查找之折半查找

前提：查询数组是一个有序数组

算法思想：取middle=(low+high)/2索引的元素值，比较arr[middle]与result， 若查找值result<arr[middle],对low~middle-1进行如上查找，若result>arr[middle],对middle+1~high进行如上查找，如此循环递归，一直到查得或low>high;

代码：

<?php
    $arr = array(3,12,44,45,54,232,234,289,322,323,456,554,2323,3432,3435,34454,43546);
    function binarySearch(&$arr, $low, $high, $result)
    {
        if($low>$high)
            return "No such digit!";
        $middle = round(($low+$high)/2);
        if($arr[$middle] == $result)
            return $middle;
        else if($result <$arr[$middle])
            return binarySearch($arr, $low, $middle-1, $result);
        else
            return binarySearch($arr, $middle+1, $high, $result);
    }

    echo binarySearch($arr, 0, count($arr)-1, 44);
?>