php實現二分查找

<?php	function midSch($arr,$key,$up,$down){		if($up<=$down){			$mid=intval(($up+$down)/2);			if($key==$arr[$mid])				return $mid;			elseif($key<$arr[$mid])				return midSch($arr,$key,$up,$mid-1);			else				return midSch($arr,$key,$mid+1,$down);		}		return -1;	}		$arr=array(1,2,3,4,5,6,7,8,9,10,11,12);	$rs=midSch($arr,11,0,count($arr)-1);	echo $rs;?>