626        //       functions to perform the search.)
    1627        final int lengthInBits = lengthInBits(key);
    1628
    1629        if (lengthInBits == 0) {
    1630            if (!root.isEmpty()) {
    1631                // If data in root, and more after -- return it.
    1632                if (size() > 1) {
    1633                    return nextEntry(root);
    1634                }
    1635                // If no more after, no higher entry.
    1636                return null;
    1637            }
    1638            // Root is empty & we want something after empty, return first.
    1639            return firstEntry();
    1640        }
    1641
    1642        final TrieEntry<K, V> found = getNearestEntryForKey(key, lengthInBits);
    1643        if (compareKeys(key, found.key)) {
    1644            return nextEntry(found);
    1645        }
    1646
    1647        final int bitIndex = bitIndex(key, found.key);
    1648        if (KeyAnalyzer.isValidBitIndex(bitIndex)) {
    1649            final TrieEntry<K, V> added = new TrieEntry<>(key, null, bitIndex);
    1650            addEntry(added, lengthInBits);
    1651            incrementSize(); // must increment because remove will decrement
    1652            final TrieEntry<K, V> ceil = nextEntry(added);
    1653            removeEntry(added);
    1654            modCount -= 2; // we didn't really modify it.
    1655            return ceil;
    1656        }
    1657        if (KeyAnalyzer.isNullBitKey(bitIndex)) {
    1658            if (!root.isEmpty()) {
    1659                return firstEntry();
    1660            }
    1661            if (size() > 1) {
    1662                return nextEntry(firstEntry());
    1663            }
    1664            return null;
    1665        }
    1666        if (KeyAnalyzer.isEqualBitKey(bitIndex)) {
    1667            return nextEntry(found);
    1668        }
    1669
    1670        // we should have exited above.
    1671        throw new IllegalStateException("invalid lookup: " + key);
    1672    }
    1673
    1674    /**
    1675     * A helper method to increment the modification counter.
    1676     */
    1677    private void incrementModCount() {
    1678        ++modCount;
    1679    }
    1680
    1681    /**
    1682     * A helper method to increment the {@link org.apache.commons.collections4.Trie} size and the modification counter.
    1683     */
    1684    void incrementSize() {
    1685        size++;
    1686        incrementModCount();
    1687    }
    1688
    1689    @Override
    1690    public Set<K> keySet() {
    1691        if (keySet == null) {
    1692            keySet = new KeySet();
    1693        }
    1694        return keySet;
    1695    }
    1696
    1697    /**
    1698     * Returns the last entry the {@link org.apache.commons.collections4.Trie} is storing.
    1699     *
    1700     * <p>This is implemented by going always to the right until
    1701     * we encounter a valid uplink. That uplink is the last key.
    1702     */
    1703    TrieEntry<K, V> lastEntry() {
    1704        return followRight(root.left);
    1705    }
    1706
    1707    @Override
    1708    public K lastKey() {
    1709        final TrieEntry<K, V> entry = lastEntry();
    1710        if (entry != null) {
    1711            return entry.getKey();
    1712        }
    1713        throw new NoSuchElementException();
    1714    }
    1715
    1716    /**
    1717     * Returns a key-value mapping associated with the greatest key
    1718     * strictly less than the given key, or null if there is no such key.
    1719     */
    1720    TrieEntry<K, V> lowerEntry(final K key) {
    1721        // Basically:
    1722        // Follow the steps of adding an entry, but instead...
    1723        //
    1724        // - If we ever encounter a situation where we found an equal
    1725        //   key, we return it's previousEntry immediately.
    1726        //
    1727        // - If we hit root (empty or not), return null.
    1728        //
    1729        // - If we have to add a new item, we temporarily add it,
    1730        //   find the previousEntry to it, then remove the added item.
    1731        //
    1732        // These steps ensure that the returned value is always just before
    1733        // the key or null (if there was nothing before it).
    1734
    1735        // TODO: Cleanup so that we don't actually have to add/remove from the
    1736        //       tree.  (We do it here because there are other well-defined
    1737        //       functions to perform the search.)
    1738        final int lengthInBits = lengthInBits(key);
    1739
    1740        if (lengthInBits == 0) {
    1741            return null; // there can never be anything before root.
