Untitled

class Solution {
public:
    void solve(int k,int start,vector<int>&comb,vector<vector<int>>&res,int n){
        if(comb.size()==k) {
            res.push_back(comb);
            return;
        }
        for(int i=start;i<=n;i++){
            comb.push_back(i);
            solve(k,i+1,comb,res,n);
            comb.pop_back();
        }
    }

    vector<vector<int>> combine(int n, int k) {
        vector<vector<int>> res;
        vector<int> comb;
        solve(k,1,comb,res,n);
        return res;
    }
};