PHP N-select-M アルゴリズムは大きな配列を出力できません

function Combination($sort, $num){    $result = $data = array();    if( $num == 1 ) {        return $sort;    }    foreach( $sort as $k=>$v ) {        unset($sort[$k]);        $data   = Combination($sort,$num-1);        foreach($data as $row) {            $result[] = $v.','.$row;        }    }    return $result;}$starttime = explode(' ',microtime());$arr    = array(1,2,3,4,5,6,7,8,9,1,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33);//这个是组合$res        = Combination($arr,6);print_r($res);$endtime = explode(' ',microtime());$thistime = $endtime[0]+$endtime[1]-($starttime[0]+$starttime[1]);$thistime = round($thistime,3);echo "本网页执行耗时：".$thistime." 秒";