class Solution {

 public:

     vector<vector<int>> combine(int n, int k) {

         vector<vector<int>> res;

         vector<int> nums, temp;

         for(int i = ; i < n; i++)

             nums.push_back(i + );

         cmb(n, k, , nums, temp, res);

         return res;

     }

     void cmb(int n, int k, int idx, vector<int> nums, vector<int> &temp, vector<vector<int>> &res){

         if(k && temp.size() == k)

             res.push_back(temp);

         else if(idx < n){

             temp.push_back(nums[idx]);

             cmb(n, k, idx + , nums, temp, res);

             temp.pop_back();

             cmb(n, k, idx + , nums, temp, res);

         }

     }

 };