/Search/Lucene/PriorityQueue.php
PHP | 171 lines | 56 code | 25 blank | 90 comment | 11 complexity | ae0b2f799808549cd142709153b99d68 MD5 | raw file
- <?php
- /**
- * Zend Framework
- *
- * LICENSE
- *
- * This source file is subject to the new BSD license that is bundled
- * with this package in the file LICENSE.txt.
- * It is also available through the world-wide-web at this URL:
- * http://framework.zend.com/license/new-bsd
- * If you did not receive a copy of the license and are unable to
- * obtain it through the world-wide-web, please send an email
- * to license@zend.com so we can send you a copy immediately.
- *
- * @category Zend
- * @package Zend_Search_Lucene
- * @copyright Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)
- * @license http://framework.zend.com/license/new-bsd New BSD License
- * @version $Id: PriorityQueue.php 24593 2012-01-05 20:35:02Z matthew $
- */
- /**
- * Abstract Priority Queue
- *
- * It implements a priority queue.
- * Please go to "Data Structures and Algorithms",
- * Aho, Hopcroft, and Ullman, Addison-Wesley, 1983 (corrected 1987 edition),
- * for implementation details.
- *
- * It provides O(log(N)) time of put/pop operations, where N is a size of queue
- *
- * @category Zend
- * @package Zend_Search_Lucene
- * @copyright Copyright (c) 2005-2012 Zend Technologies USA Inc. (http://www.zend.com)
- * @license http://framework.zend.com/license/new-bsd New BSD License
- */
- abstract class Zend_Search_Lucene_PriorityQueue
- {
- /**
- * Queue heap
- *
- * Heap contains balanced partial ordered binary tree represented in array
- * [0] - top of the tree
- * [1] - first child of [0]
- * [2] - second child of [0]
- * ...
- * [2*n + 1] - first child of [n]
- * [2*n + 2] - second child of [n]
- *
- * @var array
- */
- private $_heap = array();
- /**
- * Add element to the queue
- *
- * O(log(N)) time
- *
- * @param mixed $element
- */
- public function put($element)
- {
- $nodeId = count($this->_heap);
- $parentId = ($nodeId-1) >> 1; // floor( ($nodeId-1)/2 )
- while ($nodeId != 0 && $this->_less($element, $this->_heap[$parentId])) {
- // Move parent node down
- $this->_heap[$nodeId] = $this->_heap[$parentId];
- // Move pointer to the next level of tree
- $nodeId = $parentId;
- $parentId = ($nodeId-1) >> 1; // floor( ($nodeId-1)/2 )
- }
- // Put new node into the tree
- $this->_heap[$nodeId] = $element;
- }
- /**
- * Return least element of the queue
- *
- * Constant time
- *
- * @return mixed
- */
- public function top()
- {
- if (count($this->_heap) == 0) {
- return null;
- }
- return $this->_heap[0];
- }
- /**
- * Removes and return least element of the queue
- *
- * O(log(N)) time
- *
- * @return mixed
- */
- public function pop()
- {
- if (count($this->_heap) == 0) {
- return null;
- }
- $top = $this->_heap[0];
- $lastId = count($this->_heap) - 1;
- /**
- * Find appropriate position for last node
- */
- $nodeId = 0; // Start from a top
- $childId = 1; // First child
- // Choose smaller child
- if ($lastId > 2 && $this->_less($this->_heap[2], $this->_heap[1])) {
- $childId = 2;
- }
- while ($childId < $lastId &&
- $this->_less($this->_heap[$childId], $this->_heap[$lastId])
- ) {
- // Move child node up
- $this->_heap[$nodeId] = $this->_heap[$childId];
- $nodeId = $childId; // Go down
- $childId = ($nodeId << 1) + 1; // First child
- // Choose smaller child
- if (($childId+1) < $lastId &&
- $this->_less($this->_heap[$childId+1], $this->_heap[$childId])
- ) {
- $childId++;
- }
- }
- // Move last element to the new position
- $this->_heap[$nodeId] = $this->_heap[$lastId];
- unset($this->_heap[$lastId]);
- return $top;
- }
- /**
- * Clear queue
- */
- public function clear()
- {
- $this->_heap = array();
- }
- /**
- * Compare elements
- *
- * Returns true, if $el1 is less than $el2; else otherwise
- *
- * @param mixed $el1
- * @param mixed $el2
- * @return boolean
- */
- abstract protected function _less($el1, $el2);
- }