static const Dict brackets = {'{': '}', '[': ']', '(': ')'};
bool checkBrackets(String s) {
    Stack stack;
    foreach (char c in s) {
        if (c in brackets.keys()) stack.push(s);
        else if (stack.empty() || brackets[stack.pop()] != c) return false;
    }
    return (stack.empty())
}