LeetCode - Combinations

class Solution {
public:
    vector<vector<int>> combine(int n, int k) {
        vector<vector<int>> res;
        vector<int> out;
        helper(res, 0, out, k, n);
        return vector<vector<int>>(res.begin(), res.end());
    }
    void helper(vector<vector<int>>& res, int pos, vector<int>& out, int k, int n){
        if(out.size()==k) res.push_back(out);
        else{
           for(int i=pos;i<n;i++){
                out.push_back(i+1);
                helper(res, i+1, out, k, n);
                out.pop_back();
            } 
        }
        
    }
};