Course Schedule

#include <bits/stdc++.h>

using namespace std;

const int N = 1e5 + 5;

int n, m;
vector<int> g[N];
vector<int> ord;
int c[N];

void dfs(int u) {
  c[u] = 1;
  for (int v : g[u]) {
    if (c[v] == 1) {
      cout << "IMPOSSIBLE" << '\n';
      exit(0);
    } else if (c[v] == 0) {
      dfs(v);
    }
  }
  c[u] = 2;
  ord.emplace_back(u);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cin >> n >> m;
  for (int i = 1; i <= m; i++) {
    int a, b;
    cin >> a >> b;
    g[a].emplace_back(b);
  }
  for (int i = 1; i <= n; i++) {
    if (c[i] == 0) {
      dfs(i);
    }
  }
  reverse(ord.begin(), ord.end());
  for (int x : ord) {
    cout << x << ' ';
  }
  cout << '\n';
  return 0;
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED