LeetCode22：括号生成

 1 class Solution {
 2 private:
 3     int len=0;
 4     vector<string> ret;
 5 public:
 6     vector<string> generateParenthesis(int n) {
 7         vector<char> cur;
 8         len=n;
 9         backtrace(0,0,cur);
10         return ret;
11     }
12 
13     void backtrace(int left, int right, vector<char> cur){
14         if(left==len && right==len){
15             string push="";
16             for(auto it=cur.begin();it!=cur.end();it++)
17                 push+=*it;
18             //cout<<push<<endl;
19             ret.push_back(push);
20 
21         }
22         if(left<len){
23             cur.push_back(‘(‘);
24             backtrace(left+1,right,cur);
25             cur.pop_back();
26         }
27             
28         if(right<len && right<left){
29             cur.push_back(‘)‘);
30             backtrace(left,right+1,cur);
31             cur.pop_back();
32         }
33         return ;
34     }
35 };