Leetcode: Generate Parentheses

// Interesting questions
// It is very easy to generate duplicated result with normal dp
// The core idea is that from the start to the end of the string,
// we need to keep the property that cnt("(") is more than or equal to cnt(")")
class Solution {
public:
void Generate(int left, int right, string current, vector<string> &res){
if(left==0&&right==0) res.push_back(current);
if(left>0) Generate(left-1,right,current+"(",res);
if(right>left) Generate(left,right-1,current+")",res);
}
vector<string> generateParenthesis(int n) {
vector<string> res;
Generate(n,n,"",res);
return res;
}
};