Day 4: Scratchcards


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  • Leo Uino@lemmy.sdf.org
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    11 months 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