Snakeless path

import sys
from collections import deque


def main():
    input = list(map(int, sys.stdin.buffer.read().split()))
    n, m = input[0], input[1]

    s = [set() for _ in range(n + 1)]
    j = 2
    for _ in range(m):
        a, b = input[j], input[j + 1]
        s[a].add(b)
        s[b].add(a)
        j+=2

    parent = [0] * (n + 1)
    parent[1] = -1
    queue = deque([1])

    next_vertex = list(range(1, n + 2))
    previous_vertex = list(range(-1, n))
    head = 2
    next_vertex[0] = 0
    previous_vertex[head] = 0

    while queue and parent[n] == 0:
        current = queue.popleft()
        vertex = head

        while vertex <= n:
            next_unvisited = next_vertex[vertex]
            if vertex not in s[current]:
                parent[vertex] = current
                queue.append(vertex)

                if previous_vertex[vertex] == 0:
                    head = next_unvisited
                else:
                    next_vertex[previous_vertex[vertex]] = next_unvisited
                if next_unvisited <= n:
                    previous_vertex[next_unvisited] = previous_vertex[vertex]

            vertex = next_unvisited

    if parent[n] == 0:
        print(0)
        return

    path = []
    vertex = n
    while vertex != -1:
        path.append(vertex+1)
        vertex = parent[vertex]
    path.reverse()

    print(len(path))
    print(*path)


if __name__ == "__main__":
    main()

Test 1

Verdict: ACCEPTED

Test 2

Verdict: WRONG ANSWER

Test 3

Verdict: WRONG ANSWER

Test 4

Verdict: WRONG ANSWER

Test 5

Verdict: WRONG ANSWER

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: WRONG ANSWER

Test 9

Verdict: ACCEPTED

Test 10

Verdict: WRONG ANSWER

Test 11

Verdict: WRONG ANSWER

Test 12

Verdict: WRONG ANSWER

Test 13

Verdict: WRONG ANSWER

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: WRONG ANSWER

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: WRONG ANSWER

Test 21

Verdict: WRONG ANSWER

Test 22

Verdict: WRONG ANSWER

Test 23

Verdict: WRONG ANSWER

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: WRONG ANSWER

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: WRONG ANSWER

Test 31

Verdict: WRONG ANSWER

Test 32

Verdict: WRONG ANSWER

Test 33

Verdict: WRONG ANSWER

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED

Test 36

Verdict: WRONG ANSWER

Test 37

Verdict: ACCEPTED

Test 38

Verdict: ACCEPTED

Test 39

Verdict: ACCEPTED

Test 40

Verdict: WRONG ANSWER

Test 41

Verdict: WRONG ANSWER

Test 42

Verdict: WRONG ANSWER

Test 43

Verdict: WRONG ANSWER

Test 44

Verdict: ACCEPTED

Test 45

Verdict: ACCEPTED

Test 46

Verdict: WRONG ANSWER

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: WRONG ANSWER

Test 51

Verdict: WRONG ANSWER

Test 52

Verdict: WRONG ANSWER

Test 53

Verdict: WRONG ANSWER

Test 54

Verdict: WRONG ANSWER

Test 55

Verdict: ACCEPTED

Test 56

Verdict: WRONG ANSWER

Test 57

Verdict: ACCEPTED

Test 58

Verdict: WRONG ANSWER

Test 59

Verdict: ACCEPTED

Test 60

Verdict: WRONG ANSWER

Test 61

Verdict: ACCEPTED

Test 62

Verdict: ACCEPTED

Test 63

Verdict: WRONG ANSWER

Test 64

Verdict: WRONG ANSWER

Test 65

Verdict: WRONG ANSWER

Test 66

Verdict: ACCEPTED

Test 67

Verdict: ACCEPTED

Test 68

Verdict: WRONG ANSWER

Test 69

Verdict: ACCEPTED

Test 70

Verdict: WRONG ANSWER

Test 71

Verdict: WRONG ANSWER

Test 72

Verdict: WRONG ANSWER

Test 73

Verdict: WRONG ANSWER

Test 74

Verdict: WRONG ANSWER

Test 75

Verdict: ACCEPTED

Test 76

Verdict: WRONG ANSWER

Test 77

Verdict: ACCEPTED

Test 78

Verdict: WRONG ANSWER

Test 79

Verdict: ACCEPTED

Test 80

Verdict: WRONG ANSWER

Test 81

Verdict: ACCEPTED

Test 82

Verdict: ACCEPTED

Test 83

Verdict: WRONG ANSWER

Test 84

Verdict: WRONG ANSWER

Test 85

Verdict: WRONG ANSWER

Test 86

Verdict: ACCEPTED

Test 87

Verdict: ACCEPTED

Test 88

Verdict: WRONG ANSWER

Test 89

Verdict: ACCEPTED