Advent of code 2024 day 9 part 2 fast (18 ms)

def day9_part2(s):
  values = list(map(int, s.strip() + '0'))
  nums, skips = values[::2], values[1::2]
  positions = np.cumsum([0, 0] + values)[1::2]
  empty_index = [0] * 10  # First possible empty space of each size.

  checksum = 0
  for i1 in reversed(range(len(nums))):
    n = nums[i1]
    position = positions[i1]
    for i0 in range(empty_index[n], i1):
      if skips[i0] >= n:
        position = positions[i0 + 1] - skips[i0]
        skips[i0] -= n
        break
    empty_index[n] = i0
    for _ in range(n):
      checksum += position * i1
      position += 1

  return checksum