Snakeless path

import math
import sys
sys.setrecursionlimit(10**8)

def find_path(s, f, visited=None, path=None):
    global g, n
    if visited is None:
        visited = [False] * n
    if path is None:
        path = []

    path.append(s)
    visited[s] = True

    if s == f:
        return path

    for i, w in enumerate(g[s]):
        if not visited[i] and w > 0:
            res_path = find_path(i, f, visited=visited, path=path.copy())
            if res_path:
                return res_path

    return None


n, m = map(int, input().split())
g = [[1 for _ in range(n)] for _ in range(n)]
paths = []
for i in range(m):
    a, b = map(int, input().split())
    g[a - 1][b - 1] = 0
    g[b - 1][a - 1] = 0

path = find_path(0, n - 1)

if path:
    print(len(path))
    for v in path:
        print(v + 1, end=' ')
    print()
else:
    print(0)

Test 1

Verdict: ACCEPTED

Test 2

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Verdict: RUNTIME ERROR