Advent of code 2023 day 8 concise

def day8(s, *, part2=False):
  lines = s.splitlines()
  routes = {line[:3]: (line[7:10], line[12:15]) for line in lines[2:]}

  def length(node, end):
    for index, ch in enumerate(itertools.cycle(lines[0])):
      if node.endswith(end):
        return index
      node = routes[node][ch == 'R']

  if part2:
    return math.lcm(*(length(node, 'Z') for node in routes if node.endswith('A')))
  return length('AAA', 'ZZZ')