Day 4: Scratchcards

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
  • Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ or pastebin (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)

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  • lwhjp
    4•1 year 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 <- map readCard . lines <$> readFile "input04"
  print $ part1 input
  print $ part2 input