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input/code.cpp: In function 'int main()':
input/code.cpp:35:19: warning: comparison of integer expressions of different signedness: 'int' and 'unsigned int' [-Wsign-compare]
   35 |     for(int i=0; i<m; i++){
      |                  ~^~
input/code.cpp:52:19: warning: comparison of integer expressions of different signedness: 'int' and 'unsigned int' [-Wsign-compare]
   52 |     for(int i=1; i<n; i++){
      |                  ~^~

#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef unsigned long long ull;

int p[100001];
map<int, vector<int>> adj;
vector<int> order;

bool process(int a){
    if(p[a] == 2) return true;
    if(p[a] == 1) return false;

    p[a] = 1;
    for(auto b : adj[a]){
        if(p[b] == 0){
            if(!process(b)){
                return false;
            }
        }
        if(p[b] == 1){
            return false;
        }
    }
    p[a] = 2;
    // cout << "push: " << a << endl;
    order.push_back(a);
    return true;
}

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

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

    order.reserve(n);
    for(auto&[a,_] : adj){
        // cout << "start: " << a << endl;
        if(!process(a)){
            cout << "IMPOSSIBLE" << endl;
            return 0;
        }
    }

    order = vector(order.rbegin(), order.rend());
    cout << order[0];
    for(int i=1; i<n; i++){
        cout << " " << order[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: RUNTIME ERROR

Test 7

Verdict: RUNTIME ERROR

Test 8

Verdict: RUNTIME ERROR

Test 9

Verdict: RUNTIME ERROR

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