47 lines
1.3 KiB
Haskell
47 lines
1.3 KiB
Haskell
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-- 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 = 11
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type Pair = (Int, Int)
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type Input = [Pair]
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type Parser = Parsec Void String
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parseNumber :: Parser Int
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parseNumber = read <$> some digitChar <* optional hspace
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parsePair :: Parser Pair
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parsePair = (,) <$> parseNumber
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<*> parseNumber
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parseInput' :: Parser Input
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parseInput' = some (parsePair <* 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 compute'
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where
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(l, r) = unzip input
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compute' = fmap abs $ zipWith (-) (L.sort l) (L.sort r)
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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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