Leetcode 22. 括号生成

class Solution {
public:
    void generate(string item, int left, int right, vector<string>& res)
    {
        if(left==0 && right==0)
        {
            res.push_back(item);
            return;
        }
        if(left > 0)
        {
            generate(item + ‘(‘, left-1 , right, res);
        }
        if(left < right)
        {
            generate(item + ‘)‘, left , right-1, res);
        }
    }
    
    vector<string> generateParenthesis(int n) {
        vector<string> res;
        generate("", n, n, res);
        return res;
    }
};