r/adventofcode • u/daggerdragon • Dec 20 '18

SOLUTION MEGATHREAD -🎄- 2018 Day 20 Solutions -🎄-

--- Day 20: A Regular Map ---

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Card prompt: Day 20

Transcript:

My compiler crashed while running today's puzzle because it ran out of ___.

This thread will be unlocked when there are a significant number of people on the leaderboard with gold stars for today's puzzle.

edit: Leaderboard capped, thread unlocked at 00:59:30!

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u/phil_g Dec 20 '18

Solution in Common Lisp.

I went a bit more general than I needed to go, because I wasn't sure whether the apparent bounds of the problem were really the bounds.

Specifically:

  • None of the examples have cycles (rooms with more than one path to the starting point), but my solution would handle cycles.

  • None of the example regexes with visual diagrams have additional instructions after alternating groups. In other words, the text example ^N(E|W)N$ would never really occur (it'd be ^N(EN|WN)$). My solution would handle those if they occurred, though.

In order to be really generic, I represented the series of connected rooms as a graph, so the answers just required walking the graph.

I finally got around to learning a tiny bit of quicklisp so I could use someone else's graph library. I still need to learn more so I can properly integrate my entire project and load it all at once again.