递归

public function cate_digui($x,$pid,$arr){

       foreach ($x as $v){
           if($v['id']==$pid){
               $arr= $v['id'].','.$arr;
               $arr= self::cate_digui($x, $v['pid'],$arr);
                if($v['pid']==0){
                    return $arr;
                }
           }
       }

          return $arr;

    }