static const Dict brackets = {'{': '}', '[': ']', '(': ')'}; static const Set all_brackets = {'{','}','[',']','(',')'}; bool checkBrackets(String s) { Stack stack; foreach (char c in s) { if (c not in all_brackets) continue; if (c in brackets.keys()) stack.push(s); else if (stack.empty() || brackets[stack.pop()] != c) return false; } return (stack.empty()) }