Course Schedule

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

vector<int> adj[(int)1e5];
int s[(int)1e5];

int main() {
	stack<int> st;
	vector<int> out;

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

	for (int i=0; i<n; i++) {
		s[i] = 0;
		st.push(n-i-1);
	}
	for (int i=0; i<m; i++) {
		int a,b;
		cin >> a >> b;
		a--; b--;
		adj[a].push_back(b);
	}
	
	int sn = 0;
	while (!st.empty() && sn < n) {
		int a = st.top();
		if (s[a] == 2) {
			st.pop();
		}
		else if (s[a] == 1) {
			s[a] = 2;
			sn += 1;
			st.pop();
			out.push_back(a);
		}
		else s[a] = 1;

		for (auto b : adj[a]) {
			if (s[b] == 1) {
				cout << "IMPOSSIBLE";
				return 0;
			}
			if (s[b] == 0) {
				st.push(b);
			}
		}
	}

	for (int i=n-1; i>=0; i--) {
		cout << out[i]+1 << " ";
	}
	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