# Description

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],
]
``````

The original problem is here.

The original code is here.

# My Solution

I solve this problem in C++, as below:

``````/*
*Combinations
*Author: shuaijiang
*Email: zhaoshuaijiang8@gmail.com
*/
#include<iostream>
#include<vector>
#include<stdlib.h>
using namespace std;

class Solution {
public:
vector<vector<int>> result;
vector<vector<int>> combine(int n, int k) {
if(k<=0)
return result;
vector<int> nums;
vector<int> res;
for(int i=1;i<=n;i++)
nums.push_back(i);
getCombine(nums,res,0,k);
return result;
}
void getCombine(vector<int> &nums, vector<int> res, int start, int k){
if(k == 1){
for(int i=start;i<nums.size();i++){
res.push_back(nums[i]);
result.push_back(res);
res.pop_back();
}
}
for(int i=start;i<nums.size();i++){
res.push_back(nums[i]);
getCombine(nums,res,i+1,k-1);
res.pop_back();
}
}
};
``````

# Note

To solve this problem, recursion is needed.