PHP实现字符的全排列

//固定递归的出口，就是只剩一个字符的时候，递归的循环过程，就是从每个子串的第二个字符开始依次与第一个字符交换，然后继续处理子串
    public function run($args)
    {
        @set_time_limit(0);
        @ini_set('memory_limit', '2048M');

        $str = $args[0];
        $res = $this->changeStr($str,0,strlen($str)-1);
        var_export($res);
    }

    public function changeStr($str,$p,$max){
        static $result = array();
        if($p == $max){
            if(!in_array($str,$result)){
                echo $str."\n";
                $result[] = $str;
            }else{
                return;
            }
        }else{
            for($i = $p;$i <= $max;$i++){
                if($str[$i] != $str[$i+1]){
                    $str = $this->swap($str,$p,$i);
                    $this->changeStr($str,$p+1,$max);
                    $str = $this->swap($str,$p,$i);
                }
            }
        }
        return $result;
    }

    public function swap($str,$curp,$index){
        $tmp = $str[$index];
        $str[$index] = $str[$curp];
        $str[$curp] = $tmp;
        return $str;
    }