stack<char> c_stack;
        for(int i = 0;i<s.length();i++){
            if(s[i] == '('){
                c_stack.push(')');
            }
            else if(s[i] == '['){
                c_stack.push(']');
            }
            else if(s[i] == '{'){
                c_stack.push('}');
            }
            else if(c_stack.empty()){
                return false;
            }
            else if(s[i] != c_stack.top()){
                return false;
            }
            else{
                c_stack.pop();
            }
        }
        return c_stack.empty();