php二分式查找

要求数组是有序数组 
1 <?php
 2     #二分查找
 3     function binarySearch(Array $arr, $target) {
 4         $low = 0;
 5         $high = count($arr) - 1;
 6
 7         while($low <= $high) {
 8             $mid = floor(($low + $high) / 2);
 9             #找到元素
10             if($arr[$mid] == $target) return $mid;
11             #中元素比目标大,查找左部
12             if($arr[$mid] > $target) $high = $mid - 1;
13             #重元素比目标小,查找右部
14             if($arr[$mid] < $target) $low = $mid + 1;
15         }
16
17         #查找失败
18         return false;
19     }
20
21     $arr = array(1, 3, 5, 7, 9, 11);
22     $inx = binarySearch($arr, 1);
23     var_dump($inx);
24 ?>