#include <iostream>
#include <vector>
#include <algorithm>
#include <numeric>
using namespace std;

int main() 
{
	int n = 5;
	vector<int> v(n);
	iota(v.begin(), v.end(), 1);
	
	int k = 2;
	vector<int> mask(v.size());
	fill_n(mask.begin(), k, 1);
	
	do 
	{
		for (int i = 0; i < mask.size(); ++i)
		{
			if (mask[i]) { cout << v[i] << " "; }
		}
		cout << "\n";
	} 
	while(prev_permutation(mask.begin(), mask.end()));
}