Permutations

#include <algorithm>
#include <iostream>
#include <vector>
using namespace std;
int main() {
  vector<int> v;
  const int n = 4;
  for (int i = 0; i < n; i++) v.push_back(i + 1);
  do {
    for (int e: v) cout << e << ' '; cout << endl;
  } while (next_permutation(v.begin(), v.end()));
}