class Solution {

public:

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

        vector<vector<int> > ans;

        if(n== || n<k)

            return ans;

        vector<int> ansPiece;

        if(n==k)

        {

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

            {

                ansPiece.push_back(i);

            }

            ans.push_back(ansPiece);

            return ans;

        }

        combination2(ans,k,,ansPiece,n);

        return ans;

    }

    void combination2(vector<vector<int> > &ans,int targetLen,int pivot,vector<int> &ansPiece,int n)

    {

        if(targetLen == ansPiece.size())

        {

            ans.push_back(ansPiece);

            return;

        }

        if(pivot > n)

            return;

        combination2( ans,targetLen,pivot+,ansPiece,n);

        ansPiece.push_back(pivot);

        combination2( ans,targetLen,pivot+,ansPiece,n);

        ansPiece.pop_back();

    }

};