LeetCode-Generate Parentheses

 1 class Solution{
 2 public:
 3        void generate(vector<string> &res,string curr,int m,int n){
 4                if(m==0 && n==0){ //递归终止条件
 5                    res.push_back(curr);
 6                    return;
 7                }
 8                
 9                if(m!=0) generate(res,curr+"(",m-1,n);
10                
11                if(m<n && n!=0) generate(res,curr+")",m,n-1);
12        }
13        
14        vector<string> generateParenthesis(int n){
15                vector<string> res;
16                res.clear();
17                
18                if(n>0){
19                    generate(res,string(),n,n);
20                }
21                
22                return ret;
23        }
24 };