二分查找

$nums = [1, 2, 3, 4, 5, 6];
	$num=5;
	$start = 0;
	$end = count($nums)-1;
	echo binary_search($nums,$num,$start,$end);
	function binary_search($nums,$num,$start,$end){
		$mid = floor(($start+$end)/2);
		$midNum = $nums[$mid];
		if($num < $midNum){
			$end = $mid-1;
			return binary_search($nums,$num,$start,$end);
		}elseif($num > $midNum){
			$start = $mid+1;
			return binary_search($nums,$num,$start,$end);
		}elseif($midNum == $num){
		   return $mid;
		}
	}