day17.py

#!/usr/bin/env python3

from itertools import product
from copy import deepcopy

src = open("input.txt", "r").readlines()
# src = """
# .#.
# ..#
# ###""".splitlines()
src = [r.strip() for r in src if r.strip()]

sz = len(src)
dim = 4

dirs = list(product([-1, 0, 1], repeat=dim))
dirs.remove(tuple([0] * dim))

start = set()

for y, r in enumerate(src):
    for x, c in enumerate(r):
        if c == "#":
            if dim == 3:
                start.add((0, y, x))
            else:
                start.add((0, 0, y, x))


def adj(p):
    for d in dirs:
        if dim == 3:
            yield p[0] + d[0], p[1] + d[1], p[2] + d[2]
        else:
            yield p[0] + d[0], p[1] + d[1], p[2] + d[2], p[3] + d[3]


def inactives(points):
    s = set()

    for p in points:
        for a in adj(p):
            if a not in points:
                s.add(a)

    return s


def neighbors(p, points):
    n = 0
    for a in adj(p):
        if a in points:
            n += 1
            if n > 3:
                return n
    return n


def turn(points):
    cp = deepcopy(points)
    for p in points:
        if neighbors(p, points) not in [2, 3]:
            cp.remove(p)

    for p in inactives(points):
        if neighbors(p, points) == 3:
            cp.add(p)

    return cp


board = start
for _ in range(6):
    board = turn(board)

print(len(board))