day11.py

#!/usr/bin/env python3

import sys
from copy import deepcopy

def occupied_neighbors(grid, r, c):
	deltas = (
		(-1, 0), ( 1,  0), (0, 1), ( 0, -1),
		(-1, 1), (-1, -1), (1, 1), ( 1, -1)
	)

	total = 0
	for dr, dc in deltas:
		rr, cc = r + dr, c + dc
		if 0 <= rr <= MAXROW and 0 <= cc <= MAXCOL:
			total += grid[rr][cc] == OCCUPIED

	return total

def occupied_in_sight(grid, r, c):
	deltas = (
		(-1, 0), ( 1,  0), (0, 1), ( 0, -1),
		(-1, 1), (-1, -1), (1, 1), ( 1, -1)
	)

	total = 0
	for dr, dc in deltas:
		rr, cc = r + dr, c + dc

		while 0 <= rr <= MAXROW and 0 <= cc <= MAXCOL:
			if grid[rr][cc] != FLOOR:
				if grid[rr][cc] == OCCUPIED:
					total += 1
				break

			rr += dr
			cc += dc

	return total

def evolve(grid, occ_counter, occ_threshold):
	while 1:
		previous = deepcopy(grid)

		for r, row in enumerate(previous):
			for c, cell in enumerate(row):
				if cell == FLOOR:
					continue

				occ = occ_counter(previous, r, c)

				if cell == EMPTY and occ == 0:
					grid[r][c] = OCCUPIED
				elif cell == OCCUPIED and occ >= occ_threshold:
					grid[r][c] = EMPTY

		if grid == previous:
			return sum(row.count(OCCUPIED) for row in grid)

		previous = grid


# Open the first argument as input or use stdin if no arguments were given
fin = open(sys.argv[1]) if len(sys.argv) > 1 else sys.stdin

original = list(map(list, map(str.rstrip, fin.readlines())))
MAXROW, MAXCOL = len(original) - 1, len(original[0]) - 1
OCCUPIED, EMPTY, FLOOR = '#L.'

total_occupied = evolve(deepcopy(original), occupied_neighbors, 4)
print('Part 1:', total_occupied)

total_occupied = evolve(deepcopy(original), occupied_in_sight, 5)
print('Part 2:', total_occupied)