Advent of Code 2021 day 14 part 1

AoC_2021_14_1.py

"""
My solution for Advent of Code 2021 day 14 part 1.
"""
import re
from collections import Counter

with open("input_14.txt") as f:
    polym = list(f.readline().strip())
    rules = {
        tuple(pair): insert
        for pair, insert in re.findall(r"(..) -> (.)", f.read())
    }

for _ in range(10):
    nextgen = []
    for pair in zip(polym[:], polym[1:]):
        nextgen.append(pair[0])
        nextgen.append(rules[pair])
    nextgen.append(polym[-1])
    polym = nextgen

c = Counter(polym).most_common()
print(c[0][1] - c[-1][1])