14_1.py

   1 """ Pair insertion """
   2 import collections
   3
   4 insertion_rules = {}
   5
   6 with open("14_input.txt") as f:
   7     polymer_template = f.readline().strip()
   8     f.readline()
   9
  10     for line in f:
  11         pair, insert = line.strip().split(" -> ")
  12
  13         insertion_rules[pair] = insert
  14
  15 extended_template = []
  16
  17 expected_length = len(polymer_template)
  18
  19 for gen in range(10):
  20     for i in range(len(polymer_template) - 1):
  21
  22         pair = polymer_template[i:i+2]
  23         extended_template += [
  24             polymer_template[i],
  25             insertion_rules[pair],
  26         ]
  27
  28     polymer_template = "".join(
  29         extended_template + [polymer_template[i + 1]]
  30     )
  31     extended_template = []
  32     expected_length += expected_length - 1
  33
  34     assert len(polymer_template) == expected_length, "Length unexpected"
  35
  36 letter_count = collections.defaultdict(int)
  37 for letter in polymer_template:
  38     letter_count[letter] += 1
  39
  40 print(max(letter_count.values()) - min(letter_count.values()))