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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 = "mxmxvkd,sqjhc,fvjkl"
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 -> String
compute rules = L.intercalate "," . map (\(_, Ingredient i) -> i) $ M.assocs allergensMap
where
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
allergensMap :: M.Map Allergen Ingredient
allergensMap = allergensMap' candidatesMap M.empty
allergensMap' :: M.Map Allergen [Ingredient] -> M.Map Allergen Ingredient -> M.Map Allergen Ingredient
allergensMap' m acc
| M.size m == 0 = acc
| otherwise = allergensMap' (M.map (L.delete (head oneI)) $ M.delete oneK m) $ M.insert oneK (head oneI) acc
where
one = M.filter (\is -> length is == 1) m
(oneK, oneI) = head $ M.assocs one
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
|
