function nesting(string $s): int
{
    if (empty($s)) {
        return 1;
    }
    $stack = [];
    foreach (str_split($s) as $v) {
        if ($v === ')') {
            if (empty($stack) || array_pop($stack) !== '(') {
                return 0;
            }
        } elseif ( ! empty($v)) {
            $stack[] = $v;
        }
    }

    return empty($stack) ? 1 : 0;
}