Day 18 - Advent of Code 2016

""" day_18_01_02.py """

# usage: python3 day_18_01_02.py 40 < input
# usage: python3 day_18_01_02.py 400000 < input

import sys


situations = [['^', '.', '.'], ['^', '^', '.'], ['.', '.', '^'], ['.', '^', '^']]

rows = int(sys.argv[1])
row = ['.'] + list(input()) + ['.']

count = row.count('.')
for _ in range(rows - 1):
    prev = row
    row = ['.' for _ in prev]
    for i in range(1, len(prev)):
        if prev[i - 1:i + 2] in situations:
            row[i] = '^'
    count += row.count('.')

print(count - 2 * rows)