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],
]

#include<vector>
using std::vector;
class Solution 
{
public:
	vector<vector<int> > combine(int n, int k) 
	{
		vector<vector<int>> res;
		vector<int> temp(k,0);
		get_res(0,0,k,n,res,temp);
		return res;
	}
	void get_res(int data,int now, int k, int n, vector<vector<int>>& res, vector<int>& temp)
	{
		if(k == now)
		{
			res.push_back(temp);
			return;
		}
		for(int i = data+1; i <= n-k+now+1; i++)
		{
			temp[now] = i;
			get_res(i,now+1,k,n,res,temp);
		}
		return;
	}
};

LeetCode--Combinations