Course Schedule

#include <bits/stdc++.h>

using namespace std;

bool topological_sort_rec(int n, vector<vector<int>> &adj, int *state, vector<int> &out, int x) {

    state[x] = 1;

    for (int p : adj[x]) {
        if (state[p] == 1)
            return false;
        else if (state[p] == 0) {
            bool r = topological_sort_rec(n, adj, state, out, p);
            if (!r) return false;
        }
    }

    state[x] = 2;
    out.push_back(x);   
        
    return true;

}

bool topological_sort(int n, vector<vector<int>> &adj, vector<int> &out) {

    int *state = new int[n];
    for (int i = 0; i < n; i++)
        state[i] = 0;
    
    for (int i = 0; i < n; i++) {
        if (state[i] == 0) {
            // not yet visited
            bool r = topological_sort_rec(n, adj, state, out, i);
            if (!r) return false;
        }
    }

    return true;

}

int main() {

    int n, m;
    cin >> n >> m;

    vector<vector<int>> adj(n);

    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        a--, b--;
        adj[a].push_back(b);
    }

    vector<int> order;
    bool success = topological_sort(n, adj, order);

    if (success) {
        for (auto it = order.rbegin(); it < order.rend(); it++)
            cout << (*it + 1) << " ";
        cout << endl;
    } else {
        cout << "IMPOSSIBLE" << 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