class Solution {
public:
    vector<string> Fres;
    void helper(string res, int num_open,int num_close)
    {
        if(num_close==0 && num_open==0)
        {
            Fres.push_back(res);
            return;
        }
        if(num_open>0)
        {
            res.push_back('(');
            helper(res,num_open-1,num_close);
        }
        if(num_open<num_close)
        {
            res.push_back(')');
            helper(res,num_open,num_close-1);
        }
    }
    vector<string> generateParenthesis(int n) {
        helper("",n,n);
        return Fres;
    }
};