Advent of Code 2021 day 20

AoC_2021_20.py

TRANSLATION = str.maketrans({"#": "1", ".": "0"})


def index(y, x, img):
    bitstr = "".join(
        img[yy][xx] for yy in (y - 1, y, y + 1) for xx in (x - 1, x, x + 1)
    ).translate(TRANSLATION)
    return int(bitstr, 2)


def enhance(img, ch):
    extra = [[ch] * len(img[0])] * 2
    img_ext = [[ch, ch] + row + [ch, ch] for row in extra + img + extra]
    img_out = [
        [algo[index(ir, ic, img_ext)] for ic in range(1, len(img_ext[0]) - 1)]
        for ir in range(1, len(img_ext) - 1)
    ]
    ch_out = algo[index(1, 1, [[ch] * 3] * 3)]
    return img_out, ch_out


algo, chunk = open("input_20.txt").read().strip().split("\n\n")
image = [list(line) for line in chunk.splitlines()]

image, char = enhance(image, ".")
image, char = enhance(image, char)
print("part 1:", sum(row.count("#") for row in image))

for _ in range(48):
    image, char = enhance(image, char)
print("part 2:", sum(row.count("#") for row in image))