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<?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) 2005-2009 Zend Technologies USA Inc. (http://www.zend.com)
* @license http://framework.zend.com/license/new-bsd New BSD License
* @version $Id: PriorityQueue.php 16541 2009-07-07 06:59:03Z bkarwin $
*/
/**
* 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) 2005-2009 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);
}
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