Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

"((()))", "(()())", "(())()", "()(())", "()()()"

New version: 0ms.

class Solution {
private:
    void helper(vector<string>& result, string temp, int left, int right, int n){
        if(left == n && right == n){
            result.push_back(temp);
            return;
        }
        
        if(left < n) helper(result, temp + "(", left + 1, right, n);
        if(left > right) helper(result, temp + ")", left, right + 1, n);
    }
public:
    vector<string> generateParenthesis(int n) {
        vector<string> result;
        helper(result, "", 0, 0, n);
        return result;
    }
};

Runtime: 4ms

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