52 lines
2 KiB
Haskell
52 lines
2 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Monad (void, when)
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import qualified Data.List as L
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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exampleExpectedOutput = 1928
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type Input = [Int]
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type Parser = Parsec Void String
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parseBlockSize :: Parser Int
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parseBlockSize = read . pure <$> digitChar
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parseInput' :: Parser Input
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parseInput' = some parseBlockSize <* eol <* eof
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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compute :: Input -> Int
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compute input = sum $ map (\(x, y) -> x * y) $ zip [0..] $ computeFile files' free []
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where
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files = [s | (i,s)<-zip [0..] input, even i]
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files' = zip [0..] files
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free = [s | (i,s)<-zip [0..] input, odd i]
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computeFile :: [(Int, Int)] -> [Int] -> [Int] -> [Int]
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computeFile ((fId, fSize):fs) free acc = computeFillFree fs free (acc ++ L.replicate fSize fId)
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computeFillFree :: [(Int, Int)] -> [Int] -> [Int] -> [Int]
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computeFillFree [] _ acc = acc
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computeFillFree files (free:frees) acc | free == fSize = computeFile fs frees (acc ++ L.replicate fSize fId)
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| free > fSize = computeFillFree fs (free-fSize:frees) (acc ++ L.replicate fSize fId)
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| free < fSize = computeFile (fs++[(fId, fSize-free)]) frees (acc ++ L.replicate free fId)
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where
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(fId, fSize) = last files
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fs = init files
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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