Advent of code 2025 day 11

def day11(s, *, part2=False):
  # The solution assumes that the graph does not contain cycles!
  edges = {lhs: set(rhs.split()) for line in s.splitlines() for lhs, rhs in [line.split(': ')]}

  @functools.cache
  def get_count(node, num_special_visited):
    if node == 'out':
      return 1 if num_special_visited >= 2 else 0
    return sum(
        get_count(node2, num_special_visited + (node in {'dac', 'fft'}))
        for node2 in edges[node]
    )

  return get_count('svr', 0) if part2 else get_count('you', 2)