Day 15: Lens Library

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/ , pastebin, or github (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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  • Leo Uino
    3•1 year ago

    Haskell

    Took a while to figure out what part 2 was all about. Didn’t have the energy to golf this one further today, so looking forward to seeing the other solutions!

    Solution

    0.3 line-seconds

    import Data.Char
import Data.List
import Data.List.Split
import qualified Data.Vector as V

hash :: String -> Int
hash = foldl' (\a c -> ((a + ord c) * 17) `rem` 256) 0

hashmap :: [String] -> Int
hashmap = focus . V.toList . foldl' step (V.replicate 256 [])
  where
    focus = sum . zipWith focusBox [1 ..]
    focusBox i = sum . zipWith (\j (_, z) -> i * j * z) [1 ..] . reverse
    step boxes s =
      let (label, op) = span isLetter s
          i = hash label
       in case op of
            ['-'] -> V.accum (flip filter) boxes [(i, (/= label) . fst)]
            ('=' : z) -> V.accum replace boxes [(i, (label, read z))]
    replace ls (n, z) =
      case findIndex ((== n) . fst) ls of
        Just j ->
          let (a, _ : b) = splitAt j ls
           in a ++ (n, z) : b
        Nothing -> (n, z) : ls

main = do
  input <- splitOn "," . head . lines <$> readFile "input15"
  print $ sum . map hash $ input
  print $ hashmap input