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input/code.cpp: In function 'void topologicalSort(std::vector<std::vector<int> >&, int)':
input/code.cpp:26:20: warning: comparison of integer expressions of different signedness: 'std::stack<int>::size_type' {aka 'long unsigned int'} and 'int' [-Wsign-compare]
   26 |     if(Stack.size()< n) cout<<"IMPOSSIBLE"<<endl;
      |        ~~~~~~~~~~~~^~~

#include<vector>
#include<iostream>
#include<algorithm>
#include<stack>
using namespace std;


void topologicalSortUtil(int v, vector<vector<int> >& adj,
                         vector<bool>& visited,
                         stack<int>& Stack)
{
    visited[v] = true;
    for (int i : adj[v]) {
        if (!visited[i])
            topologicalSortUtil(i, adj, visited, Stack);
    }
    Stack.push(v);
}
void topologicalSort(vector<vector<int>>&adj, int n){
    stack<int> Stack;
    vector<bool> visisted(n, false);
    for(int i = 0; i < n;++i){
        if(not visisted[i])
            topologicalSortUtil(i, adj, visisted, Stack);
    }
    if(Stack.size()< n) cout<<"IMPOSSIBLE"<<endl;
    else{
        while (!Stack.empty()) {
            cout << ++Stack.top() << " ";
            Stack.pop();
        }
    }
}
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);
    }
    topologicalSort(adj, n);
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: ACCEPTED

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: WRONG ANSWER