Longest route

#include <iostream>
#include <vector>
#include <set>
#include <limits>
using namespace std;

int n, m;
vector<set<int>> matrice;
vector<pair<int, int>> res;
vector<bool> visited;

int dfs(int node) {
    if (visited[node]) {
        return res[node].first;
    }
    if (node == n) {
        res[node] = {1, -1};
        visited[node] = true;
        return 1;
    }
    int max_length = numeric_limits<int>::min();
    int next_node_choice = -1;
    for (int next_node : matrice[node]) {
        int length = dfs(next_node) + 1;
        if (length > max_length) {
            max_length = length;
            next_node_choice = next_node;
        }
    }
    res[node] = {max_length, next_node_choice};
    visited[node] = true;
    return max_length;
}

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

    cin >> n >> m;
    matrice.assign(n + 1, set<int>());
    res.assign(n + 1, {numeric_limits<int>::min(), -1});
    visited.assign(n + 1, false);

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

    int total_length = dfs(1);
    if (res[n].first == numeric_limits<int>::min()) {
        cout << "IMPOSSIBLE\n";
    } else {
        cout << total_length << "\n";
        int node = 1;
        while (node != n) {
            cout << node << " ";
            node = res[node].second;
        }
        cout << n << "\n";
    }

    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

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED