Advent of code 2024 day 9 part 2 (slow)

def day9_part2(s):
  generator = enumerate(more_itertools.grouper(s.strip(), 2, 'fill', 0))
  pairs: list[tuple[list[int], int]] = [([index] * int(a), int(b)) for index, (a, b) in generator]

  i1 = len(pairs) - 1
  while i1:
    lst, skip = pairs[i1]
    n = len(lst)
    for i0 in range(i1):
      if pairs[i0][1] >= n:
        pairs = pairs[:i0] + [(pairs[i0][0], 0), (lst, pairs[i0][1] - n)] + pairs[i0 + 1 :]
        i1 += 1
        pairs[i1] = [], skip + n
        break
    i1 -= 1

  checksum = position = 0
  for lst, skip in pairs:
    for index in lst:
      checksum += position * index
      position += 1
    position += skip

  return checksum