Longest route

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

typedef long long ll;

int main() {
    ll n, m;

    cin >> n >> m;

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

    if(adj[1].size() == 0) {
        cout << "IMPOSSIBLE" << endl;
        return 0;
    }

    ll distance[n+1];
    for (ll i = 1; i <= n; i++) distance[i] = -1;
    distance[1] = 0;

    priority_queue<pair<ll,ll>> q;
    bool processed[n+1] = {false};

    ll parents[n+1] = {0};

    ll max_dist = 0;
    ll max = 0;
    q.push({0,1});
    while (!q.empty()) {
        ll a = q.top().second; q.pop();
        if (processed[a]) continue;
        processed[a] = true;
        for (auto u : adj[a]) {
            ll b = u;
            if (distance[a]+1 > distance[b]) {
                distance[b] = distance[a]+1;
                parents[u] = a;
                if(max_dist< distance[b]) {
                    max_dist = distance[b];
                    max = b;
                }
                q.push({distance[b],b});
            }
        }
    }

    cout << max_dist+1 << endl;
    a = max;
    ll outputs[n];
    ll id = 0;
    while(a != 1) {
        outputs[id] = a;
        a = parents[a];
        id++;
    }
    outputs[id] = 1;
    for(ll i = id; i>=0; i--) {
        cout << outputs[i] << " ";
    }
    cout <<  "\n";

    // for(ll i = 1; i<= n; i++) {
    //     cout << distance[i]+1 << " ";
    // }
}

Test 1

Verdict: WRONG ANSWER

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: WRONG ANSWER

Test 7

Verdict: WRONG ANSWER

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: WRONG ANSWER

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: WRONG ANSWER

Test 15

Verdict: WRONG ANSWER

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: ACCEPTED

Test 18

Verdict: WRONG ANSWER

Test 19

Verdict: WRONG ANSWER

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED