Longest route

// Find longest route from start to end

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

void dfs(vector<vector<long long>> &v, vector<bool> &visited, long long start, long long end, vector<pair<long long, vector<long long>>> &solutions, vector<long long> &path) {
    visited[start] = true;
    path.push_back(start);

    if (start == end) {
        solutions.push_back({path.size(), path});
    }

    for (auto neighbour : v[start]) {
        if (not visited[neighbour])
            dfs(v, visited, neighbour, end, solutions, path);
    }
    path.pop_back();
    visited[start] = false;
}

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

    vector<vector<long long>> adj(n);
    for (int i = 0; i < m; ++i) {
        long long u, v;
        cin >> u >> v;
        adj[u-1].push_back(v-1);
    }

    // DFSs
    vector<pair<long long, vector<long long>>> solutions;
    vector<long long> path;
    vector<bool> visited(n, false);
    dfs(adj, visited, 0, n - 1, solutions, path);

    // Best solution
    auto it = max_element(solutions.begin(), solutions.end());

    // Print solution
    if (it != solutions.end()) {
        cout << (*it).first << endl;
        for (auto city : (*it).second)
            cout << city + 1 << " ";
        cout << endl;
    }
    else
        cout << "IMPOSSIBLE" << endl;
}

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: RUNTIME ERROR

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: RUNTIME ERROR

Test 16

Verdict: ACCEPTED

Test 17

Verdict: RUNTIME ERROR

Test 18

Verdict: TIME LIMIT EXCEEDED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED