66 lines
2.1 KiB
Haskell
66 lines
2.1 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators
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module Main (main) where
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import Control.Applicative.Permutations
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import Control.Monad (void, when)
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import Data.Char qualified as C
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import Data.Either
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import Data.List qualified as L
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import Data.Map qualified as M
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import Data.Maybe
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import Data.Set qualified as S
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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 = 35
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data Map = Map Int Int Int deriving Show -- destination source range
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data Mapping = Mapping String String [Map] deriving Show -- sourceStr destStr
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data Input = Input [Int] [Mapping] deriving Show -- seeds mappings
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type Parser = Parsec Void String
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parseNumber :: Parser Int
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parseNumber = read <$> some digitChar <* many (char ' ')
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parseMap :: Parser Map
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parseMap = Map <$> parseNumber
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<*> parseNumber
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<*> parseNumber <* eol
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parseMapping :: Parser Mapping
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parseMapping = Mapping <$> (some letterChar <* string "-to-")
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<*> (some letterChar <* string " map:" <* eol)
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<*> some parseMap <* optional eol
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parseInput' :: Parser Input
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parseInput' = Input <$> (string "seeds: " *> some parseNumber <* some eol)
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<*> some parseMapping <* 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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step :: [Map] -> Int -> Int
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step [] n = n
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step (Map dest src range:ms) n | n>=src && n<src+range = n - src + dest
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| otherwise = step ms n
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stepMapping :: [Int] -> Mapping -> [Int]
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stepMapping values (Mapping _ _ ms) = map (step ms) values
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compute :: Input -> Int
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compute (Input values mappings) = minimum $ L.foldl' stepMapping values mappings
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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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