LeetCode 77. Combinations

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n.

For example,If n = 4 and k = 2, a solution is:

[  [2,4],  [3,4],  [2,3],  [1,2],  [1,3],  [1,4],]answer:
class Solution {public:    vector<vector<int>> combine(int n, int k) {        vector<vector<int>> result;        vector<int> temp;        myCombine(0,n,k,temp,result);        return result;    }        void myCombine(int index, int n, int k,vector<int>& temp,vector<vector<int>>& result){        if(index > n || k < 0) return;        if(k == 0){            result.push_back(temp);            return;        }         for(int i = index + 1; i <= n; i ++){            temp.push_back(i);            myCombine(i,n,k - 1,temp,result);            temp.pop_back();        }    }};