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authorJulien Dessaux2024-12-01 11:40:32 +0100
committerJulien Dessaux2024-12-01 11:40:32 +0100
commite51c318b876a10be5a82f341e3d32e6050740a0c (patch)
tree022426af4321ca7bc06dba9ff708d2fce7f9a769 /2024/01-Historian_Hysteria/first.hs
parent2023-25 in haskell (diff)
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2024-01 in haskell
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+-- requires cabal install --lib megaparsec parser-combinators heap vector
+module Main (main) where
+
+import Control.Monad (void, when)
+import qualified Data.List as L
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+exampleExpectedOutput = 11
+
+type Pair = (Int, Int)
+type Input = [Pair]
+
+type Parser = Parsec Void String
+
+parseNumber :: Parser Int
+parseNumber = read <$> some digitChar <* optional hspace
+
+parsePair :: Parser Pair
+parsePair = (,) <$> parseNumber
+ <*> parseNumber
+
+parseInput' :: Parser Input
+parseInput' = some (parsePair <* 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'
+
+compute :: Input -> Int
+compute input = sum compute'
+ where
+ (l, r) = unzip input
+ compute' = fmap abs $ zipWith (-) (L.sort l) (L.sort r)
+
+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