    1742        }
    1743
    1744        final TrieEntry<K, V> found = getNearestEntryForKey(key, lengthInBits);
    1745        if (compareKeys(key, found.key)) {
    1746            return previousEntry(found);
    1747        }
    1748
    1749        final int bitIndex = bitIndex(key, found.key);
    1750        if (KeyAnalyzer.isValidBitIndex(bitIndex)) {
    1751            final TrieEntry<K, V> added = new TrieEntry<>(key, null, bitIndex);
    1752            addEntry(added, lengthInBits);
    1753            incrementSize(); // must increment because remove will decrement
    1754            final TrieEntry<K, V> prior = previousEntry(added);
    1755            removeEntry(added);
    1756            modCount -= 2; // we didn't really modify it.
    1757            return prior;
    1758        }
    1759        if (KeyAnalyzer.isNullBitKey(bitIndex)) {
    1760            return null;
    1761        }
    1762        if (KeyAnalyzer.isEqualBitKey(bitIndex)) {
    1763            return previousEntry(found);
    1764        }
    1765
    1766        // we should have exited above.
    1767        throw new IllegalStateException("invalid lookup: " + key);
    1768    }
    1769
    1770    @Override
    1771    public OrderedMapIterator<K, V> mapIterator() {
    1772        return new TrieMapIterator();
    1773    }
    1774
    1775    /**
    1776     * Returns the entry lexicographically after the given entry.
    1777     * If the given entry is null, returns the first node.
    1778     */
    1779    TrieEntry<K, V> nextEntry(final TrieEntry<K, V> node) {
    1780        if (node == null) {
    1781            return firstEntry();
    1782        }
    1783        return nextEntryImpl(node.predecessor, node, null);
    1784    }
    1785
    1786    /**
    1787     * Scans for the next node, starting at the specified point, and using 'previous'
    1788     * as a hint that the last node we returned was 'previous' (so we know not to return
    1789     * it again).  If 'tree' is non-null, this will limit the search to the given tree.
    1790     *
    1791     * The basic premise is that each iteration can follow the following steps:
    1792     *
    1793     * 1) Scan all the way to the left.
    1794     *   a) If we already started from this node last time, proceed to Step 2.
    1795     *   b) If a valid uplink is found, use it.
    1796     *   c) If the result is an empty node (root not set), break the scan.
    1797     *   d) If we already returned the left node, break the scan.
    1798     *
    1799     * 2) Check the right.
    1800     *   a) If we already returned the right node, proceed to Step 3.
    1801     *   b) If it is a valid uplink, use it.
    1802     *   c) Do Step 1 from the right node.
    1803     *
    1804     * 3) Back up through the parents until we encounter find a parent
    1805     *    that we're not the right child of.
    1806     *
    1807     * 4) If there's no right child of that parent, the iteration is finished.
    1808     *    Otherwise continue to Step 5.
    1809     *
    1810     * 5) Check to see if the right child is a valid uplink.
    1811     *    a) If we already returned that child, proceed to Step 6.
    1812     *       Otherwise, use it.
    1813     *
    1814     * 6) If the right child of the parent is the parent itself, we've
    1815     *    already found &amp; returned the end of the Trie, so exit.
    1816     *
    1817     * 7) Do Step 1 on the parent's right child.
    1818     */
    1819    TrieEntry<K, V> nextEntryImpl(final TrieEntry<K, V> start,
    1820            final TrieEntry<K, V> previous, final TrieEntry<K, V> tree) {
    1821
    1822        TrieEntry<K, V> current = start;
    1823
    1824        // Only look at the left if this was a recursive or
    1825        // the first check, otherwise we know we've already looked
    1826        // at the left.
    1827        if (previous == null || start != previous.predecessor) {
    1828            while (!current.left.isEmpty()) {
    1829                // stop traversing if we've already
    1830                // returned the left of this node.
    1831                if (previous == current.left) {
    1832                    break;
    1833                }
    1834
    1835                if (isValidUplink(current.left, current)) {
    1836                    return current.left;
    1837                }
    1838
    1839                current = current.left;
    1840            }
    1841        }
    1842
    1843        // If there's no data at all, exit.
    1844        if (current.isEmpty()) {
    1845            return null;
    1846        }
    1847
    1848        // If we've already returned the left,
    1849        // and the immediate right is null,
    1850        // there's only one entry in the Trie
    1851        // which is stored at the root.
