二分查找完美版

/**
 * 有序数组为升序
 */
function bsearch($start, $end, $des, &$arr) {
    $mid = round(($start+$end)/2);
    
    if ($arr[$start] > $des or $arr[$end] < $des) {
        return FALSE;
    } else if (($end - $start) == 1) {
        return ($arr[$start] == $des or $arr[$end] == $des);
    }
    
    if ($arr[$mid] > $des) {
        return bsearch($start, $mid, $des, $arr);
    } else if ($arr[$mid] == $des) {
        return TRUE;
    } else if ($arr[$mid] < $des) {
        return bsearch($mid, $end, $des, $arr);
    }
}

$arr = array(1,2,3,4,5,9,10,11,54,87);
$ret = bsearch(0, count($arr)-1, 8, $arr);
var_dump($ret);