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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Applicative.Permutations
import Control.Monad (void, when)
import Data.Char qualified as C
import Data.Either
import Data.List qualified as L
import Data.Map qualified as M
import Data.Maybe
import Data.Set qualified as S
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
exampleExpectedOutput = 13
data Card = Card Int [Int] [Int] deriving Show
type Input = [Card]
type Parser = Parsec Void String
parseNumber :: Parser Int
parseNumber = read <$> some digitChar <* many (char ' ')
parseCard :: Parser Card
parseCard = do
id <- string "Card" *> many (char ' ') *> parseNumber <* char ':' <* many (char ' ')
winnings <- some parseNumber
void $ char '|' <* many (char ' ')
numbers <- some parseNumber
return $ Card id winnings numbers
parseInput' :: Parser Input
parseInput' = some (parseCard <* 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 = sum . map compute'
where
compute' :: Card -> Int
compute' (Card _ winnings numbers) | wins == 0 = 0
| otherwise = 2 ^ (wins - 1)
where
wins = length $ winnings `L.intersect` numbers
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
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