leetcode 22 Generate Parentheses

#include<iostream>
#include<string>
#include<vector>

using namespace std;

class Solution {
public:
    vector<string> generateParenthesis(int n) {
 		int left = n;
		int right = n;       
		vector<string> res ;
		string str = "";
		helper(res,left,right,str);
		return res;
    }
public:
	void helper(vector<string> &res,int left,int right,string str){
		if(left > right){
		return ;
		}
		if(left == 0 && right == 0){
			res.push_back(str);
			return;
		}
		if(left > 0){
			helper(res,left-1,right,str+"(");
		}
		if(right > 0){
			helper(res,left,right-1,str+")");
		}
	}
};
int main(){
	Solution so;
	int n = 3;
	vector<string> res = so.generateParenthesis(n);
	int size = res.size();
	for(int i = 0; i< size ; i++ ){
		cout << "item is: " << res[i] << endl;
	}
}