php　实现全排列

< ?php
header('Content-Type: text/html; charset=UTF-8');
class quanpailie
{
	var $startTime = 0;
	var $stopTime = 0;
 
    function get_microtime()
    {
        list($usec, $sec) = explode(' ', microtime());
        return ((float)$usec + (float)$sec);
    }
	function start()
    {
        $this->startTime = $this->get_microtime();
    }
	function stop()
	{
		$this->stopTime = $this->get_microtime();
	}
	function spent()
	{
		return round(($this->stopTime - $this->startTime) * 1000, 3);
	}
	function type($list, $k, $m)
	{
		if($k==$m)
		{
			for($i=0; $i< =$m; $i++)
			{
				echo  $list[$i];
			}
			echo "\n";
		}
		else
		{
			for($i=$k; $i<=$m; $i++)
			{
				$this->swap($list[$k], $list[$i]);
				$this->type($list, $k+1, $m);
				$this->swap($list[$k], $list[$i]);
			}
		}
	}
	public function swap(&$a, &$b)
	{
		$temp=$a;
		$a=$b;
		$b=$temp;
	}
}
$aa=new quanpailie();
$aa->start();
$str = 'abcde';
$aa->type(str_split($str), 0, 2);
$aa->stop();
echo "<br />页面执行时间: ". $aa->spent() . " 毫秒";
?>