    1852        //
    1853        //  / ("")   <-- root
    1854        //  \_/  \
    1855        //       null <-- 'current'
    1856        //
    1857        if (current.right == null) {
    1858            return null;
    1859        }
    1860
    1861        // If nothing valid on the left, try the right.
    1862        if (previous != current.right) {
    1863            // See if it immediately is valid.
    1864            if (isValidUplink(current.right, current)) {
    1865                return current.right;
    1866            }
    1867
    1868            // Must search on the right's side if it wasn't initially valid.
    1869            return nextEntryImpl(current.right, previous, tree);
    1870        }
    1871
    1872        // Neither left nor right are valid, find the first parent
    1873        // whose child did not come from the right & traverse it.
    1874        while (current == current.parent.right) {
    1875            // If we're going to traverse to above the subtree, stop.
    1876            if (current == tree) {
    1877                return null;
    1878            }
    1879
    1880            current = current.parent;
    1881        }
    1882
    1883        // If we're on the top of the subtree, we can't go any higher.
    1884        if (current == tree) {
    1885            return null;
    1886        }
    1887
    1888        // If there's no right, the parent must be root, so we're done.
    1889        if (current.parent.right == null) {
    1890            return null;
    1891        }
    1892
    1893        // If the parent's right points to itself, we've found one.
    1894        if (previous != current.parent.right
    1895                && isValidUplink(current.parent.right, current.parent)) {
    1896            return current.parent.right;
    1897        }
    1898
    1899        // If the parent's right is itself, there can't be any more nodes.
    1900        if (current.parent.right == current.parent) {
    1901            return null;
    1902        }
    1903
    1904        // We need to traverse down the parent's right's path.
    1905        return nextEntryImpl(current.parent.right, previous, tree);
    1906    }
    1907
    1908    /**
    1909     * Returns the entry lexicographically after the given entry.
    1910     * If the given entry is null, returns the first node.
    1911     *
    1912     * This will traverse only within the subtree.  If the given node
    1913     * is not within the subtree, this will have undefined results.
    1914     */
    1915    TrieEntry<K, V> nextEntryInSubtree(final TrieEntry<K, V> node,
    1916            final TrieEntry<K, V> parentOfSubtree) {
    1917        if (node == null) {
    1918            return firstEntry();
    1919        }
    1920        return nextEntryImpl(node.predecessor, node, parentOfSubtree);
    1921    }
    1922
    1923    @Override
    1924    public K nextKey(final K key) {
    1925        Objects.requireNonNull(key, "key");
    1926        final TrieEntry<K, V> entry = getEntry(key);
    1927        if (entry != null) {
    1928            final TrieEntry<K, V> nextEntry = nextEntry(entry);
    1929            return nextEntry != null ? nextEntry.getKey() : null;
    1930        }
    1931        return null;
    1932    }
    1933
    1934    @Override
    1935    public SortedMap<K, V> prefixMap(final K key) {
    1936        return getPrefixMapByBits(key, 0, lengthInBits(key));
    1937    }
    1938
    1939    /**
    1940     * Returns the node lexicographically before the given node (or null if none).
    1941     *
    1942     * This follows four simple branches:
    1943     *  - If the uplink that returned us was a right uplink:
    1944     *      - If predecessor's left is a valid uplink from predecessor, return it.
    1945     *      - Else, follow the right path from the predecessor's left.
    1946     *  - If the uplink that returned us was a left uplink:
    1947     *      - Loop back through parents until we encounter a node where
    1948     *        node != node.parent.left.
    1949     *          - If node.parent.left is uplink from node.parent:
    1950     *              - If node.parent.left is not root, return it.
    1951     *              - If it is root &amp; root isEmpty, return null.
    1952     *              - If it is root &amp; root !isEmpty, return root.
    1953     *          - If node.parent.left is not uplink from node.parent:
    1954     *              - Follow right path for first right child from node.parent.left
    1955     *
    1956     * @param start  the start entry
    1957     */
    1958    TrieEntry<K, V> previousEntry(final TrieEntry<K, V> start) {
    1959        if (start.predecessor == null) {
    1960            throw new IllegalArgumentException("must have come from somewhere!");
    1961        }
    1962
    1963        if (start.predecessor.right == start) {
    1964            if (isValidUplink(start.predecessor.left, start.predecessor)) {
    1965                return start.predecessor.left;
    1966            }
    1967            return followRight(start.predecessor.left);
    1968        }
    1969        TrieEntry<K, V> node = start.predecessor;
    1970        while (node.parent != null && node == node.parent.left) {
    1971            node = node.parent;
    1972        }
    1973
    1974        if (node.parent == null) { // can be null if we're looking up root.
