LeetCode Combinations

class Solution {public:    vector<vector<int> > combine(int n, int k) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        ans.clear();                vector<int> cur;        recursion(n, k, cur, 1);                return ans;    }private:    vector<vector<int> > ans;        void recursion(int n, int k, vector<int> cur, int num) {        if (k == 0){            ans.push_back(cur);        }        else if (num <= n) {            cur.push_back(num);            recursion(n, k - 1, cur, num + 1);            cur.pop_back();            recursion(n, k, cur, num + 1);        }    }};