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/library/Zend/Search/Lucene/PriorityQueue.php

https://bitbucket.org/hieronim1981/tunethemusic
PHP | 171 lines | 56 code | 25 blank | 90 comment | 11 complexity | ae0b2f799808549cd142709153b99d68 MD5 | raw file
  1<?php
  2/**
  3 * Zend Framework
  4 *
  5 * LICENSE
  6 *
  7 * This source file is subject to the new BSD license that is bundled
  8 * with this package in the file LICENSE.txt.
  9 * It is also available through the world-wide-web at this URL:
 10 * http://framework.zend.com/license/new-bsd
 11 * If you did not receive a copy of the license and are unable to
 12 * obtain it through the world-wide-web, please send an email
 13 * to license@zend.com so we can send you a copy immediately.
 14 *
 15 * @category   Zend
 16 * @package    Zend_Search_Lucene
 17 * @copyright  Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)
 18 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 19 * @version    $Id: PriorityQueue.php 24593 2012-01-05 20:35:02Z matthew $
 20 */
 21
 22
 23/**
 24 * Abstract Priority Queue
 25 *
 26 * It implements a priority queue.
 27 * Please go to "Data Structures and Algorithms",
 28 * Aho, Hopcroft, and Ullman, Addison-Wesley, 1983 (corrected 1987 edition),
 29 * for implementation details.
 30 *
 31 * It provides O(log(N)) time of put/pop operations, where N is a size of queue
 32 *
 33 * @category   Zend
 34 * @package    Zend_Search_Lucene
 35 * @copyright  Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)
 36 * @license    http://framework.zend.com/license/new-bsd     New BSD License
 37 */
 38abstract class Zend_Search_Lucene_PriorityQueue
 39{
 40    /**
 41     * Queue heap
 42     *
 43     * Heap contains balanced partial ordered binary tree represented in array
 44     * [0] - top of the tree
 45     * [1] - first child of [0]
 46     * [2] - second child of [0]
 47     * ...
 48     * [2*n + 1] - first child of [n]
 49     * [2*n + 2] - second child of [n]
 50     *
 51     * @var array
 52     */
 53    private $_heap = array();
 54
 55
 56    /**
 57     * Add element to the queue
 58     *
 59     * O(log(N)) time
 60     *
 61     * @param mixed $element
 62     */
 63    public function put($element)
 64    {
 65        $nodeId   = count($this->_heap);
 66        $parentId = ($nodeId-1) >> 1;   // floor( ($nodeId-1)/2 )
 67
 68        while ($nodeId != 0  &&  $this->_less($element, $this->_heap[$parentId])) {
 69            // Move parent node down
 70            $this->_heap[$nodeId] = $this->_heap[$parentId];
 71
 72            // Move pointer to the next level of tree
 73            $nodeId   = $parentId;
 74            $parentId = ($nodeId-1) >> 1;   // floor( ($nodeId-1)/2 )
 75        }
 76
 77        // Put new node into the tree
 78        $this->_heap[$nodeId] = $element;
 79    }
 80
 81
 82    /**
 83     * Return least element of the queue
 84     *
 85     * Constant time
 86     *
 87     * @return mixed
 88     */
 89    public function top()
 90    {
 91        if (count($this->_heap) == 0) {
 92            return null;
 93        }
 94
 95        return $this->_heap[0];
 96    }
 97
 98
 99    /**
100     * Removes and return least element of the queue
101     *
102     * O(log(N)) time
103     *
104     * @return mixed
105     */
106    public function pop()
107    {
108        if (count($this->_heap) == 0) {
109            return null;
110        }
111
112        $top = $this->_heap[0];
113        $lastId = count($this->_heap) - 1;
114
115        /**
116         * Find appropriate position for last node
117         */
118        $nodeId  = 0;     // Start from a top
119        $childId = 1;     // First child
120
121        // Choose smaller child
122        if ($lastId > 2  &&  $this->_less($this->_heap[2], $this->_heap[1])) {
123            $childId = 2;
124        }
125
126        while ($childId < $lastId  &&
127               $this->_less($this->_heap[$childId], $this->_heap[$lastId])
128          ) {
129            // Move child node up
130            $this->_heap[$nodeId] = $this->_heap[$childId];
131
132            $nodeId  = $childId;               // Go down
133            $childId = ($nodeId << 1) + 1;     // First child
134
135            // Choose smaller child
136            if (($childId+1) < $lastId  &&
137                $this->_less($this->_heap[$childId+1], $this->_heap[$childId])
138               ) {
139                $childId++;
140            }
141        }
142
143        // Move last element to the new position
144        $this->_heap[$nodeId] = $this->_heap[$lastId];
145        unset($this->_heap[$lastId]);
146
147        return $top;
148    }
149
150
151    /**
152     * Clear queue
153     */
154    public function clear()
155    {
156        $this->_heap = array();
157    }
158
159
160    /**
161     * Compare elements
162     *
163     * Returns true, if $el1 is less than $el2; else otherwise
164     *
165     * @param mixed $el1
166     * @param mixed $el2
167     * @return boolean
168     */
169    abstract protected function _less($el1, $el2);
170}
171