I find today’s task a bit fuzzy. I first considered shrinking the universe to the smallest possible perimeter. However, I wasn’t happy with that idea, because it’s possible that the universe expands (rather than shrinks) to the desired message (e.g. if all points are originally at (0, 0) and in the next step they expand to the message).

Therefore I opted for an approach where I look for the first occurrence of horizontally aligned clusters. In each step I compute the clusters, where each cluster consists of all neighbouring points. The algorithm stops when all the clusters have exactly the same vertical bounds (ymin, ymax).

Solution is available here and it finishes in about 4.5s.

Here’s my solution to Day 10:

https://github.com/JEG2/advent_of_code_2018/blob/master/day_10/the_stars_align.exs

I live streamed the creation of this. You can watch the video here (until it falls off Twitch 14 days from now):

After a weekend away from my computer I need to catch-up on the previous few puzzles but I decided to tackle today’s because it looked interesting (and involved outputting more than just an answer.

Unlike @sasajuric I decided to take a chance and assumed that the universe would contract to form the word and then expand so I check for when the next layout’s bounds are bigger to get the word (I really didn’t consider it expanding!). I suppose that the safe compromise might be to do the first adjustment and see if the universe expands or contracts and then follow that pattern.

Anyway, my code is here.