Combinations

class Solution {private:    vector<vector<int> >res;    void mcombine(int start,int n,int k,vector<int> cur)    {        if(cur.size()==k)        {            res.push_back(cur);            return;        }        if((n-start+1)<(k-cur.size()))        {            return;        }        mcombine(start+1,n,k,cur);        cur.push_back(start);        mcombine(start+1,n,k,cur);    }public:    vector<vector<int> > combine(int n, int k) {        mcombine(1,n,k,vector<int>());        return res;    }};