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| 1 | +/* |
| 2 | + * Licensed to the Apache Software Foundation (ASF) under one or more |
| 3 | + * contributor license agreements. See the NOTICE file distributed with |
| 4 | + * this work for additional information regarding copyright ownership. |
| 5 | + * The ASF licenses this file to You under the Apache License, Version 2.0 |
| 6 | + * (the "License"); you may not use this file except in compliance with |
| 7 | + * the License. You may obtain a copy of the License at |
| 8 | + * |
| 9 | + * http://www.apache.org/licenses/LICENSE-2.0 |
| 10 | + * |
| 11 | + * Unless required by applicable law or agreed to in writing, software |
| 12 | + * distributed under the License is distributed on an "AS IS" BASIS, |
| 13 | + * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 14 | + * See the License for the specific language governing permissions and |
| 15 | + * limitations under the License. |
| 16 | + */ |
| 17 | +package org.apache.lucene.util; |
| 18 | + |
| 19 | +import java.util.Arrays; |
| 20 | + |
| 21 | +/** |
| 22 | + * A ternary min heap that stores longs; a primitive priority queue that like all priority queues |
| 23 | + * maintains a partial ordering of its elements such that the least element can always be found in |
| 24 | + * constant time. Put()'s and pop()'s require log_3(size). This heap provides unbounded growth via |
| 25 | + * {@link #push(long)}, and bounded-size insertion based on its nominal maxSize via {@link |
| 26 | + * #insertWithOverflow(long)}. The heap is a min heap, meaning that the top element is the lowest |
| 27 | + * value of the heap. TernaryLongHeap implements 3-ary heap. |
| 28 | + * |
| 29 | + * @lucene.internal |
| 30 | + */ |
| 31 | +public final class TernaryLongHeap { |
| 32 | + |
| 33 | + private final int maxSize; |
| 34 | + |
| 35 | + private long[] heap; |
| 36 | + private int size = 0; |
| 37 | + |
| 38 | + /** |
| 39 | + * Constructs a heap with specified size and initializes all elements with the given value. |
| 40 | + * |
| 41 | + * @param size the number of elements to initialize in the heap. |
| 42 | + * @param initialValue the value to fill the heap with. |
| 43 | + */ |
| 44 | + public TernaryLongHeap(int size, long initialValue) { |
| 45 | + this(size <= 0 ? 1 : size); |
| 46 | + Arrays.fill(heap, 1, size + 1, initialValue); |
| 47 | + this.size = size; |
| 48 | + } |
| 49 | + |
| 50 | + /** |
| 51 | + * Create an empty priority queue of the configured initial size. |
| 52 | + * |
| 53 | + * @param maxSize the maximum size of the heap, or if negative, the initial size of an unbounded |
| 54 | + * heap |
| 55 | + */ |
| 56 | + public TernaryLongHeap(int maxSize) { |
| 57 | + if (maxSize < 1 || maxSize >= ArrayUtil.MAX_ARRAY_LENGTH) { |
| 58 | + // Throw exception to prevent confusing OOME: |
| 59 | + throw new IllegalArgumentException( |
| 60 | + "maxSize must be > 0 and < " + (ArrayUtil.MAX_ARRAY_LENGTH - 1) + "; got: " + maxSize); |
| 61 | + } |
| 62 | + // NOTE: we add +1 because all access to heap is 1-based not 0-based. heap[0] is unused. |
| 63 | + final int heapSize = maxSize + 1; |
| 64 | + this.maxSize = maxSize; |
| 65 | + this.heap = new long[heapSize]; |
| 66 | + } |
| 67 | + |
| 68 | + /** |
| 69 | + * Adds a value in log(size) time. Grows unbounded as needed to accommodate new values. |
| 70 | + * |
| 71 | + * @return the new 'top' element in the queue. |
| 72 | + */ |
| 73 | + public long push(long element) { |
| 74 | + size++; |
| 75 | + if (size == heap.length) { |
| 76 | + heap = ArrayUtil.grow(heap, (size * 3 + 1) / 2); |
| 77 | + } |
| 78 | + heap[size] = element; |
| 79 | + LongHeap.upHeap(heap, size, 3); |
| 80 | + return heap[1]; |
