Day 6: Wait for It


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)

FAQ

  • Leo Uino@lemmy.sdf.org
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    edit-2
    11 months ago

    Haskell

    This problem has a nice closed form solution, but brute force also works.

    (My keyboard broke during part two. Yet another day off the bottom of the leaderboard…)

    import Control.Monad
    import Data.Bifunctor
    import Data.List
    
    readInput :: String -> [(Int, Int)]
    readInput = map (\[t, d] -> (read t, read d)) . tail . transpose . map words . lines
    
    -- Quadratic formula
    wins :: (Int, Int) -> Int
    wins (t, d) =
      let c = fromIntegral t / 2 :: Double
          h = sqrt (fromIntegral $ t * t - 4 * d) / 2
       in ceiling (c + h) - floor (c - h) - 1
    
    main = do
      input <- readInput <$> readFile "input06"
      print $ product . map wins $ input
      print $ wins . join bimap (read . concatMap show) . unzip $ input