Combinations

class Solution {public:    vector<vector<int>> combine(int n, int k)     {        vector<vector<int>> result;        vector<int> cur;        dfs(result,cur,1,k,n);        return result;    }    void dfs(vector<vector<int>> &result,vector<int> &cur,int start,int k,int n)    {        if(k==cur.size())        {            result.push_back(cur);            return;        }        else        {                for(int i=start;i<=n;++i)            {                cur.push_back(i);                dfs(result,cur,i+1,k,n);                cur.pop_back();            }        }    }};