//二分查找（数组里查找某个元素） 

function bin_sch($array, $low, $high, $k)
{
    if ($low <= $high) {
        $mid = intval(($low + $high) / 2);
        if ($array[$mid] == $k) {
            return $mid;
        } elseif ($k < $array[$mid]) {
            return bin_sch($array, $low, $mid - 1, $k);
        } else {
            return bin_sch($array, $mid + 1, $high, $k);
        }
    }
    return -1;
}