Advent of Code Day 18 Follow-Up

In today's post, I came to the realization that I should have a little library to dealing with 3D coordinates and arrays easier.

I've now created such a library, and redid last night's challenge using it.

In the first challenge, just checking for exposed faces:

import "vector3"

if 0 then fname = "input.txt" else fname = "example.txt"
lines = file.readLines(fname)
if not lines[-1] then lines.pop

cubes = []
volume = list.init3d(21, 21, 21, 0)

for line in lines
    pos = line.split(",")
    pos.apply @val
    cubes.push pos
    volume.set pos, 1
end for

count = 0
for cube in cubes.values
    for n in vector3.neighbors6
        npos = cube.plus(n)
        if not volume.get(npos) then count = count + 1
    end for
end for
print "Faces: " + count

We now create a volume (3D array), initialized to 0, changed to 1 wherever we have a cube; we also keep cubes now as a list (not map) of 3D coordinates. Then we can just iterate over those cubes, checking the neighbors (using our handy new neighbors6 list), and add up how many faces are exposed.

Part 2 is really no harder. We just initialize our volume to value 2, meaning "interior space," and then after loading the cubes, do a floodFill from the origin to change all the outside space to 0. Then we don't need to change the counting loop at all.

import "vector3"

if 1 then fname = "input.txt" else fname = "example.txt"
lines = file.readLines(fname)
if not lines[-1] then lines.pop

cubes = []
// init volume to value 2, meaning "interior space"
volume = list.init3d(21, 21, 21, 2)

// load cubes
for line in lines
    pos = line.split(",")
    pos.apply @val
    cubes.push pos
    volume.set pos, 1
end for

// then flood-fill with 0, meaning "outside air"
volume.floodFill [0,0,0], 0

count = 0
for cube in cubes.values
    for n in vector3.neighbors6
        npos = cube.plus(n)
        if not volume.get(npos) then count = count + 1
    end for
end for
print "Faces: " + count

I'm quite happy with the new library; it really does make working with 3D coordinates and arrays a breeze. Here's hoping a need for that will come up again!