Course Schedule

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;

const ll N = 1000000;

vector<ll> adj[N];

ll state[N] = {0};

bool dfs(ll s, vector<ll>& sorted) {
    if (state[s] == 1) return false;
    if (state[s] == 2) return true;
    state[s] = 1;
    for (auto u: adj[s]) {
        if(!dfs(u, sorted)) return false;
    }
    state[s] = 2;
    sorted.push_back(s);
    //cout << "We push state = " << s << endl;
    return true;
}

int main() {
    ll n, m;
    cin >> n >> m;

    ll a,b;
    for(ll i = 0; i<m; i++) {
        cin >> a >> b;
        adj[a].push_back(b);
    }
    vector<ll> sorted;
    for(ll s = 1; s <= n; s++) {
        if(state[s] != 2) {
            if(!dfs(s, sorted)) {
                cout << "IMPOSSIBLE" << endl;
                return 0;
            }
        }
    }
    for(ll i=sorted.size()-1; i>=0; i--) {
        cout << sorted[i] << " ";
    }
    cout << endl;
}

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