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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
import Debug.Trace
exampleExpectedOutput = 30
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 -> Integer
compute = fst . L.foldl' compute' (0, L.repeat 1) . map score'
where
compute' :: (Integer, [Integer]) -> Int -> (Integer, [Integer])
compute' (acc, stack) score = (acc', stack')
where
copies = head stack
acc' = acc + copies
(scored, remain) = L.splitAt score $ tail stack
stack' = map (+ copies) scored ++ remain
score' :: Card -> Int
score' (Card _ winnings numbers) | wins == 0 = 0
| otherwise = wins
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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