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