Course Schedule

input/code.cpp: In function 'void solve()':
input/code.cpp:67:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   67 |             if (i < edges[a].size()) {
      |                 ~~^~~~~~~~~~~~~~~~~

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

// debug
template<class T> ostream& operator<<(ostream&, const vector<T>&);
template<class T> ostream& operator<<(ostream&, const set<T>&);
template<class T> ostream& operator<<(ostream&, const multiset<T>&);
template<class K, class V> ostream& operator<<(ostream&, const map<K, V>&);
template<class T, size_t N> ostream& operator<<(ostream&, const array<T, N>&);
template<class A, class B> ostream& operator<<(ostream& os, const pair<A, B>& p) { return os << "(" << p.first << ", " << p.second << ")"; }
template<class T>
void print_collection(ostream& os, const T& v) {
    os << "{";
    bool first = true;
    for (const auto& x : v) {
        if (!first) os << ", ";
        first = false;
        os << x;
    }
    os << "}";
}
template<class T> ostream& operator<<(ostream& os, const vector<T>& v) { print_collection(os, v); return os; }
template<class T> ostream& operator<<(ostream& os, const set<T>& v) { print_collection(os, v); return os; }
template<class T> ostream& operator<<(ostream& os, const multiset<T>& v) { print_collection(os, v); return os; }
template<class K, class V> ostream& operator<<(ostream& os, const map<K, V>& v) { print_collection(os, v); return os; }
template<class T, size_t N> ostream& operator<<(ostream& os, const array<T, N>& v) { print_collection(os, v); return os; }
#define dbg(x) cerr << #x << " = " << (x) << '\n'

using ll = long long;
constexpr int INF = 1'000'000'000; // 1e9
constexpr ll LINF = 1'000'000'000'000'000'000LL; // 1e18
constexpr int MOD = 1'000'000'007; // 1e9 + 7

inline ll add(ll a, ll b) { return (a + b) % MOD; }
inline ll sub(ll a, ll b) { return ((a - b) % MOD + MOD) % MOD; }
inline ll mul(ll a, ll b) { return (a * b) % MOD; }


void solve() {
    int N, M;
    cin >> N >> M;

    vector<vector<int>> edges(N + 1);
    for (int i = 0; i < M; ++i) {
        int a, b;
        cin >> a >> b;
        edges[a].push_back(b);
    }

    vector<int> state(N + 1);
    vector<int> order;
    bool cycle = false;

    for (int start = 1; start <= N; ++start) {
        if (state[start] != 0)
            continue;

        stack<pair<int, int>> s;

        s.push({start, 0});
        state[start] = 1;

        while (!s.empty()) {
            int a = s.top().first;
            int &i = s.top().second;

            if (i < edges[a].size()) {
                int b = edges[a][i++];

                if (state[b] == 0) {
                    state[b] = 1;
                    s.push({b, 0});
                }
                else if (state[b] == 1) {
                    cycle = true;
                }
            }
            else {
                state[a] = 2;
                order.push_back(a);
                s.pop();
            }
        }
    }

    if (cycle) {
        cout << "IMPOSSIBLE\n";
    } else {
        reverse(order.begin(), order.end());
        for(auto o: order) cout << o << " ";
    }
}

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    solve();

    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