Java tutorial
/******************************************************************************* * Copyright 2011 See AUTHORS file. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. ******************************************************************************/ package com.badlogic.gdx.utils; import com.badlogic.gdx.math.MathUtils; import java.util.Iterator; import java.util.NoSuchElementException; /** An unordered set where the keys are objects. This implementation uses cuckoo hashing using 3 hashes, random walking, and a * small stash for problematic keys. Null keys are not allowed. No allocation is done except when growing the table size. <br> * <br> * This set performs very fast contains and remove (typically O(1), worst case O(log(n))). Add may be a bit slower, depending on * hash collisions. Load factors greater than 0.91 greatly increase the chances the set will have to rehash to the next higher POT * size. * @author Nathan Sweet */ public class ObjectSet<T> implements Iterable<T> { private static final int PRIME1 = 0xbe1f14b1; private static final int PRIME2 = 0xb4b82e39; private static final int PRIME3 = 0xced1c241; public int size; T[] keyTable; int capacity, stashSize; private float loadFactor; private int hashShift, mask, threshold; private int stashCapacity; private int pushIterations; private ObjectSetIterator iterator1, iterator2; /** Creates a new set with an initial capacity of 32 and a load factor of 0.8. This set will hold 25 items before growing the * backing table. */ public ObjectSet() { this(32, 0.8f); } /** Creates a new set with a load factor of 0.8. This set will hold initialCapacity * 0.8 items before growing the backing * table. */ public ObjectSet(int initialCapacity) { this(initialCapacity, 0.8f); } /** Creates a new set with the specified initial capacity and load factor. This set will hold initialCapacity * loadFactor items * before growing the backing table. */ public ObjectSet(int initialCapacity, float loadFactor) { if (initialCapacity < 0) throw new IllegalArgumentException("initialCapacity must be >= 0: " + initialCapacity); if (initialCapacity > 1 << 30) throw new IllegalArgumentException("initialCapacity is too large: " + initialCapacity); capacity = MathUtils.nextPowerOfTwo(initialCapacity); if (loadFactor <= 0) throw new IllegalArgumentException("loadFactor must be > 0: " + loadFactor); this.loadFactor = loadFactor; threshold = (int) (capacity * loadFactor); mask = capacity - 1; hashShift = 31 - Integer.numberOfTrailingZeros(capacity); stashCapacity = Math.max(3, (int) Math.ceil(Math.log(capacity)) * 2); pushIterations = Math.max(Math.min(capacity, 8), (int) Math.sqrt(capacity) / 8); keyTable = (T[]) new Object[capacity + stashCapacity]; } /** Creates a new set identical to the specified set. */ public ObjectSet(ObjectSet set) { this(set.capacity, set.loadFactor); stashSize = set.stashSize; System.arraycopy(set.keyTable, 0, keyTable, 0, set.keyTable.length); size = set.size; } /** Returns true if the key was not already in the set. If this set already contains the key, the call leaves the set unchanged * and returns false. */ public boolean add(T key) { if (key == null) throw new IllegalArgumentException("key cannot be null."); T[] keyTable = this.keyTable; // Check for existing keys. int hashCode = key.hashCode(); int index1 = hashCode & mask; T key1 = keyTable[index1]; if (key.equals(key1)) return false; int index2 = hash2(hashCode); T key2 = keyTable[index2]; if (key.equals(key2)) return false; int index3 = hash3(hashCode); T key3 = keyTable[index3]; if (key.equals(key3)) return false; // Find key in the stash. for (int i = capacity, n = i + stashSize; i < n; i++) if (key.equals(keyTable[i])) return false; // Check for empty buckets. if (key1 == null) { keyTable[index1] = key; if (size++ >= threshold) resize(capacity << 1); return true; } if (key2 == null) { keyTable[index2] = key; if (size++ >= threshold) resize(capacity << 1); return true; } if (key3 == null) { keyTable[index3] = key; if (size++ >= threshold) resize(capacity << 1); return true; } push(key, index1, key1, index2, key2, index3, key3); return true; } public void addAll(Array<? extends T> array) { addAll(array, 0, array.size); } public void addAll(Array<? extends T> array, int offset, int length) { if (offset + length > array.size) throw new IllegalArgumentException( "offset + length must be <= size: " + offset + " + " + length + " <= " + array.size); addAll((T[]) array.items, offset, length); } public