Snakeless path

#include <bits/stdc++.h>

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

    int n, m;
    std::cin >> n >> m;

    std::set<std::pair<int, int>> forbidden;while (m--) {
        int a, b;
        std::cin >> a >> b;
        forbidden.emplace(std::min(a, b), std::max(a, b));
    }

    std::set<int> unvisited;
    for (int i = 1; i <= n; i++) {
        unvisited.emplace(i);
    }
    std::vector parent(n + 1, -1);

    bool found = false;
    std::function<void(int)> dfs = [&](const int node) {
        unvisited.erase(node);

        if (node == n) {
            found = true;
            return;
        }

        for (auto next_node : std::set(unvisited)) {
            const std::pair edge = {std::min(node, next_node), std::max(node, next_node)};
            if (!forbidden.contains(edge)) {
                parent[next_node] = node;
                dfs(next_node);
                if (found) return;
            }
        }
    };

    dfs(1);

    if (!found) {
        std::cout << 0 << std::endl;
        return 0;
    }

    std::vector<int> path;
    for (int v = n; v != -1; v = parent[v]) {
        path.emplace_back(v);
    }

    std::cout << path.size() << '\n';
    std::ranges::reverse(path);
    for (const auto& v : path) {
        std::cout << v << ' ';
    }
    std::cout << std::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: 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

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED

Test 31

Verdict: ACCEPTED

Test 32

Verdict: ACCEPTED

Test 33

Verdict: ACCEPTED

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED

Test 36

Verdict: ACCEPTED

Test 37

Verdict: ACCEPTED

Test 38

Verdict: ACCEPTED

Test 39

Verdict: ACCEPTED

Test 40

Verdict: ACCEPTED

Test 41

Verdict: ACCEPTED

Test 42

Verdict: ACCEPTED

Test 43

Verdict: ACCEPTED

Test 44

Verdict: ACCEPTED

Test 45

Verdict: ACCEPTED

Test 46

Verdict: ACCEPTED

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: ACCEPTED

Test 51

Verdict: ACCEPTED

Test 52

Verdict: ACCEPTED

Test 53

Verdict: ACCEPTED

Test 54

Verdict: ACCEPTED

Test 55

Verdict: ACCEPTED

Test 56

Verdict: ACCEPTED

Test 57

Verdict: ACCEPTED

Test 58

Verdict: ACCEPTED

Test 59

Verdict: ACCEPTED

Test 60

Verdict: ACCEPTED

Test 61

Verdict: ACCEPTED

Test 62

Verdict: ACCEPTED

Test 63

Verdict: ACCEPTED

Test 64

Verdict: ACCEPTED

Test 65

Verdict: ACCEPTED

Test 66

Verdict: ACCEPTED

Test 67

Verdict: ACCEPTED

Test 68

Verdict: ACCEPTED

Test 69

Verdict: ACCEPTED

Test 70

Verdict: RUNTIME ERROR

Test 71

Verdict: RUNTIME ERROR

Test 72

Verdict: RUNTIME ERROR

Test 73

Verdict: RUNTIME ERROR

Test 74

Verdict: RUNTIME ERROR

Test 75

Verdict: ACCEPTED

Test 76

Verdict: RUNTIME ERROR

Test 77

Verdict: ACCEPTED

Test 78

Verdict: RUNTIME ERROR

Test 79

Verdict: ACCEPTED

Test 80

Verdict: RUNTIME ERROR

Test 81

Verdict: RUNTIME ERROR

Test 82

Verdict: RUNTIME ERROR

Test 83

Verdict: RUNTIME ERROR

Test 84

Verdict: RUNTIME ERROR

Test 85

Verdict: RUNTIME ERROR

Test 86

Verdict: ACCEPTED

Test 87

Verdict: ACCEPTED

Test 88

Verdict: RUNTIME ERROR

Test 89

Verdict: ACCEPTED