[37] | 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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