https://www.acmicpc.net/problem/15665
#include <iostream>
#include <set>
#include <vector>
using namespace std;
int m;
set<int> s;
vector<int> ans;
void solution(int cnt) {
if(cnt == m) {
for(int i=0; i<m; i++){
cout << ans[i] << " ";
}
cout << "\n";
return;
}
for(auto& e : s) {
ans[cnt] = e;
solution(cnt+1);
}
}
int main()
{
ios_base::sync_with_stdio(false);
cin.tie(NULL);
cout.tie(NULL);
int n;
cin >> n >> m;
while(n--) {
int x;
cin >> x;
s.insert(x);
}
ans.assign(m, 0);
solution(0);
return 0;
}