Course Schedule

#include <bits/stdc++.h>
using namespace std;
// clang-format off
template<typename A, typename B> ostream& operator<<(ostream &os, const pair<A, B> &p) { return os << '(' << p.first << ", " << p.second << ')'; }
template<typename T_container, typename T = typename enable_if<!is_same<T_container, string>::value, typename T_container::value_type>::type> ostream& operator<<(ostream &os, const T_container &v) { os << '{'; string sep; for (const T &x : v) os << sep << x, sep = ", "; return os << '}'; }
void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T) { cerr << ' ' << H; dbg_out(T...); }
template <typename T> istream &operator>>(istream &is, vector<T> &v) { T value; is >> value; v.push_back(value); return is; }
#define preamble ios::sync_with_stdio(0); cin.tie(0); dbg("INIT");
#ifdef DO_DBG
#define dbg(...) cerr << "(" << #__VA_ARGS__ << "):", dbg_out(__VA_ARGS__)
#else
#define dbg(...)
#endif
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
template <typename T> using v = vector<T>;
template <typename T> using us = unordered_set<T>;
template <typename K, typename V> using um = unordered_map<K, V>;
template <typename K, typename V> using p = pair<K, V>;
template <typename T> using pq = priority_queue<T>;
template <typename T> using nl = numeric_limits<T>;
constexpr int MOD = 1e9 + 7;
const int INF = 1e9;
const ld EPS = 1e-9;
#define loopi(n) for (int i = 0; i < n; i++)
#define loopj(n) for (int j = 0; j < n; j++)
#define loopk(n) for (int k = 0; k < n; k++)
#define loopz(n) for (int z = 0; z < n; z++)
#define all(v) v.begin(), v.end()
#define rall(v) v.rbegin(), v.rend()
#define sq(x) ((x) * (x))
#define basic ll n; cin >> n; v<ull> a; loopi(n) cin >> a;
// clang-format on
v<v<ll>> adj;
v<char> state;
bool impossible = false;
v<ll> order;

void dfs(ll node) {
  dbg(node);
  state[node] = 1;
  for (auto n : adj[node]) {
    if (state[n] == 1) {
      impossible = true;
      return;
    }
    if (state[n] == 0)
      dfs(n);
  }
  state[node] = 2;
  order.push_back(node);
}

int main() {
  ll n, m;
  cin >> n >> m;
  adj.resize(n);
  state.resize(n);
  loopi(m) {
    int a, b;
    cin >> a >> b;
    adj[b - 1].push_back(a - 1);
  }
  dbg(n, m, adj);
  loopi(n) {
    if (state[i] == 0)
      dfs(i);
    dbg();
  }
  if (impossible)
    cout << "IMPOSSIBLE";
  else
    for (auto n : order)
      cout << n + 1 << " ";

  cout << "\n";
}

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