Day 9: Mirage Maintenance

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
    1•9 months ago

    Haskell

    I was expecting something much harder! Worried about tomorrow’s puzzle, now…

    diffs :: [Int] -> [[Int]]
diffs = takeWhile (not . all (== 0)) . iterate (zipWith (-) . tail <*> id)

part1 = sum . map last . diffs

part2 = head . scanr1 (-) . map head . diffs

main = do
  input <- map (map read . words) . lines <$> readFile "input09"
  print $ sum $ map part1 input
  print $ sum $ map part2 input