day_12.py

import collections
import re

def nextg(cur, recipe):
  start = min(cur)
  end = max(cur)
  x = set()

  for i in xrange(start - 3, end + 4):
    pat = ''.join('#' if i + k in cur else '.' for k in [-2, -1, 0, 1, 2])
    if pat in recipe:
      x.add(i)

  return x

def viz(cur):
  print ''.join('#' if i in cur else '.' for i in xrange(-5, 120))

#with open('day12test.txt') as f:
with open('files/day_12_input.txt') as f:
  lines = [l.rstrip('\n') for l in f]
  print lines

  init = lines[0][len('initial state: '):]
  recipe = set()
  for l in lines[2:]:
    if l[-1] == '#':  # I forgot this line the first time around.
      recipe.add(l[:5]) 

  cur = set(i for i, c in enumerate(init) if c == '#')

#   Part 1:
#   for i in xrange(20):
#     cur = nextg(cur, recipe)
#   print sum(cur)

  # Part 2:
  ls = 0
  # viz(cur)
  for i in xrange(2000):
    cur = nextg(cur, recipe)
    # viz(cur)
    s = sum(cur)
    # print i, s, s - ls
    ls = s
  print sum(cur)