Course Schedule

#include <bits/stdc++.h>

using namespace std;
#define int long long
#define vout(x) for(int i=0;i<(long long)x.size();i++) printf("%lld ",x[i]); 

// g++ <filename>.cpp -g -Wall -Wextra -DDEBUG -o <executable>

// copied from: https://codeforces.com/blog/entry/79024
// === Debug macro starts here ===

int recur_depth = 0;
#ifdef DEBUG
#define dbg(x) {++recur_depth; auto x_=x; --recur_depth; cerr<<string(recur_depth, '\t')<<"\e[91m"<<__func__<<":"<<__LINE__<<"\t"<<#x<<" = "<<x_<<"\e[39m"<<endl;}
#else
#define dbg(x)
#endif
template<typename Ostream, typename Cont>
typename enable_if<is_same<Ostream,ostream>::value, Ostream&>::type operator<<(Ostream& os,  const Cont& v){
	os<<"[";
	for(auto& x:v){os<<x<<", ";}
	return os<<"]";
}
template<typename Ostream, typename ...Ts>
Ostream& operator<<(Ostream& os,  const pair<Ts...>& p){
	return os<<"{"<<p.first<<", "<<p.second<<"}";
}

// === Debug macro ends here ===

// Topological Sorting

vector<int> course_list;
bool has_cycle = false;

void dfs(vector<int> &state, vector<vector<int>> &adj, int current_node) {
    
    state[current_node] = 1;

    for (int c : adj[current_node]) {
        if (state[c] == 0) {
            dfs(state, adj, c);
        }
        else if (state[c] == 1) {
            has_cycle = true;
        }
    }

    state[current_node] = 2;
    course_list.push_back(current_node);
}
   

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

    vector<int> state(n+1, 0);
    vector<vector<int>> courses(n + 1);
    
    for (int i = 0; i < m; i++) {
        int a, b;
        cin >> a >> b;
        courses[a].push_back(b);
    }

    for (int i = 1; i <= n; i++) {
        if (state[i] == 0) {
            dfs(state, courses, i);
        }
    }

    reverse(course_list.begin(), course_list.end());

    if (has_cycle) {
        cout << "IMPOSSIBLE";
    } 
    else {
        vout(course_list);
    }
    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