Advent of code 2025 day 5

def day5(s, *, part2=False, unoptimized_part1=False):
  s_intervals, s_indices = s.split('\n\n')

  input_intervals = []
  for line in s_intervals.splitlines():
    start, end = map(int, line.split('-'))
    input_intervals.append((start, end + 1))

  indices = list(map(int, s_indices.splitlines()))

  # Sort the intervals and merge adjacent or overlapping intervals.
  intervals = []
  for start, stop in sorted(input_intervals):
    if not intervals or start > intervals[-1][1]:
      intervals.append((start, stop))
    elif stop > intervals[-1][1]:
      intervals[-1] = intervals[-1][0], stop

  if part2:
    return sum(stop - start for start, stop in intervals)

  if unoptimized_part1:
    return sum(any(start <= index < stop for start, stop in intervals) for index in indices)

  # Optimized Part 1.
  count = 0
  for index in indices:
    i = bisect.bisect_left(intervals, index, key=lambda interval: interval[0])
    if i > 0:
      start, stop = intervals[i - 1]
      count += start <= index < stop
  return count