leetcode-Combinations-77

 1 class Solution {
 2 public:
 3     void dfs(vector<int> v,int i,vector<vector<int> > &ans,vector<int> vv,int k){
 4         if(vv.size()==k){
 5             ans.push_back(vv);
 6             return;
 7         }
 8         for(int j=i+1;j<v.size();j++){
 9             if(j!=i+1&&v[j]==v[j-1]) continue;
10             vv.push_back(v[j]);
11             dfs(v,j,ans,vv,k);
12             vv.pop_back();
13         }
14     }
15     vector<vector<int> > combine(int n, int k) {
16         vector<int> v(n);
17         for(int i=0;i<n;i++) v[i]=i+1;
18         vector<vector<int> > ans;
19         vector<int> vv;
20         for(int i=0;i<v.size();i++){
21             vv.push_back(v[i]);
22             dfs(v,i,ans,vv,k);
23             vv.pop_back();
24         }
25         return ans;
26     }
27 };