Day 4: Scratchcards

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[-] lwhjp@lemmy.sdf.org 4 points 2 years ago

Haskell

11:39 -- I spent most of the time reading the scoring rules and (as usual) writing a parser...

import Control.Monad
import Data.Bifunctor
import Data.List

readCard :: String -> ([Int], [Int])
readCard =
  join bimap (map read) . second tail . break (== "|") . words . tail . dropWhile (/= ':')

countShared = length . uncurry intersect

part1 = sum . map ((\n -> if n > 0 then 2 ^ (n - 1) else 0) . countShared)

part2 = sum . foldr ((\n a -> 1 + sum (take n a) : a) . countShared) []

main = do
  input &lt;- map readCard . lines &lt;$> readFile "input04"
  print $ part1 input
  print $ part2 input

[-] sjmulder@lemmy.sdf.org 2 points 2 years ago

Still trying to make sense of it but that part two fold is just jummy!

[-] soulsource@discuss.tchncs.de 2 points 2 years ago

I'm really impressed by your part 2. And I thought my solution was short...

[-] lwhjp@lemmy.sdf.org 2 points 2 years ago

Not familiar with Lean4 but it looks like the same approach. High five!

this post was submitted on 04 Dec 2023

24 points (100.0% liked)

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