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119 lines
4.3 KiB
C++
119 lines
4.3 KiB
C++
//----------------------------------------------------------------------
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// File: pr_queue_k.h
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// Programmer: Sunil Arya and David Mount
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// Description: Include file for priority queue with k items.
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// Last modified: 01/04/05 (Version 1.0)
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//----------------------------------------------------------------------
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// Copyright (c) 1997-2005 University of Maryland and Sunil Arya and
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// David Mount. All Rights Reserved.
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//
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// This software and related documentation is part of the Approximate
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// Nearest Neighbor Library (ANN). This software is provided under
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// the provisions of the Lesser GNU Public License (LGPL). See the
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// file ../ReadMe.txt for further information.
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//
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// The University of Maryland (U.M.) and the authors make no
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// representations about the suitability or fitness of this software for
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// any purpose. It is provided "as is" without express or implied
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// warranty.
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//----------------------------------------------------------------------
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// History:
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// Revision 0.1 03/04/98
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// Initial release
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//----------------------------------------------------------------------
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#ifndef PR_QUEUE_K_H
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#define PR_QUEUE_K_H
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#include <ANN/ANNx.h> // all ANN includes
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#include <ANN/ANNperf.h> // performance evaluation
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//----------------------------------------------------------------------
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// Basic types
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//----------------------------------------------------------------------
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typedef ANNdist PQKkey; // key field is distance
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typedef int PQKinfo; // info field is int
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//----------------------------------------------------------------------
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// Constants
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// The NULL key value is used to initialize the priority queue, and
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// so it should be larger than any valid distance, so that it will
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// be replaced as legal distance values are inserted. The NULL
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// info value must be a nonvalid array index, we use ANN_NULL_IDX,
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// which is guaranteed to be negative.
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//----------------------------------------------------------------------
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const PQKkey PQ_NULL_KEY = ANN_DIST_INF; // nonexistent key value
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const PQKinfo PQ_NULL_INFO = ANN_NULL_IDX; // nonexistent info value
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//----------------------------------------------------------------------
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// ANNmin_k
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// An ANNmin_k structure is one which maintains the smallest
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// k values (of type PQKkey) and associated information (of type
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// PQKinfo). The special info and key values PQ_NULL_INFO and
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// PQ_NULL_KEY means that thise entry is empty.
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//
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// It is currently implemented using an array with k items.
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// Items are stored in increasing sorted order, and insertions
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// are made through standard insertion sort. (This is quite
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// inefficient, but current applications call for small values
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// of k and relatively few insertions.)
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//
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// Note that the list contains k+1 entries, but the last entry
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// is used as a simple placeholder and is otherwise ignored.
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//----------------------------------------------------------------------
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class ANNmin_k {
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struct mk_node { // node in min_k structure
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PQKkey key; // key value
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PQKinfo info; // info field (user defined)
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};
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int k; // max number of keys to store
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int n; // number of keys currently active
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mk_node *mk; // the list itself
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public:
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ANNmin_k(int max) // constructor (given max size)
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{
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n = 0; // initially no items
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k = max; // maximum number of items
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mk = new mk_node[max+1]; // sorted array of keys
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}
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~ANNmin_k() // destructor
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{ delete [] mk; }
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PQKkey ANNmin_key() // return minimum key
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{ return (n > 0 ? mk[0].key : PQ_NULL_KEY); }
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PQKkey max_key() // return maximum key
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{ return (n == k ? mk[k-1].key : PQ_NULL_KEY); }
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PQKkey ith_smallest_key(int i) // ith smallest key (i in [0..n-1])
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{ return (i < n ? mk[i].key : PQ_NULL_KEY); }
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PQKinfo ith_smallest_info(int i) // info for ith smallest (i in [0..n-1])
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{ return (i < n ? mk[i].info : PQ_NULL_INFO); }
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inline void insert( // insert item (inlined for speed)
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PQKkey kv, // key value
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PQKinfo inf) // item info
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{
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register int i;
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// slide larger values up
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for (i = n; i > 0; i--) {
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if (mk[i-1].key > kv)
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mk[i] = mk[i-1];
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else
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break;
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}
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mk[i].key = kv; // store element here
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mk[i].info = inf;
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if (n < k) n++; // increment number of items
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ANN_FLOP(k-i+1) // increment floating ops
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}
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};
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#endif
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