Mercurial > hg > blitz_stable

annotate src/EDU/oswego/cs/dl/util/concurrent/Heap.java @ 27:511648fa4d64 Version 2.1

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Version to 2.1
author Dan Creswell <dan.creswell@gmail.com>
date Mon, 04 Jan 2010 13:00:40 +0000
parents 3dc0c5604566
children
Ignore whitespace changes - Everywhere: Within whitespace: At end of lines:
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1 /*
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2 File: Heap.java
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3
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4 Originally written by Doug Lea and released into the public domain.
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5 This may be used for any purposes whatsoever without acknowledgment.
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6 Thanks for the assistance and support of Sun Microsystems Labs,
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7 and everyone contributing, testing, and using this code.
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8
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9 History:
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10 Date Who What
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11 29Aug1998 dl Refactored from BoundedPriorityQueue
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12 08dec2001 dl Null out slots of removed items
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13 03feb2002 dl Also null out in clear
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14 */
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15
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16 package EDU.oswego.cs.dl.util.concurrent;
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17 import java.util.Comparator;
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18
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19 /**
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20 * A heap-based priority queue, without any concurrency control
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21 * (i.e., no blocking on empty/full states).
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22 * This class provides the data structure mechanics for BoundedPriorityQueue.
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23 * <p>
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24 * The class currently uses a standard array-based heap, as described
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25 * in, for example, Sedgewick's Algorithms text. All methods
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26 * are fully synchronized. In the future,
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27 * it may instead use structures permitting finer-grained locking.
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28 * <p>[<a href="http://gee.cs.oswego.edu/dl/classes/EDU/oswego/cs/dl/util/concurrent/intro.html"> Introduction to this package. </a>]
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29 **/
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30
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31 public class Heap {
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32 protected Object[] nodes_; // the tree nodes, packed into an array
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33 protected int count_ = 0; // number of used slots
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34 protected final Comparator cmp_; // for ordering
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35
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36 /**
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37 * Create a Heap with the given initial capacity and comparator
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38 * @exception IllegalArgumentException if capacity less or equal to zero
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39 **/
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40
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41 public Heap(int capacity, Comparator cmp)
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42 throws IllegalArgumentException {
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43 if (capacity <= 0) throw new IllegalArgumentException();
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44 nodes_ = new Object[capacity];
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45 cmp_ = cmp;
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46 }
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47
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48 /**
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49 * Create a Heap with the given capacity,
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50 * and relying on natural ordering.
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51 **/
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52
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53 public Heap(int capacity) {
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54 this(capacity, null);
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55 }
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56
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57
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58 /** perform element comaprisons using comparator or natural ordering **/
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59 protected int compare(Object a, Object b) {
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60 if (cmp_ == null)
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61 return ((Comparable)a).compareTo(b);
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62 else
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63 return cmp_.compare(a, b);
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64 }
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65
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66
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67 // indexes of heap parents and children
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68 protected final int parent(int k) { return (k - 1) / 2; }
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69 protected final int left(int k) { return 2 * k + 1; }
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70 protected final int right(int k) { return 2 * (k + 1); }
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71
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72 /**
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73 * insert an element, resize if necessary
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74 **/
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75 public synchronized void insert(Object x) {
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76 if (count_ >= nodes_.length) {
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77 int newcap = 3 * nodes_.length / 2 + 1;
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78 Object[] newnodes = new Object[newcap];
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79 System.arraycopy(nodes_, 0, newnodes, 0, nodes_.length);
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80 nodes_ = newnodes;
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81 }
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82
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83 int k = count_;
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84 ++count_;
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85 while (k > 0) {
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86 int par = parent(k);
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87 if (compare(x, nodes_[par]) < 0) {
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88 nodes_[k] = nodes_[par];
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89 k = par;
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90 }
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91 else break;
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92 }
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93 nodes_[k] = x;
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94 }
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95
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96
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97 /**
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98 * Return and remove least element, or null if empty
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99 **/
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100
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101 public synchronized Object extract() {
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102 if (count_ < 1) return null;
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103
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104 int k = 0; // take element at root;
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105 Object least = nodes_[k];
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106 --count_;
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107 Object x = nodes_[count_];
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108 nodes_[count_] = null;
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109 for (;;) {
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110 int l = left(k);
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111 if (l >= count_)
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112 break;
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113 else {
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114 int r = right(k);
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115 int child = (r >= count_ || compare(nodes_[l], nodes_[r]) < 0)? l : r;
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116 if (compare(x, nodes_[child]) > 0) {
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117 nodes_[k] = nodes_[child];
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118 k = child;
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119 }
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120 else break;
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121 }
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122 }
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123 nodes_[k] = x;
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124 return least;
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125 }
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126
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127 /** Return least element without removing it, or null if empty **/
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128 public synchronized Object peek() {
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129 if (count_ > 0)
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130 return nodes_[0];
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131 else
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132 return null;
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133 }
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134
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135 /** Return number of elements **/
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136 public synchronized int size() {
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137 return count_;
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138 }
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139
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140 /** remove all elements **/
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141 public synchronized void clear() {
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142 for (int i = 0; i < count_; ++i)
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143 nodes_[i] = null;
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144 count_ = 0;
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145 }
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146
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147 }