void addAll(T... array) { addAll(array, 0, array.length); } public void addAll(T[] array, int offset, int length) { ensureCapacity(length); for (int i = offset, n = i + length; i < n; i++) add(array[i]); } public void addAll(ObjectSet<T> set) { ensureCapacity(set.size); for (T key : set) add(key); } /** Skips checks for existing keys. */ private void addResize(T key) { // Check for empty buckets. int hashCode = key.hashCode(); int index1 = hashCode & mask; T key1 = keyTable[index1]; if (key1 == null) { keyTable[index1] = key; if (size++ >= threshold) resize(capacity << 1); return; } int index2 = hash2(hashCode); T key2 = keyTable[index2]; if (key2 == null) { keyTable[index2] = key; if (size++ >= threshold) resize(capacity << 1); return; } int index3 = hash3(hashCode); T key3 = keyTable[index3]; if (key3 == null) { keyTable[index3] = key; if (size++ >= threshold) resize(capacity << 1); return; } push(key, index1, key1, index2, key2, index3, key3); } private void push(T insertKey, int index1, T key1, int index2, T key2, int index3, T key3) { T[] keyTable = this.keyTable; int mask = this.mask; // Push keys until an empty bucket is found. T evictedKey; int i = 0, pushIterations = this.pushIterations; do { // Replace the key and value for one of the hashes. switch (MathUtils.random(2)) { case 0: evictedKey = key1; keyTable[index1] = insertKey; break; case 1: evictedKey = key2; keyTable[index2] = insertKey; break; default: evictedKey = key3; keyTable[index3] = insertKey; break; } // If the evicted key hashes to an empty bucket, put it there and stop. int hashCode = evictedKey.hashCode(); index1 = hashCode & mask; key1 = keyTable[index1]; if (key1 == null) { keyTable[index1] = evictedKey; if (size++ >= threshold) resize(capacity << 1); return; } index2 = hash2(hashCode); key2 = keyTable[index2]; if (key2 == null) { keyTable[index2] = evictedKey; if (size++ >= threshold) resize(capacity << 1); return; } index3 = hash3(hashCode); key3 = keyTable[index3]; if (key3 == null) { keyTable[index3] = evictedKey; if (size++ >= threshold) resize(capacity << 1); return; } if (++i == pushIterations) break; insertKey = evictedKey; } while (true); addStash(evictedKey); } private void addStash(T key) { if (stashSize == stashCapacity) { // Too many pushes occurred and the stash is full, increase the table size. resize(capacity << 1); add(key); return; } // Store key in the stash. int index = capacity + stashSize; keyTable[index] = key; stashSize++; size++; } /** Returns true if the key was removed. */ public boolean remove(T key) { int hashCode = key.hashCode(); int index = hashCode & mask; if (key.equals(keyTable[index])) { keyTable[index] = null; size--; return true; } index = hash2(hashCode); if (key.equals(keyTable[index])) { keyTable[index] = null; size--; return true; } index = hash3(hashCode); if (key.equals(keyTable[index])) { keyTable[index] = null; size--; return true; } return removeStash(key); } boolean removeStash(T key) { T[] keyTable = this.keyTable; for (int i = capacity, n = i + stashSize; i < n; i++) { if (key.equals(keyTable[i])) { removeStashIndex(i); size--; return true; } } return false; } void removeStashIndex(int index) { // If the removed location was not last, move the last tuple to the removed location. stashSize--; int lastIndex = capacity + stashSize; if (index < lastIndex) keyTable[index] = keyTable[lastIndex]; } /** Reduces the size of the backing arrays to be the specified capacity or less. If the capacity is already less, nothing is * done. If the map contains more items than the specified capacity, the next highest power of two capacity is used instead. */ public void shrink(int maximumCapacity) { if (maximumCapacity < 0) throw new IllegalArgumentException("maximumCapacity must be >= 0: " + maximumCapacity); if (size > maximumCapacity) maximumCapacity = size; if (capacity <= maximumCapacity) return; maximumCapacity = MathUtils.nextPowerOfTwo(maximumCapacity); resize(maximumCapacity); } /** Clears the map and reduces the size of the backing arrays to be the specified capacity if they are larger. */ public void clear(int maximumCapacity) { if (capacity <= maximumCapacity) { clear(); return; } size = 0; resize(maximumCapacity); } public void clear() { if (size == 0) return; T[] keyTable = this.keyTable; for (int i = capacity + stashSize; i-- > 0;) keyTable[i] = null; size = 0; stashSize = 0; } public boolean contains(T key) { int hashCode = key.hashCode(); int