22. Generate Parentheses - cocoder39/coco39_LC GitHub Wiki

class Solution {
public:
    vector<string> generateParenthesis(int n) {
        vector<string> res;
        string cur;
        helper(res, cur, n, 0, 0);
        return res;
    }
private:
    void helper(vector<string>& res, string& cur, int n, int left, int right) {
        if (left == n && right == n) {
            res.push_back(cur);
            return;
        } else if (left < right || left > n || right > n) {
            return;
        }
        
        cur.push_back('(');
        helper(res, cur, n, left + 1, right);
        cur.pop_back();
        
        cur.push_back(')');
        helper(res, cur, n, left, right + 1);
        cur.pop_back();
    }
};