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authorJulien Dessaux2024-12-09 23:37:36 +0100
committerJulien Dessaux2024-12-09 23:37:36 +0100
commitcd08dcce0c50ab88b4900dffa2b0dba803d19643 (patch)
tree96713dae06d455b8eda54592586e46830e43ef0e /2024/09-Disk_Fragmenter/second.hs
parent2024-08 in haskell (diff)
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2024-09 in haskell
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+-- requires cabal install --lib megaparsec parser-combinators heap vector
+-- very slow with runghc, use ghc -O3 -o second second.hs and get the result in seconds
+module Main (main) where
+
+import Control.Monad (void, when)
+import qualified Data.List as L
+import Data.Maybe
+import qualified Data.Vector as V
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+exampleExpectedOutput = 2858
+
+type Input = [Int]
+
+type Parser = Parsec Void String
+
+parseBlockSize :: Parser Int
+parseBlockSize = read . pure <$> digitChar
+
+parseInput' :: Parser Input
+parseInput' = some parseBlockSize <* eol <* eof
+
+parseInput :: String -> IO Input
+parseInput filename = do
+ input <- readFile filename
+ case runParser parseInput' filename input of
+ Left bundle -> error $ errorBundlePretty bundle
+ Right input' -> return input'
+
+type Disk = V.Vector (Maybe Int) -- Maybe fileId
+type File = (Int, Int, Int) -- fileId, fileIndex, fileSize
+type Free = (Int, Int) -- index, size
+
+compute :: Input -> Int
+compute input = V.sum $ V.imap checksum defragmentedDisk
+ where
+ checksum _ Nothing = 0
+ checksum i (Just n) = i * n
+ defragmentedDisk :: Disk
+ (_, defragmentedDisk) = L.foldr defragment (frees, startingDisk) files
+ startingDisk :: Disk
+ startingDisk = V.replicate (sum input) Nothing
+ (files, frees, _, _) = computeFileIndexAndSize input ([], [], 0, 0)
+ computeFileIndexAndSize :: Input -> ([File], [Free], Int, Int) -> ([File], [Free], Int, Int)
+ computeFileIndexAndSize [] acc = acc
+ computeFileIndexAndSize (fileSize:[]) (files, frees, fileId, fileIndex) = (files ++ [(fileId, fileIndex, fileSize)], frees, 0, 0)
+ computeFileIndexAndSize (fileSize:freeSize:fs) (files, frees, fileId, fileIndex) = computeFileIndexAndSize fs
+ ( files ++ [(fileId, fileIndex, fileSize)]
+ , frees ++ [(fileIndex + fileSize, freeSize)]
+ , fileId + 1
+ , fileIndex + fileSize + freeSize )
+ defragment :: File -> ([Free], Disk) -> ([Free], Disk)
+ defragment (fileId, fileIndex, fileSize) (frees, disk) = (frees', disk V.// [(i, Just fileId)|i<-[fileIndex'..fileIndex'+fileSize-1]])
+ where
+ (fileIndex', frees') = findHole frees []
+ findHole :: [Free] -> [Free] -> (Int, [Free])
+ findHole [] _ = (fileIndex, frees)
+ findHole (f@(freeIndex, freeSize):fs) acc | freeIndex > fileIndex = (fileIndex, frees)
+ | freeSize == fileSize = (freeIndex, acc ++ fs)
+ | freeSize > fileSize = (freeIndex, acc ++ ((freeIndex + fileSize, freeSize - fileSize):fs))
+ | freeSize < fileSize = findHole fs (acc ++ [f])
+
+main :: IO ()
+main = do
+ example <- parseInput "example"
+ let exampleOutput = compute example
+ when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+ input <- parseInput "input"
+ print $ compute input