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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when)
import Data.List qualified as L
import Data.Map qualified as M
import Data.Maybe (catMaybes)
import Data.Set qualified as S
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import System.Exit (die)
exampleExpectedOutput = 5
newtype Ingredient = Ingredient String deriving (Eq, Ord, Read, Show)
newtype Allergen = Allergen String deriving (Eq, Ord, Read, Show)
type Rule = ([Ingredient], [Allergen])
type Input = [Rule]
type Parser = Parsec Void String
parseRule :: Parser Rule
parseRule = do
ingredients <- some ((Ingredient <$> some letterChar) <* char ' ')
void $ string "(contains "
allergens <- some ((Allergen <$> some letterChar) <* optional (string ", "))
void $ string ")\n"
return $ (ingredients, allergens)
parseInput' :: Parser Input
parseInput' = some parseRule <* eof
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseInput' filename input of
Left bundle -> die $ errorBundlePretty bundle
Right input' -> return input'
compute :: Input -> Int
compute rules = sum . map count $ filter isUnused ingredients
where
ingredients :: [Ingredient]
ingredients = S.elems . S.fromList . concat $ map fst rules
candidates :: [[Ingredient]]
candidates = M.elems candidatesMap
candidatesMap :: M.Map Allergen [Ingredient]
candidatesMap = L.foldl' appendIngredientsForRule M.empty rules
appendIngredientsForRule :: M.Map Allergen [Ingredient] -> Rule -> M.Map Allergen [Ingredient]
appendIngredientsForRule m (is, as) = L.foldl' (appendIngredientsForAllergen is) m as
appendIngredientsForAllergen :: [Ingredient] -> M.Map Allergen [Ingredient] -> Allergen -> M.Map Allergen [Ingredient]
appendIngredientsForAllergen is m a = case M.lookup a m of
Nothing -> M.insert a is m
Just is' -> M.insert a (L.intersect is is') m
isUnused :: Ingredient -> Bool
isUnused i = (catMaybes $ map (L.elemIndex i) candidates) == []
count :: Ingredient -> Int
count i = sum $ map (length . L.elemIndices i) (map fst rules)
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input
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