09.py

"""--- Day 9: Explosives in Cyberspace ---"""

def recurse(chomp, recurse_level, recurse_once):

  if recurse_once and recurse_level > 0:
    return len(chomp)

  i = length = 0
  while i < len(chomp):
    if chomp[i] == "(":
      rb = chomp.find(")", i)
      marker = chomp[i+1:rb]
      count, multi = [int(x) for x in marker.split("x")]
      length += multi * recurse(chomp[rb+1:rb+1+count], recurse_level+1, recurse_once)
      i = rb + count + 1 # skip over "(AxB)..."
    elif chomp[i] == "\n":
      i += 1
    else:
      length += 1
      i += 1

  return length

with open("input/09.txt", "r") as f:

  part1 = part2 = 0

  for instruction in f:
    part1 += recurse(instruction, 0, True)
    part2 += recurse(instruction, 0, False)

  print(part1)
  print(part2)