Longest route

#include <bits/stdc++.h>

using namespace std;

#define debug(x) cerr << #x << ": " << x << endl;
#define ll long long
#define ull unsigned long long
#define vi vector<int>




void dfs(int node, vector<vi>& adj, vi& nbcities, vi& parents, int nb) {
    nbcities[node] = nb + 1;
    // Process the current node

    for (int neighbor : adj[node]) {
        if (nbcities[neighbor] < nbcities[node] + 1) {
            parents[neighbor] = node;
            dfs(neighbor, adj, nbcities, parents, nb + 1);
        }
    }
}

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

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

    vi parents (n, -1);
    vi nbcities (n, 0);
    dfs(0, adj, nbcities, parents, 0);

    if (parents[n-1] == -1) {
        cout << "IMPOSSIBLE" << endl;
        return 0;
    }

    list<int> sol;
    for (int v = n-1; v >= 0; v = parents[v])
    {
        sol.push_front(v);
    }

    cout << sol.size() << endl;
    for (auto &&s : sol)
    {
        cout << s + 1 << ' ';
    }
    cout << endl;
    
    

    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: TIME LIMIT EXCEEDED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: TIME LIMIT EXCEEDED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED