part2.py

# From user gabrielchl on Reddit
#
# cubes is a list of cubes that are on, all cubes in 
# this list is non-overlapping.
# When handling on or off commands, I loop through cubes, 
# if a cube overlaps the new cube to add or the "new 
# cube" to remove, I break the existing cube down into 
# smaller non-overlapping cubes and add those cubes back
# to cubes.

import re

input = re.findall(r'(on|off) x=(-?\d+)..(-?\d+),y=(-?\d+)..(-?\d+),z=(-?\d+)..(-?\d+)', open('input.txt').read())
cubes = []

for step in input:
    step = [int(x) if x.strip('-').isnumeric() else x for x in step]
    [op, ux, vx, uy, vy, uz, vz] = step
    for cubes_i in range(len(cubes)):
        [ux2, vx2, uy2, vy2, uz2, vz2] = cubes[cubes_i]
        if ux > vx2 or vx < ux2 or uy > vy2 or vy < uy2 or uz > vz2 or vz < uz2: # new on zone not overlapping existing on zone
            continue
        cubes[cubes_i] = None
        if ux > ux2:
            cubes.append((ux2, ux - 1, uy2, vy2, uz2, vz2))
        if vx < vx2:
            cubes.append((vx + 1, vx2, uy2, vy2, uz2, vz2))
        if uy > uy2:
            cubes.append((max(ux2, ux), min(vx2, vx), uy2, uy - 1, uz2, vz2))
        if vy < vy2:
            cubes.append((max(ux2, ux), min(vx2, vx), vy + 1, vy2, uz2, vz2))
        if uz > uz2:
            cubes.append((max(ux2, ux), min(vx2, vx), max(uy2, uy), min(vy2, vy), uz2, uz - 1))
        if vz < vz2:
            cubes.append((max(ux2, ux), min(vx2, vx), max(uy2, uy), min(vy2, vy), vz + 1, vz2))
    if op == 'on':
        cubes.append((min(ux, vx), max(ux, vx), min(uy, vy), max(uy, vy), min(uz, vz), max(uz, vz)))
    cubes = [cube for cube in cubes if cube is not None]

on_count = 0
for cube in cubes:
    [ux, vx, uy, vy, uz, vz] = cube
    on_count += (vx - ux + 1) * (vy - uy + 1) * (vz - uz + 1)
print(on_count)