스택 괄호문제

		Stack<Character> stack = new Stack<>();
        for (char c : s.toCharArray()) {
            if (c == '(' || c == '{') {
                stack.push(c);
            } else {
                if (stack.isEmpty()) {
                    return false;
                }
                char top = stack.pop();
                if ((c == ')' && top != '(') || (c == '}' && top != '{')) {
                    return false;
                }
            }
        }
        return stack.isEmpty();