Advent of code 2024 day 7

def day7(s, part2=False):
  total = 0
  for line in s.splitlines():
    desired, *values = map(int, re.split(':? ', line))

    def count_digits(number):
      return 1 if number == 0 else math.floor(math.log10(abs(number))) + 1

    def can_eval(current, lst):
      if not lst:
        return current == desired
      if current > desired:  # Optional pruning speedup (from 2.9 s to 1.9 s).
        return False
      return (
          can_eval(current * lst[0], lst[1:])
          or can_eval(current + lst[0], lst[1:])
          or (part2 and can_eval(current * 10 ** count_digits(lst[0]) + lst[0], lst[1:]))
      )

    if can_eval(values[0], values[1:]):
      total += desired

  return total