class Solution {
    public boolean isValid(String s){

        Stack<Character> stack = new Stack<>();
        for(int i = 0 ; i < s.length(); i ++){
            char c = s.charAt(i);
            if(c == '(' || c == '[' || c== '{')
                stack.push(c);
            else {
                if(stack.isEmpty())
                    return false;

                char topChar = stack.pop();
                if(c == ')' && topChar != '(')
                    return false;
                if(c == ']' && topChar != '[')
                    return false;
                if(c == '}' && topChar != '{')
                    return false;

                }
            }
            return stack.isEmpty();
        }

        public static void main(String[] args){

            System.out.println((new Solution()).isValid("()[]{}"));
            System.out.println((new Solution()).isValid("(])]{}"));
        }
    }