70 lines
2 KiB
Haskell
70 lines
2 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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import Debug.Trace
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exampleExpectedOutput = 30
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data Card = Card Int [Int] [Int] deriving Show
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type Input = [Card]
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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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parseCard :: Parser Card
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parseCard = do
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id <- string "Card" *> many (char ' ') *> parseNumber <* char ':' <* many (char ' ')
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winnings <- some parseNumber
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void $ char '|' <* many (char ' ')
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numbers <- some parseNumber
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return $ Card id winnings numbers
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parseInput' :: Parser Input
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parseInput' = some (parseCard <* 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 -> Integer
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compute = fst . L.foldl' compute' (0, L.repeat 1) . map score'
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where
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compute' :: (Integer, [Integer]) -> Int -> (Integer, [Integer])
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compute' (acc, stack) score = (acc', stack')
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where
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copies = head stack
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acc' = acc + copies
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(scored, remain) = L.splitAt score $ tail stack
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stack' = map (+ copies) scored ++ remain
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score' :: Card -> Int
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score' (Card _ winnings numbers) | wins == 0 = 0
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| otherwise = wins
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where
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wins = length $ winnings `L.intersect` numbers
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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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