[120] | 1 | /** |
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| 2 | * Licensed to the Apache Software Foundation (ASF) under one or more |
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| 3 | * contributor license agreements. See the NOTICE file distributed with |
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| 4 | * this work for additional information regarding copyright ownership. |
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| 5 | * The ASF licenses this file to You under the Apache License, Version 2.0 |
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| 6 | * (the "License"); you may not use this file except in compliance with |
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| 7 | * the License. You may obtain a copy of the License at |
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| 8 | * |
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| 9 | * http://www.apache.org/licenses/LICENSE-2.0 |
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| 10 | * |
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| 11 | * Unless required by applicable law or agreed to in writing, software |
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| 12 | * distributed under the License is distributed on an "AS IS" BASIS, |
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| 13 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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| 14 | * See the License for the specific language governing permissions and |
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| 15 | * limitations under the License. |
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| 16 | */ |
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| 17 | |
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| 18 | package org.apache.hadoop.util; |
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| 19 | |
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| 20 | |
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| 21 | /** A PriorityQueue maintains a partial ordering of its elements such that the |
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| 22 | least element can always be found in constant time. Put()'s and pop()'s |
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| 23 | require log(size) time. */ |
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| 24 | public abstract class PriorityQueue<T> { |
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| 25 | private T[] heap; |
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| 26 | private int size; |
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| 27 | private int maxSize; |
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| 28 | |
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| 29 | /** Determines the ordering of objects in this priority queue. Subclasses |
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| 30 | must define this one method. */ |
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| 31 | protected abstract boolean lessThan(Object a, Object b); |
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| 32 | |
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| 33 | /** Subclass constructors must call this. */ |
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| 34 | @SuppressWarnings("unchecked") |
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| 35 | protected final void initialize(int maxSize) { |
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| 36 | size = 0; |
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| 37 | int heapSize = maxSize + 1; |
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| 38 | heap = (T[]) new Object[heapSize]; |
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| 39 | this.maxSize = maxSize; |
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| 40 | } |
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| 41 | |
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| 42 | /** |
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| 43 | * Adds an Object to a PriorityQueue in log(size) time. |
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| 44 | * If one tries to add more objects than maxSize from initialize |
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| 45 | * a RuntimeException (ArrayIndexOutOfBound) is thrown. |
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| 46 | */ |
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| 47 | public final void put(T element) { |
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| 48 | size++; |
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| 49 | heap[size] = element; |
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| 50 | upHeap(); |
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| 51 | } |
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| 52 | |
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| 53 | /** |
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| 54 | * Adds element to the PriorityQueue in log(size) time if either |
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| 55 | * the PriorityQueue is not full, or not lessThan(element, top()). |
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| 56 | * @param element |
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| 57 | * @return true if element is added, false otherwise. |
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| 58 | */ |
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| 59 | public boolean insert(T element){ |
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| 60 | if (size < maxSize){ |
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| 61 | put(element); |
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| 62 | return true; |
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| 63 | } |
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| 64 | else if (size > 0 && !lessThan(element, top())){ |
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| 65 | heap[1] = element; |
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| 66 | adjustTop(); |
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| 67 | return true; |
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| 68 | } |
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| 69 | else |
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| 70 | return false; |
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| 71 | } |
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| 72 | |
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| 73 | /** Returns the least element of the PriorityQueue in constant time. */ |
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| 74 | public final T top() { |
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| 75 | if (size > 0) |
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| 76 | return heap[1]; |
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| 77 | else |
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| 78 | return null; |
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| 79 | } |
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| 80 | |
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| 81 | /** Removes and returns the least element of the PriorityQueue in log(size) |
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| 82 | time. */ |
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| 83 | public final T pop() { |
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| 84 | if (size > 0) { |
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| 85 | T result = heap[1]; // save first value |
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| 86 | heap[1] = heap[size]; // move last to first |
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| 87 | heap[size] = null; // permit GC of objects |
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| 88 | size--; |
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| 89 | downHeap(); // adjust heap |
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| 90 | return result; |
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| 91 | } else |
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| 92 | return null; |
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| 93 | } |
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| 94 | |
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| 95 | /** Should be called when the Object at top changes values. Still log(n) |
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| 96 | * worst case, but it's at least twice as fast to <pre> |
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| 97 | * { pq.top().change(); pq.adjustTop(); } |
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| 98 | * </pre> instead of <pre> |
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| 99 | * { o = pq.pop(); o.change(); pq.push(o); } |
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| 100 | * </pre> |
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| 101 | */ |
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| 102 | public final void adjustTop() { |
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| 103 | downHeap(); |
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| 104 | } |
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| 105 | |
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| 106 | |
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| 107 | /** Returns the number of elements currently stored in the PriorityQueue. */ |
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| 108 | public final int size() { |
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| 109 | return size; |
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| 110 | } |
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| 111 | |
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| 112 | /** Removes all entries from the PriorityQueue. */ |
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| 113 | public final void clear() { |
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| 114 | for (int i = 0; i <= size; i++) |
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| 115 | heap[i] = null; |
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| 116 | size = 0; |
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| 117 | } |
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| 118 | |
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| 119 | private final void upHeap() { |
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| 120 | int i = size; |
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| 121 | T node = heap[i]; // save bottom node |
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| 122 | int j = i >>> 1; |
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| 123 | while (j > 0 && lessThan(node, heap[j])) { |
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| 124 | heap[i] = heap[j]; // shift parents down |
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| 125 | i = j; |
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| 126 | j = j >>> 1; |
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| 127 | } |
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| 128 | heap[i] = node; // install saved node |
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| 129 | } |
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| 130 | |
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| 131 | private final void downHeap() { |
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| 132 | int i = 1; |
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| 133 | T node = heap[i]; // save top node |
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| 134 | int j = i << 1; // find smaller child |
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| 135 | int k = j + 1; |
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| 136 | if (k <= size && lessThan(heap[k], heap[j])) { |
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| 137 | j = k; |
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| 138 | } |
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| 139 | while (j <= size && lessThan(heap[j], node)) { |
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| 140 | heap[i] = heap[j]; // shift up child |
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| 141 | i = j; |
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| 142 | j = i << 1; |
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| 143 | k = j + 1; |
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| 144 | if (k <= size && lessThan(heap[k], heap[j])) { |
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| 145 | j = k; |
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| 146 | } |
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| 147 | } |
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| 148 | heap[i] = node; // install saved node |
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| 149 | } |
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| 150 | } |
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