Day 2: Red-Nosed Reports

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)
  • You can send code in code blocks by using three backticks, the code, and then three backticks or use something such as https://blocks.programming.dev if you prefer sending it through a URL

FAQ

  • lwhjp@lemmy.sdf.org
    1·
    3 months ago

    Haskell

    This was quite fun! I got a bit distracted trying to rewrite safe in point-free style, but I think this version is the most readable. There’s probably a more monadic way of writing lessOne as well, but I can’t immediately see it.

    safe xs = any gradual [diffs, negate <$> diffs]
  where
    diffs = zipWith (-) (drop 1 xs) xs
    gradual = all (`elem` [1 .. 3])

lessOne [] = []
lessOne (x : xs) = xs : map (x :) (lessOne xs)

main = do
  input :: [[Int]] <- map (map read . words) . lines <$> readFile "input02"
  print . length $ filter safe input
  print . length $ filter (any safe . lessOne) input
    • VegOwOtenks@lemmy.worldEnglish
      1·
      3 months ago

      Love to see your haskell solutions!

      I am so far very amazed with the compactness of your solutions, your lessOne is very much mind-Bending. I have never used or seen <$> before, is it a monadic $?

      Also I can’t seem to find your logic for this safety condition: The levels are either all increasing or all decreasing, did you figure that it wasn’t necessary?