1 | //---------------------------------------------------------------------- |
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2 | // File: pr_queue.h |
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3 | // Programmer: Sunil Arya and David Mount |
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4 | // Description: Include file for priority queue and related |
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5 | // structures. |
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6 | // Last modified: 01/04/05 (Version 1.0) |
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7 | //---------------------------------------------------------------------- |
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8 | // Copyright (c) 1997-2005 University of Maryland and Sunil Arya and |
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9 | // David Mount. All Rights Reserved. |
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10 | // |
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11 | // This software and related documentation is part of the Approximate |
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12 | // Nearest Neighbor Library (ANN). This software is provided under |
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13 | // the provisions of the Lesser GNU Public License (LGPL). See the |
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14 | // file ../ReadMe.txt for further information. |
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15 | // |
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16 | // The University of Maryland (U.M.) and the authors make no |
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17 | // representations about the suitability or fitness of this software for |
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18 | // any purpose. It is provided "as is" without express or implied |
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19 | // warranty. |
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20 | //---------------------------------------------------------------------- |
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21 | // History: |
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22 | // Revision 0.1 03/04/98 |
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23 | // Initial release |
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24 | //---------------------------------------------------------------------- |
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25 | |
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26 | #ifndef PR_QUEUE_H |
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27 | #define PR_QUEUE_H |
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28 | |
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29 | #include <ANN/ANNx.h> // all ANN includes |
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30 | #include <ANN/ANNperf.h> // performance evaluation |
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31 | |
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32 | //---------------------------------------------------------------------- |
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33 | // Basic types. |
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34 | //---------------------------------------------------------------------- |
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35 | typedef void *PQinfo; // info field is generic pointer |
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36 | typedef ANNdist PQkey; // key field is distance |
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37 | |
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38 | //---------------------------------------------------------------------- |
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39 | // Priority queue |
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40 | // A priority queue is a list of items, along with associated |
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41 | // priorities. The basic operations are insert and extract_minimum. |
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42 | // |
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43 | // The priority queue is maintained using a standard binary heap. |
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44 | // (Implementation note: Indexing is performed from [1..max] rather |
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45 | // than the C standard of [0..max-1]. This simplifies parent/child |
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46 | // computations.) User information consists of a void pointer, |
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47 | // and the user is responsible for casting this quantity into whatever |
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48 | // useful form is desired. |
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49 | // |
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50 | // Because the priority queue is so central to the efficiency of |
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51 | // query processing, all the code is inline. |
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52 | //---------------------------------------------------------------------- |
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53 | |
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54 | class ANNpr_queue { |
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55 | |
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56 | struct pq_node { // node in priority queue |
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57 | PQkey key; // key value |
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58 | PQinfo info; // info field |
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59 | }; |
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60 | int n; // number of items in queue |
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61 | int max_size; // maximum queue size |
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62 | pq_node *pq; // the priority queue (array of nodes) |
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63 | |
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64 | public: |
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65 | ANNpr_queue(int max) // constructor (given max size) |
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66 | { |
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67 | n = 0; // initially empty |
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68 | max_size = max; // maximum number of items |
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69 | pq = new pq_node[max+1]; // queue is array [1..max] of nodes |
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70 | } |
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71 | |
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72 | ~ANNpr_queue() // destructor |
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73 | { delete [] pq; } |
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74 | |
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75 | ANNbool empty() // is queue empty? |
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76 | { if (n==0) return ANNtrue; else return ANNfalse; } |
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77 | |
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78 | ANNbool non_empty() // is queue nonempty? |
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79 | { if (n==0) return ANNfalse; else return ANNtrue; } |
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80 | |
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81 | void reset() // make existing queue empty |
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82 | { n = 0; } |
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83 | |
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84 | inline void insert( // insert item (inlined for speed) |
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85 | PQkey kv, // key value |
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86 | PQinfo inf) // item info |
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87 | { |
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88 | if (++n > max_size) annError("Priority queue overflow.", ANNabort); |
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89 | register int r = n; |
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90 | while (r > 1) { // sift up new item |
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91 | register int p = r/2; |
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92 | ANN_FLOP(1) // increment floating ops |
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93 | if (pq[p].key <= kv) // in proper order |
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94 | break; |
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95 | pq[r] = pq[p]; // else swap with parent |
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96 | r = p; |
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97 | } |
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98 | pq[r].key = kv; // insert new item at final location |
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99 | pq[r].info = inf; |
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100 | } |
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101 | |
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102 | inline void extr_min( // extract minimum (inlined for speed) |
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103 | PQkey &kv, // key (returned) |
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104 | PQinfo &inf) // item info (returned) |
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105 | { |
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106 | kv = pq[1].key; // key of min item |
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107 | inf = pq[1].info; // information of min item |
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108 | register PQkey kn = pq[n--].key;// last item in queue |
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109 | register int p = 1; // p points to item out of position |
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110 | register int r = p<<1; // left child of p |
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111 | while (r <= n) { // while r is still within the heap |
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112 | ANN_FLOP(2) // increment floating ops |
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113 | // set r to smaller child of p |
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114 | if (r < n && pq[r].key > pq[r+1].key) r++; |
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115 | if (kn <= pq[r].key) // in proper order |
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116 | break; |
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117 | pq[p] = pq[r]; // else swap with child |
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118 | p = r; // advance pointers |
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119 | r = p<<1; |
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120 | } |
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121 | pq[p] = pq[n+1]; // insert last item in proper place |
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122 | } |
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123 | }; |
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124 | |
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125 | #endif |
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