leetcode77 Combinations

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

For example,
If n = 4 and k = 2, a solution is:

[
  [2,4],
  [3,4],
  [2,3],
  [1,2],
  [1,3],
  [1,4],
]

 1 class Solution {
 2 public:
 3     vector<vector<int>> combine(int n, int k) {
 4         vector<vector<int>> ans;
 5         vector<int> temp;
 6         if(k<=n&&k>0)
 7         {
 8             dep(n,1,k,temp,ans);
 9         }
10         return ans;
11     }
12     void dep(int n,int p,int k,vector<int> &temp,vector<vector<int>> &ans)
13     {
14         if(k==0)
15         {
16             ans.push_back(temp);
17             return;
18         }
19         if(p<=n)
20         {
21             temp.push_back(p);
22             dep(n,p+1,k-1,temp,ans);
23             temp.erase(temp.end()-1);
24             dep(n,p+1,k,temp,ans);
25         }
26         
27     }
28 };

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