    1975            return null;
    1976        }
    1977
    1978        if (isValidUplink(node.parent.left, node.parent)) {
    1979            if (node.parent.left == root) {
    1980                if (root.isEmpty()) {
    1981                    return null;
    1982                }
    1983                return root;
    1984
    1985            }
    1986            return node.parent.left;
    1987        }
    1988        return followRight(node.parent.left);
    1989    }
    1990
    1991    @Override
    1992    public K previousKey(final K key) {
    1993        Objects.requireNonNull(key, "key");
    1994        final TrieEntry<K, V> entry = getEntry(key);
    1995        if (entry != null) {
    1996            final TrieEntry<K, V> prevEntry = previousEntry(entry);
    1997            return prevEntry != null ? prevEntry.getKey() : null;
    1998        }
    1999        return null;
    2000    }
    2001
    2002    @Override
    2003    public V put(final K key, final V value) {
    2004        Objects.requireNonNull(key, "key");
    2005
    2006        final int lengthInBits = lengthInBits(key);
    2007
    2008        // The only place to store a key with a length
    2009        // of zero bits is the root node
    2010        if (lengthInBits == 0) {
    2011            if (root.isEmpty()) {
    2012                incrementSize();
    2013            } else {
    2014                incrementModCount();
    2015            }
    2016            return root.setKeyValue(key, value);
    2017        }
    2018
    2019        final TrieEntry<K, V> found = getNearestEntryForKey(key, lengthInBits);
    2020        if (compareKeys(key, found.key)) {
    2021            if (found.isEmpty()) { // <- must be the root
    2022                incrementSize();
    2023            } else {
    2024                incrementModCount();
    2025            }
    2026            return found.setKeyValue(key, value);
    2027        }
    2028
    2029        final int bitIndex = bitIndex(key, found.key);
    2030        if (!KeyAnalyzer.isOutOfBoundsIndex(bitIndex)) {
    2031            if (KeyAnalyzer.isValidBitIndex(bitIndex)) { // in 99.999...9% the case
    2032                /* NEW KEY+VALUE TUPLE */
    2033                final TrieEntry<K, V> t = new TrieEntry<>(key, value, bitIndex);
    2034                addEntry(t, lengthInBits);
    2035                incrementSize();
    2036                return null;
    2037            }
    2038            if (KeyAnalyzer.isNullBitKey(bitIndex)) {
    2039                // A bits of the Key are zero. The only place to
    2040                // store such a Key is the root Node!
    2041
    2042                /* NULL BIT KEY */
    2043                if (root.isEmpty()) {
    2044                    incrementSize();
    2045                } else {
    2046                    incrementModCount();
    2047                }
    2048                return root.setKeyValue(key, value);
    2049
    2050            }
    2051            if (KeyAnalyzer.isEqualBitKey(bitIndex) && found != root) { // NOPMD
    2052                incrementModCount();
    2053                return found.setKeyValue(key, value);
    2054            }
    2055        }
    2056
    2057        throw new IllegalArgumentException("Failed to put: " + key + " -> " + value + ", " + bitIndex);
    2058    }
    2059
    2060    /**
    2061     * Reads the content of the stream.
    2062     */
    2063    @SuppressWarnings("unchecked") // This will fail at runtime if the stream is incorrect
    2064    private void readObject(final ObjectInputStream stream) throws IOException, ClassNotFoundException {
    2065        stream.defaultReadObject();
    2066        root = new TrieEntry<>(null, null, -1);
    2067        final int size = stream.readInt();
    2068        for (int i = 0; i < size; i++) {
    2069            final K k = (K) stream.readObject();
    2070            final V v = (V) stream.readObject();
    2071            put(k, v);
    2072        }
    2073    }
    2074
    2075    /**
    2076     * {@inheritDoc}
    2077     *
    2078     * @throws ClassCastException if provided key is of an incompatible type
    2079     */
    2080    @Override
    2081    public V remove(final Object k) {
    2082        if (k == null) {
    2083            return null;
    2084        }
    2085
    2086        final K key = castKey(k);
    2087        final int lengthInBits = lengthInBits(key);
    2088        TrieEntry<K, V> current = root.left;
    2089        TrieEntry<K, V> path = root;
    2090        while (true) {
    2091            if (current.bitIndex <= path.bitIndex) {
    2092                if (!current.isEmpty() && compareKeys(key, current.key)) {
    2093                    return removeEntry(current);
    2094                }
    2095                return null;
    2096            }
    2097
    2098            path = current;
    2099
    2100            if (!isBitSet(key, current.bitIndex, lengthInBits)) {
    2101                current = current.left;
    2102            } else {
    2103                current = current.right;
    2104            }
    2105        }
    2106    }
    2107
    2108    /**
    2109     * Removes a single entry from the {@link org.apache.commons.collections4.Trie}.
