Day 24: Crossed Wires
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View all comments 4 points
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 v
For 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.
2 points
Thank you for showing this trick, I knew Haskell was lazy but this one blew my mind again.
3 points
