【leetcode】Generate Parentheses

 1 class Solution {
 2 public:
 3     void unguarded_generate(vector<string> &result,string curr,int m,int n)
 4     {
 5         if (m==0&&n==0)
 6         {
 7             result.push_back(curr);
 8         }
 9         else
10         {
11             if(m!=0)
12             {
13                 unguarded_generate(result,curr+"(",m-1,n);
14             }
15         
16             if(m<n&&n!=0)
17             {
18                 unguarded_generate(result,curr+")",m,n-1);
19             }
20         }
21     }
22  
23     vector<string> generateParenthesis(int n) 
24     {
25         vector<string> ret;
26         if(n>0)
27         {
28             unguarded_generate(ret,string(),n,n);
29         }
30         return ret;
31     }
32 };