    2110     *
    2111     * If we found a Key (Entry h) then figure out if it's
    2112     * an internal (hard to remove) or external Entry (easy
    2113     * to remove)
    2114     */
    2115    V removeEntry(final TrieEntry<K, V> h) {
    2116        if (h != root) {
    2117            if (h.isInternalNode()) {
    2118                removeInternalEntry(h);
    2119            } else {
    2120                removeExternalEntry(h);
    2121            }
    2122        }
    2123
    2124        decrementSize();
    2125        return h.setKeyValue(null, null);
    2126    }
    2127
    2128    /**
    2129     * Removes an external entry from the {@link org.apache.commons.collections4.Trie}.
    2130     *
    2131     * If it's an external Entry then just remove it.
    2132     * This is very easy and straight forward.
    2133     */
    2134    private void removeExternalEntry(final TrieEntry<K, V> h) {
    2135        if (h == root) {
    2136            throw new IllegalArgumentException("Cannot delete root Entry!");
    2137        }
    2138        if (!h.isExternalNode()) {
    2139            throw new IllegalArgumentException(h + " is not an external Entry!");
    2140        }
    2141
    2142        final TrieEntry<K, V> parent = h.parent;
    2143        final TrieEntry<K, V> child = h.left == h ? h.right : h.left;
    2144
    2145        if (parent.left == h) {
    2146            parent.left = child;
    2147        } else {
    2148            parent.right = child;
    2149        }
    2150
    2151        // either the parent is changing, or the predecessor is changing.
    2152        if (child.bitIndex > parent.bitIndex) {
    2153            child.parent = parent;
    2154        } else {
    2155            child.predecessor = parent;
    2156        }
    2157
    2158    }
    2159
    2160    /**
    2161     * Removes an internal entry from the {@link org.apache.commons.collections4.Trie}.
    2162     *
    2163     * If it's an internal Entry then "good luck" with understanding
    2164     * this code. The Idea is essentially that Entry p takes Entry h's
    2165     * place in the trie which requires some re-wiring.
    2166     */
    2167    private void removeInternalEntry(final TrieEntry<K, V> h) {
    2168        if (h == root) {
    2169            throw new IllegalArgumentException("Cannot delete root Entry!");
    2170        }
    2171        if (!h.isInternalNode()) {
    2172            throw new IllegalArgumentException(h + " is not an internal Entry!");
    2173        }
    2174
    2175        final TrieEntry<K, V> p = h.predecessor;
    2176
    2177        // Set P's bitIndex
    2178        p.bitIndex = h.bitIndex;
    2179
    2180        // Fix P's parent, predecessor and child Nodes
    2181        {
    2182            final TrieEntry<K, V> parent = p.parent;
    2183            final TrieEntry<K, V> child = p.left == h ? p.right : p.left;
    2184
    2185            // if it was looping to itself previously,
    2186            // it will now be pointed from its parent
    2187            // (if we aren't removing its parent --
    2188            //  in that case, it remains looping to itself).
    2189            // otherwise, it will continue to have the same
    2190            // predecessor.
    2191            if (p.predecessor == p && p.parent != h) {
    2192                p.predecessor = p.parent;
    2193            }
    2194
    2195            if (parent.left == p) {
    2196                parent.left = child;
    2197            } else {
    2198                parent.right = child;
    2199            }
    2200
    2201            if (child.bitIndex > parent.bitIndex) {
    2202                child.parent = parent;
    2203            }
    2204        }
    2205
    2206        // Fix H's parent and child Nodes
    2207        {
    2208            // If H is a parent of its left and right child
    2209            // then change them to P
    2210            if (h.left.parent == h) {
    2211                h.left.parent = p;
    2212            }
    2213
    2214            if (h.right.parent == h) {
    2215                h.right.parent = p;
    2216            }
    2217
    2218            // Change H's parent
    2219            if (h.parent.left == h) {
    2220                h.parent.left = p;
    2221            } else {
    2222                h.parent.right = p;
    2223            }
    2224        }
    2225
    2226        // Copy the remaining fields from H to P
    2227        //p.bitIndex = h.bitIndex;
    2228        p.parent = h.parent;
    2229        p.left = h.left;
    2230        p.right = h.right;
    2231
    2232        // Make sure that if h was pointing to any uplinks,
    2233        // p now points to them.
