php关于走楼梯的算法

class Atairs{
private static $numStep=1;
public function goStep($num){

    if($num>1){
        $step=mt_rand(1,2);
        $laststep=$num-$step;
        echo "第".self::$numStep."次走了".$step."步,还有".$laststep."步<br>";
        static::$numStep++;
        self::goStep($laststep);
    }elseif ($num==1) {
        echo "第".self::$numStep."次走了".$num."步,还有0步<br>";
        self::goStep(0);
    }else{
        echo "走完了";
    }
}
}

$obj=new Atairs();
$obj->goStep(50);