PHP 빠른 정렬 코드

/**
 * 快速排序
 */
function quick_sort($arr)
{
    $length = count($arr);
    if ($length <= 1) {
        return $arr;
    }
    $left = $right = [];
    for ($i = 1; $i < $length; $i++) {
        if ($arr[$i] < $arr[0]) {
            $left[] = $arr[$i];
        } else {
            $right[] = $arr[$i];
        }

    }
    //递归调用
    $left = quick_sort($left);
    $right = quick_sort($right);
    return array_merge($left, [$arr[0]], $right);
}
$arr_data = [6, 1, 2, 7, 9, 3, 4, 5, 10, 8];
print_r(quick_sort($arr_data));