    2234        if (isValidUplink(p.left, p)) {
    2235            p.left.predecessor = p;
    2236        }
    2237
    2238        if (isValidUplink(p.right, p)) {
    2239            p.right.predecessor = p;
    2240        }
    2241    }
    2242
    2243    /**
    2244     * Returns the {@link java.util.Map.Entry} whose key is closest in a bitwise XOR
    2245     * metric to the given key. This is NOT lexicographic closeness.
    2246     * For example, given the keys:
    2247     *
    2248     * <ol>
    2249     * <li>D = 1000100
    2250     * <li>H = 1001000
    2251     * <li>L = 1001100
    2252     * </ol>
    2253     *
    2254     * If the {@link org.apache.commons.collections4.Trie} contained 'H' and 'L', a lookup of 'D' would
    2255     * return 'L', because the XOR distance between D &amp; L is smaller
    2256     * than the XOR distance between D &amp; H.
    2257     *
    2258     * @param key  the key to use in the search
    2259     * @return the {@link java.util.Map.Entry} whose key is closest in a bitwise XOR metric
    2260     *   to the provided key
    2261     */
    2262    public Map.Entry<K, V> select(final K key) {
    2263        final int lengthInBits = lengthInBits(key);
    2264        final Reference<Map.Entry<K, V>> reference = new Reference<>();
    2265        if (!selectR(root.left, -1, key, lengthInBits, reference)) {
    2266            return reference.get();
    2267        }
    2268        return null;
    2269    }
    2270
    2271    /**
    2272     * Returns the key that is closest in a bitwise XOR metric to the
    2273     * provided key. This is NOT lexicographic closeness!
    2274     *
    2275     * For example, given the keys:
    2276     *
    2277     * <ol>
    2278     * <li>D = 1000100
    2279     * <li>H = 1001000
    2280     * <li>L = 1001100
    2281     * </ol>
    2282     *
    2283     * If the {@link org.apache.commons.collections4.Trie} contained 'H' and 'L', a lookup of 'D' would
    2284     * return 'L', because the XOR distance between D &amp; L is smaller
    2285     * than the XOR distance between D &amp; H.
    2286     *
    2287     * @param key  the key to use in the search
    2288     * @return the key that is closest in a bitwise XOR metric to the provided key
    2289     */
    2290    public K selectKey(final K key) {
    2291        final Map.Entry<K, V> entry = select(key);
    2292        if (entry == null) {
    2293            return null;
    2294        }
    2295        return entry.getKey();
    2296    }
    2297
    2298    private boolean selectR(final TrieEntry<K, V> h, final int bitIndex,
    2299                            final K key, final int lengthInBits,
    2300                            final Reference<Map.Entry<K, V>> reference) {
    2301
    2302        if (h.bitIndex <= bitIndex) {
    2303            // If we hit the root Node and it is empty
    2304            // we have to look for an alternative best
    2305            // matching node.
    2306            if (!h.isEmpty()) {
    2307                reference.set(h);
    2308                return false;
    2309            }
    2310            return true;
    2311        }
    2312
    2313        if (!isBitSet(key, h.bitIndex, lengthInBits)) {
    2314            if (selectR(h.left, h.bitIndex, key, lengthInBits, reference)) {
    2315                return selectR(h.right, h.bitIndex, key, lengthInBits, reference);
    2316            }
    2317        } else {
    2318            if (selectR(h.right, h.bitIndex, key, lengthInBits, reference)) {
    2319                return selectR(h.left, h.bitIndex, key, lengthInBits, reference);
    2320            }
    2321        }
    2322        return false;
    2323    }
    2324
    2325    /**
    2326     * Returns the value whose key is closest in a bitwise XOR metric to
    2327     * the provided key. This is NOT lexicographic closeness!