| 81 | + } |
| 82 | + |
| 83 | + /** |
| 84 | + * Adds a value to an TernaryLongHeap in log(size) time. If the number of values would exceed the |
| 85 | + * heap's maxSize, the least value is discarded. |
| 86 | + * |
| 87 | + * @return whether the value was added (unless the heap is full, or the new value is less than the |
| 88 | + * top value) |
| 89 | + */ |
| 90 | + public boolean insertWithOverflow(long value) { |
| 91 | + if (size >= maxSize) { |
| 92 | + if (value < heap[1]) { |
| 93 | + return false; |
| 94 | + } |
| 95 | + updateTop(value); |
| 96 | + return true; |
| 97 | + } |
| 98 | + push(value); |
| 99 | + return true; |
| 100 | + } |
| 101 | + |
| 102 | + /** |
| 103 | + * Returns the least element of the TernaryLongHeap in constant time. It is up to the caller to |
| 104 | + * verify that the heap is not empty; no checking is done, and if no elements have been added, 0 |
| 105 | + * is returned. |
| 106 | + */ |
| 107 | + public long top() { |
| 108 | + return heap[1]; |
| 109 | + } |
| 110 | + |
| 111 | + /** |
| 112 | + * Removes and returns the least element of the PriorityQueue in log(size) time. |
| 113 | + * |
| 114 | + * @throws IllegalStateException if the TernaryLongHeap is empty. |
| 115 | + */ |
| 116 | + public long pop() { |
| 117 | + if (size > 0) { |
| 118 | + long result = heap[1]; // save first value |
| 119 | + heap[1] = heap[size]; // move last to first |
| 120 | + size--; |
| 121 | + LongHeap.downHeap(heap, 1, size, 3); // adjust heap |
| 122 | + return result; |
| 123 | + } else { |
| 124 | + throw new IllegalStateException("The heap is empty"); |
| 125 | + } |
| 126 | + } |
| 127 | + |
| 128 | + /** |
| 129 | + * Replace the top of the pq with {@code newTop}. Should be called when the top value changes. |
| 130 | + * Still log(n) worst case, but it's at least twice as fast to |
| 131 | + * |
| 132 | + * <pre class="prettyprint"> |
| 133 | + * pq.updateTop(value); |
| 134 | + * </pre> |
| 135 | + * |
| 136 | + * instead of |
| 137 | + * |
| 138 | + * <pre class="prettyprint"> |
| 139 | + * pq.pop(); |
| 140 | + * pq.push(value); |
| 141 | + * </pre> |
| 142 | + * |
| 143 | + * Calling this method on an empty TernaryLongHeap has no visible effect. |
| 144 | + * |
| 145 | + * @param value the new element that is less than the current top. |
| 146 | + * @return the new 'top' element after shuffling the heap. |
| 147 | + */ |
| 148 | + public long updateTop(long value) { |
| 149 | + heap[1] = value; |
| 150 | + LongHeap.downHeap(heap, 1, size, 3); |
| 151 | + return heap[1]; |
| 152 | + } |
| 153 | + |
| 154 | + /** Returns the number of elements currently stored in the PriorityQueue. */ |
| 155 | + public int size() { |
| 156 | + return size; |
| 157 | + } |
| 158 | + |
| 159 | + /** Removes all entries from the PriorityQueue. */ |
| 160 | + public void clear() { |
| 161 | + size = 0; |
| 162 | + } |
| 163 | + |
| 164 | + public void pushAll(TernaryLongHeap other) { |
| 165 | + for (int i = 1; i <= other.size; i++) { |
| 166 | + push(other.heap[i]); |
| 167 | + } |
| 168 | + } |
| 169 | + |
| 170 | + /** |
| 171 | + * Return the element at the ith location in the heap array. Use for iterating over elements when |
| 172 | + * the order doesn't matter. Note that the valid arguments range from [1, size]. |
| 173 | + */ |
| 174 | + public long get(int i) { |
| 175 | + return heap[i]; |
| 176 | + } |
| 177 | + |
| 178 | + /** |
| 179 | + * This method returns the internal heap array. |
| 180 | + * |
| 181 | + * @lucene.internal |
| 182 | + */ |
| 183 | + // pkg-private for testing |
| 184 | + long[] getHeapArray() { |
| 185 | + return heap; |
| 186 | + } |
| 187 | +} |
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