this post was submitted on 09 Dec 2024
0 points (NaN% liked)

Advent Of Code

981 readers
21 users here now

An unofficial home for the advent of code community on programming.dev!

Advent of Code is an annual Advent calendar of small programming puzzles for a variety of skill sets and skill levels that can be solved in any programming language you like.

AoC 2024

Solution Threads

M T W T F S S
1
2 3 4 5 6 7 8
9 10 11 12 13 14 15
16 17 18 19 20 21 22
23 24 25

Rules/Guidelines

Relevant Communities

Relevant Links

Credits

Icon base by Lorc under CC BY 3.0 with modifications to add a gradient

console.log('Hello World')

founded 1 year ago
MODERATORS
[email protected]
[email protected]
[email protected]
0
๐Ÿ’ฟ - 2024 DAY 9 SOLUTIONS -๐Ÿ’ฟ (programming.dev)
submitted 2 weeks ago* (last edited 2 weeks ago) by [email protected] to c/[email protected]
43 comments fedilink hide all child comments
 

Day 9: Disk Fragmenter

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://topaz.github.io/paste/ if you prefer sending it through a URL

FAQ

you are viewing a single comment's thread
view the rest of the comments
[โ€“] [email protected] 0 points 2 weeks ago (1 children)

Haskell

Not a lot of time to come up with a pretty solution today; sorry.

import Data.List
import Data.Maybe
import Data.Sequence (Seq)
import Data.Sequence qualified as Seq

readInput :: String -> Seq (Maybe Int, Int)
readInput =
  Seq.fromList
    . zip (intersperse Nothing $ map Just [0 ..])
    . (map (read . singleton) . head . lines)

expand :: Seq (Maybe Int, Int) -> [Maybe Int]
expand = concatMap (uncurry $ flip replicate)

compact :: Seq (Maybe Int, Int) -> Seq (Maybe Int, Int)
compact chunks =
  case Seq.spanr (isNothing . fst) chunks of
    (suffix, Seq.Empty) -> suffix
    (suffix, chunks' Seq.:|> file@(_, fileSize)) ->
      case Seq.breakl (\(id, size) -> isNothing id && size >= fileSize) chunks' of
        (_, Seq.Empty) -> compact chunks' Seq.>< file Seq.<| suffix
        (prefix, (Nothing, gapSize) Seq.:<| chunks'') ->
          compact $ prefix Seq.>< file Seq.<| (Nothing, gapSize - fileSize) Seq.<| chunks'' Seq.>< (Nothing, fileSize) Seq.<| suffix

part1, part2 :: Seq (Maybe Int, Int) -> Int
part1 input =
  let blocks = dropWhileEnd isNothing $ expand input
      files = catMaybes blocks
      space = length blocks - length files
      compacted = take (length files) $ fill blocks (reverse files)
   in sum $ zipWith (*) [0 ..] compacted
  where
    fill (Nothing : xs) (y : ys) = y : fill xs ys
    fill (Just x : xs) ys = x : fill xs ys
part2 = sum . zipWith (\i id -> maybe 0 (* i) id) [0 ..] . expand . compact

main = do
  input <- readInput <$> readFile "input09"
  print $ part1 input
  print $ part2 input
[โ€“] [email protected] 0 points 2 weeks ago* (last edited 2 weeks ago) (1 children)

Second attempt! I like this one much better.

Edit: down to 0.040 secs now!

import Control.Arrow
import Data.Either
import Data.List
import Data.Map (Map)
import Data.Map qualified as Map

type Layout = ([(Int, (Int, Int))], Map Int Int)

readInput :: String -> Layout
readInput =
  map (read . singleton) . head . lines
    >>> (scanl' (+) 0 >>= zip) -- list of (pos, len)
    >>> zipWith ($) (intersperse Right [Left . (id,) | id <- [0 ..]])
    >>> partitionEithers
    >>> filter ((> 0) . snd . snd) *** Map.filter (> 0) . Map.fromAscList

checksum :: Layout -> Int
checksum = sum . map (\(id, (pos, len)) -> id * len * (2 * pos + len - 1) `div` 2) . fst

compact :: (Int -> Int -> Bool) -> Layout -> Layout
compact select (files, spaces) = foldr moveFile ([], spaces) files
  where
    moveFile file@(fileId, (filePos, fileLen)) (files, spaces) =
      let candidates = Map.assocs $ fst . Map.split filePos $ spaces
       in case find (select fileLen . snd) candidates of
            Just (spacePos, spaceLen) ->
              let spaces' = Map.delete spacePos spaces
               in if spaceLen >= fileLen
                    then
                      ( (fileId, (spacePos, fileLen)) : files,
                        if spaceLen == fileLen
                          then spaces'
                          else Map.insert (spacePos + fileLen) (spaceLen - fileLen) spaces'
                      )
                    else
                      moveFile
                        (fileId, (filePos + spaceLen, fileLen - spaceLen))
                        ((fileId, (spacePos, spaceLen)) : files, spaces')
            Nothing -> (file : files, spaces)

main = do
  input <- readInput <$> readFile "input09"
  mapM_ (print . checksum . ($ input) . compact) [const $ const True, (<=)]
[โ€“] [email protected] 0 points 2 weeks ago (1 children)

It will always be a wonder to me how you manage to do so much in so few lines, even your naive solution only takes a few seconds to run. ๐Ÿคฏ

[โ€“] [email protected] 0 points 2 weeks ago (1 children)

Aww, thank you <3

It's just practice, I guess? (The maths degree probably doesn't hurt either)

[โ€“] [email protected] 0 points 2 weeks ago

Maths degree at least explains the choice of language