Day 24: Crossed Wires
Megathread guidelines
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FAQ
- What is this?: Here is a post with a large amount of details: https://programming.dev/post/6637268
- Where do I participate?: https://adventofcode.com/
- Is there a leaderboard for the community?: We have a programming.dev leaderboard with the info on how to join in this post: https://programming.dev/post/6631465
Haskell bits and pieces
The nice thing about Haskell’s laziness (assuming you use Data.Map rather than Data.Map.Strict) is that the laziness can do a ton of the work for you - you might’ve spotted a few Haskell solutions in earlier days’ threads that use this kind of trick (eg for tabling/memoisation). Here’s my evaluation function:
eval l = let v = l & Map.map (\case Const x -> x And a b -> v Map.! a && v Map.! b Or a b -> v Map.! a || v Map.! b Xor a b -> v Map.! a /= v Map.! b) in vFor part 2, we know what the graph should look like (it’s just a binary adder); I think this is a maximal common subgraph problem, but I’m still reading around that at the mo. I’d love to know if there’s a trick to this.
Thank you for showing this trick, I knew Haskell was lazy but this one blew my mind again.
Yeah, I remember when I saw this for the first time. It’s astonishing how powerful lazy evaluation can be at times.