public static boolean isValid(String s) {
        if (s == null || s.length() % 2 != 0) {
            return false;
        }
        Stack<Character> stack = new Stack<>();
        for (Character curCh : s.toCharArray()) {
            if (curCh == '(' || curCh == '[' || curCh == '{') {
                stack.push(curCh);
            } else  {
                if (stack.isEmpty()) return false;

                char ch = stack.pop();
                if ((curCh == ')' && ch != '(') || (curCh == '}' && ch != '{') || (curCh == ']' && ch != '[')) {
                    return false;
                }
            }
        }

        return stack.isEmpty();
    }