Dijkstra's algorithm สำหรับหาเส้นทางสั้นที่สุดระหว่างสองจุด ด้วย php

[mindphp]

Dijkstra's algorithm
Dijkstra's algorithm สำหรับหาเส้นทางสั้นที่สุดระหว่างสองจุด ด้วย php

โค้ด: เลือกทั้งหมด

<?PHP
class Dijkstra {
 
	var $visited = array();
	var $distance = array();
	var $previousNode = array();
	var $startnode =null;
	var $map = array();
	var $infiniteDistance = 0;
	var $bestPath = 0;
	var $matrixWidth = 0;
 
	function Dijkstra(&$ourMap, $infiniteDistance) {
		$this -> infiniteDistance = $infiniteDistance;
		$this -> map = &$ourMap;
		$this -> bestPath = 0;
	}
 
	function findShortestPath($start,$to = null) {
		$this -> startnode = $start;
		foreach (array_keys($this->map) as $i) {
			if ($i == $this -> startnode) {
				$this -> visited[$i] = true;
				$this -> distance[$i] = 0;
			} else {
				$this -> visited[$i] = false;
				$this -> distance[$i] = isset($this -> map[$this -> startnode][$i]) 
					? $this -> map[$this -> startnode][$i] 
					: $this -> infiniteDistance;
			}
			$this -> previousNode[$i] = $this -> startnode;
		}
 
		$maxTries = count($this->map);
		$tries = 0;
		while (in_array(false,$this -> visited,true) && $tries <= $maxTries) {			
			$this -> bestPath = $this->findBestPath($this->distance,array_keys($this -> visited,false,true));
			if($to !== null && $this -> bestPath === $to) {
				break;
			}
			$this -> updateDistanceAndPrevious($this -> bestPath);			
			$this -> visited[$this -> bestPath] = true;
			$tries++;
		}
	}
 
	function findBestPath($ourDistance, $ourNodesLeft) {
		$bestPath = $this -> infiniteDistance;
		$bestNode = 0;
		for ($i = 0,$m=count($ourNodesLeft); $i < $m; $i++) {
			if($ourDistance[$ourNodesLeft[$i]] < $bestPath) {
				$bestPath = $ourDistance[$ourNodesLeft[$i]];
				$bestNode = $ourNodesLeft[$i];
			}
		}
		return $bestNode;
	}
 
	function updateDistanceAndPrevious($obp) {		
		foreach (array_keys($this->map) as $i) {
			if( 	(isset($this->map[$obp][$i])) 
			    &&	(!($this->map[$obp][$i] == $this->infiniteDistance) || ($this->map[$obp][$i] == 0 ))	
				&&	(($this->distance[$obp] + $this->map[$obp][$i]) < $this -> distance[$i])
			) 	
			{
					$this -> distance[$i] = $this -> distance[$obp] + $this -> map[$obp][$i];
					$this -> previousNode[$i] = $obp;
			}
		}
	}
 
	function printMap(&$map) {
		$placeholder = ' %' . strlen($this -> infiniteDistance) .'d';
		$foo = '';
		for($i=0,$im=count($map);$i<$im;$i++) {
			for ($k=0,$m=$im;$k<$m;$k++) {
				$foo.= sprintf($placeholder, isset($map[$i][$k]) ? $map[$i][$k] : $this -> infiniteDistance);
			}
			$foo.= "\n";
		}
		return $foo;
	}
 
	function getResults($to = null) {
		$ourShortestPath = array();
		$foo = '';
		foreach (array_keys($this->map) as $i) {
			if($to !== null && $to !== $i) {
				continue;
			}
			$ourShortestPath[$i] = array();
			$endNode = null;
			$currNode = $i;
			$ourShortestPath[$i][] = $i;
			while ($endNode === null || $endNode != $this -> startnode) {
				$ourShortestPath[$i][] = $this -> previousNode[$currNode];
				$endNode = $this -> previousNode[$currNode];
				$currNode = $this -> previousNode[$currNode];
			}
			$ourShortestPath[$i] = array_reverse($ourShortestPath[$i]);
			if ($to === null || $to === $i) {
			if($this -> distance[$i] >= $this -> infiniteDistance) {
				$foo .= sprintf("no route from %d to %d. \n",$this -> startnode,$i);
			} else {
				$foo .= sprintf('%d => %d = %d [%d]: (%s).'."\n" ,
						$this -> startnode,$i,$this -> distance[$i],
						count($ourShortestPath[$i]),
						implode('-',$ourShortestPath[$i]));
			}
			$foo .= str_repeat('-',20) . "\n";
				if ($to === $i) {
					break;
				}
			}
		}
		return $foo;
	}
} // end class 
?>

ตัวอย่างการใช้

โค้ด: เลือกทั้งหมด

<?php
 
// I is the infinite distance.
define('I',1000);
 
// Size of the matrix
$matrixWidth = 20;
 
// $points is an array in the following format: (router1,router2,distance-between-them)
$points = array(
    array(0,1,4),
    array(0,2,I),
    array(1,2,5),
     array(1,3,5),
    array(2,3,5),
    array(3,4,5),
    array(4,5,5),
    array(4,5,5),
    array(2,10,30),
    array(2,11,40),
    array(5,19,20),
    array(10,11,20),
    array(12,13,20),
);
 
$ourMap = array();
 
 
// Read in the points and push them into the map
 
for ($i=0,$m=count($points); $i<$m; $i++) {
    $x = $points[$i][0];
    $y = $points[$i][1];
    $c = $points[$i][2];
    $ourMap[$x][$y] = $c;
    $ourMap[$y][$x] = $c;
}
 
// ensure that the distance from a node to itself is always zero
// Purists may want to edit this bit out.
 
for ($i=0; $i < $matrixWidth; $i++) {
    for ($k=0; $k < $matrixWidth; $k++) {
        if ($i == $k) $ourMap[$i][$k] = 0;
    }
}
 
 
// initialize the algorithm class
$dijkstra = new Dijkstra($ourMap, I,$matrixWidth);
 
// $dijkstra->findShortestPath(0,13); to find only path from field 0 to field 13...
$dijkstra->findShortestPath(0); 
 
// Display the results
 
echo '<pre>';
echo "the map looks like:\n\n";
echo $dijkstra -> printMap($ourMap);
echo "\n\nthe shortest paths from point 0:\n";
echo $dijkstra -> getResults();
echo '</pre>';
 
?>