index = hashCode & mask; if (!key.equals(keyTable[index])) { index = hash2(hashCode); if (!key.equals(keyTable[index])) { index = hash3(hashCode); if (!key.equals(keyTable[index])) return containsKeyStash(key); } } return true; } private boolean containsKeyStash(T key) { T[] keyTable = this.keyTable; for (int i = capacity, n = i + stashSize; i < n; i++) if (key.equals(keyTable[i])) return true; return false; } public T first() { T[] keyTable = this.keyTable; for (int i = 0, n = capacity + stashSize; i < n; i++) if (keyTable[i] != null) return keyTable[i]; throw new IllegalStateException("IntSet is empty."); } /** Increases the size of the backing array to accommodate the specified number of additional items. Useful before adding many * items to avoid multiple backing array resizes. */ public void ensureCapacity(int additionalCapacity) { int sizeNeeded = size + additionalCapacity; if (sizeNeeded >= threshold) resize(MathUtils.nextPowerOfTwo((int) (sizeNeeded / loadFactor))); } private void resize(int newSize) { int oldEndIndex = capacity + stashSize; capacity = newSize; threshold = (int) (newSize * loadFactor); mask = newSize - 1; hashShift = 31 - Integer.numberOfTrailingZeros(newSize); stashCapacity = Math.max(3, (int) Math.ceil(Math.log(newSize)) * 2); pushIterations = Math.max(Math.min(newSize, 8), (int) Math.sqrt(newSize) / 8); T[] oldKeyTable = keyTable; keyTable = (T[]) new Object[newSize + stashCapacity]; int oldSize = size; size = 0; stashSize = 0; if (oldSize > 0) { for (int i = 0; i < oldEndIndex; i++) { T key = oldKeyTable[i]; if (key != null) addResize(key); } } } private int hash2(int h) { h *= PRIME2; return (h ^ h >>> hashShift) & mask; } private int hash3(int h) { h *= PRIME3; return (h ^ h >>> hashShift) & mask; } public String toString() { return '{' + toString(", ") + '}'; } public String toString(String separator) { if (size == 0) return ""; StringBuilder buffer = new StringBuilder(32); T[] keyTable = this.keyTable; int i = keyTable.length; while (i-- > 0) { T key = keyTable[i]; if (key == null) continue; buffer.append(key); break; } while (i-- > 0) { T key = keyTable[i]; if (key == null) continue; buffer.append(separator); buffer.append(key); } return buffer.toString(); } /** Returns an iterator for the keys in the set. Remove is supported. Note that the same iterator instance is returned each time * this method is called. Use the {@link ObjectSetIterator} constructor for nested or multithreaded iteration. */ public ObjectSetIterator<T> iterator() { if (iterator1 == null) { iterator1 = new ObjectSetIterator(this); iterator2 = new ObjectSetIterator(this); } if (!iterator1.valid) { iterator1.reset(); iterator1.valid = true; iterator2.valid = false; return iterator1; } iterator2.reset(); iterator2.valid = true; iterator1.valid = false; return iterator2; } static public <T> ObjectSet<T> with(T... array) { ObjectSet set = new ObjectSet(); set.addAll(array); return set; } static public class ObjectSetIterator<K> implements Iterable<K>, Iterator<K> { public boolean hasNext; final ObjectSet<K> set; int nextIndex, currentIndex; boolean valid = true; public ObjectSetIterator(ObjectSet<K> set) { this.set = set; reset(); } public void reset() { currentIndex = -1; nextIndex = -1; findNextIndex(); } void findNextIndex() { hasNext = false; K[] keyTable = set.keyTable; for (int n = set.capacity + set.stashSize; ++nextIndex < n;) { if (keyTable[nextIndex] != null) { hasNext = true; break; } } } public void remove() { if (currentIndex < 0) throw new IllegalStateException("next must be called before remove."); if (currentIndex >= set.capacity) { set.removeStashIndex(currentIndex); nextIndex = currentIndex - 1; findNextIndex(); } else { set.keyTable[currentIndex] = null; } currentIndex = -1; set.size--; } public boolean hasNext() { if (!valid) throw new GdxRuntimeException("#iterator() cannot be used nested."); return hasNext; } public K next() { if (!hasNext) throw new NoSuchElementException(); if (!valid) throw new GdxRuntimeException("#iterator() cannot be used nested."); K key = set.keyTable[nextIndex]; currentIndex = nextIndex; findNextIndex(); return key; } public Iterator<K> iterator() { return this; } /** Adds the remaining values to the array. */ public Array<K> toArray(Array<K> array) { while (hasNext) array.add(next()); return array; } /** Returns a new array containing the remaining values. */ public Array<K> toArray() { return toArray(new Array(true, set.size)); } } }