    2328     *
    2329     * For example, given the keys:
    2330     *
    2331     * <ol>
    2332     * <li>D = 1000100
    2333     * <li>H = 1001000
    2334     * <li>L = 1001100
    2335     * </ol>
    2336     *
    2337     * If the {@link org.apache.commons.collections4.Trie} contained 'H' and 'L', a lookup of 'D' would
    2338     * return 'L', because the XOR distance between D &amp; L is smaller
    2339     * than the XOR distance between D &amp; H.
    2340     *
    2341     * @param key  the key to use in the search
    2342     * @return the value whose key is closest in a bitwise XOR metric
    2343     * to the provided key
    2344     */
    2345    public V selectValue(final K key) {
    2346        final Map.Entry<K, V> entry = select(key);
    2347        if (entry == null) {
    2348            return null;
    2349        }
    2350        return entry.getValue();
    2351    }
    2352
    2353    @Override
    2354    public int size() {
    2355        return size;
    2356    }
    2357
    2358    @Override
    2359    public SortedMap<K, V> subMap(final K fromKey, final K toKey) {
    2360        return new RangeEntryMap(fromKey, toKey);
    2361    }
    2362
    2363    /**
    2364     * Finds the subtree that contains the prefix.
    2365     *
    2366     * This is very similar to getR but with the difference that
    2367     * we stop the lookup if h.bitIndex > lengthInBits.
    2368     */
    2369    TrieEntry<K, V> subtree(final K prefix, final int offsetInBits, final int lengthInBits) {
    2370        TrieEntry<K, V> current = root.left;
    2371        TrieEntry<K, V> path = root;
    2372        while (true) {
    2373            if (current.bitIndex <= path.bitIndex || lengthInBits <= current.bitIndex) {
    2374                break;
    2375            }
    2376
    2377            path = current;
    2378            if (!isBitSet(prefix, offsetInBits + current.bitIndex, offsetInBits + lengthInBits)) {
    2379                current = current.left;
    2380            } else {
    2381                current = current.right;
    2382            }
    2383        }
    2384
    2385        // Make sure the entry is valid for a subtree.
    2386        final TrieEntry<K, V> entry = current.isEmpty() ? path : current;
    2387
    2388        // If entry is root, it can't be empty.
    2389        if (entry.isEmpty()) {
    2390            return null;
    2391        }
    2392
    2393        final int endIndexInBits = offsetInBits + lengthInBits;
    2394
    2395        // if root && length of root is less than length of lookup,
    2396        // there's nothing.
    2397        // (this prevents returning the whole subtree if root has an empty
    2398        //  string and we want to lookup things with "\0")
    2399        if (entry == root && lengthInBits(entry.getKey()) < endIndexInBits) {
    2400            return null;
    2401        }
    2402
    2403        // Found key's length-th bit differs from our key
    2404        // which means it cannot be the prefix...
    2405        if (isBitSet(prefix, endIndexInBits - 1, endIndexInBits)
    2406                != isBitSet(entry.key, lengthInBits - 1, lengthInBits(entry.key))) {
    2407            return null;
    2408        }
    2409
    2410        // ... or there are less than 'length' equal bits
    2411        final int bitIndex = getKeyAnalyzer().bitIndex(prefix, offsetInBits, lengthInBits,
    2412                                                       entry.key, 0, lengthInBits(entry.getKey()));
    2413
    2414        if (bitIndex >= 0 && bitIndex < lengthInBits) {
    2415            return null;
    2416        }
    2417
    2418        return entry;
    2419    }
    2420
    2421    @Override
    2422    public SortedMap<K, V> tailMap(final K fromKey) {
    2423        return new RangeEntryMap(fromKey, null);
    2424    }
    2425
    2426    @Override
    2427    public Collection<V> values() {
    2428        if (values == null) {
    2429            values = new Values();
    2430        }
    2431        return values;
    2432    }
    2433
    2434    /**
    2435     * Writes the content to the stream for serialization.
    2436     */
    2437    private void writeObject(final ObjectOutputStream stream) throws IOException {
    2438        stream.defaultWriteObject();
    2439        stream.writeInt(this.size());
    2440        for (final Entry<K, V> entry : entrySet()) {
    2441            stream.writeObject(entry.getKey());
    2442            stream.writeObject(entry.getValue());
    2443        }
    2444    }
    2445
    2446}