aoc2021-22.py

import re
import sys

# 3d regions represented as tuples of 3 tuples: ((x1, x2), (y1, y2), (z1, z2))


def valid(r):
    return all(c[0] <= c[1] for c in r)


def count_cubes(r):
    ret = 1
    for c in r:
        ret *= c[1] - c[0] + 1
    return ret


def count_cubes_init(r):
    INIT_REGION = tuple((-50, 50) for _ in range(3))
    if overlap(INIT_REGION, r):
        return count_cubes(common(INIT_REGION, r))
    else:
        return 0


def overlap(r1, r2):
    return all(c1[0] <= c2[1] and c1[1] >= c2[0] for c1, c2 in zip(r1, r2))


def common(r1, r2):
    return tuple((max(c1[0], c2[0]), min(c1[1], c2[1])) for c1, c2 in zip(r1, r2))


def differ(r1, r2):
    if not overlap(r1, r2):
        return [r1]

    common_ = common(r1, r2)

    regions = [
        ((common_[0][1] + 1, r1[0][1]), r1[1], common_[2]),
        ((r1[0][0], common_[0][0] - 1), r1[1], common_[2]),
        (common_[0], (common_[1][1] + 1, r1[1][1]), common_[2]),
        (common_[0], (r1[1][0], common_[1][0] - 1), common_[2]),
        (r1[0], r1[1], (common_[2][1] + 1, r1[2][1])),
        (r1[0], r1[1], (r1[2][0], common_[2][0] - 1)),
    ]

    return [r for r in regions if valid(r)]


STEPS = re.findall(
    r"(on|off) x=(-?[0-9]+)\.\.(-?[0-9]+),y=(-?[0-9]+)\.\.(-?[0-9]+),z=(-?[0-9]+)\.\.(-?[0-9]+)",
    sys.stdin.read(),
)

regions = []

for onoff, *coords in STEPS:
    x1, x2, y1, y2, z1, z2 = [int(c) for c in coords]
    region = ((x1, x2), (y1, y2), (z1, z2))

    # subtract from all existing regions
    regions = sum((differ(r, region) for r in regions), start=[])

    # if it's an "on" region, add it
    if onoff == "on":
        regions.append(region)


print("Step 1:", sum(count_cubes_init(r) for r in regions))
print("Step 2:", sum(count_cubes(r) for r in regions))