Snakeless path

from collections import deque


def find_snakeless_path(n, snake_edges):
    forbidden = [set() for _ in range(n + 1)]
    for a, b in snake_edges:
        forbidden[a].add(b)
        forbidden[b].add(a)

    unvisited = set(range(2, n + 1))
    parent = [-1] * (n + 1)

    queue = deque([1])

    while queue:
        u = queue.popleft()

        to_visit = []
        for v in unvisited:
            if v not in forbidden[u]:
                to_visit.append(v)

        for v in to_visit:
            unvisited.remove(v)
            parent[v] = u
            queue.append(v)
            if v == n:
                queue.clear()
                break

    if parent[n] == -1:
        print(0)
        return

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

    print(len(path))
    print(" ".join(map(str, path)))


if __name__ == "__main__":
    n, m = map(int, input().split())
    snakes = []
    for i in range(m):
        start, end = map(int, input().split())
        snakes.append((start, end))

    find_snakeless_path(n, snakes)

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