快速排序查找匹配元素最前面是否有对应得元素

$arr = [1,2,3,3,4,5,6];
	function binSearch($arr,$num,$start,$end){
		if($start > $end){
			return -1;
		}

		$mid = floor(($start+$end)/2);
		$midValue = $arr[$mid];
		if($num < $midValue){
			$mid = $mid-1;
			return binSearch($arr,$num,$start,$mid);
		}elseif($num > $midValue){
			$mid = $mid+1;
			return binSearch($arr,$num,$mid,$end);
		}else{
			if($mid == 0 || $num != $arr[$mid-1]){
				return $mid;
			}else{
				return binSearch($arr,$num,$start,$mid-1);
			}
		}
	}
	$start=0;
	$end = count($arr)-1;
	$index = binSearch($arr,3,$start,$end);
	echo $index;