78 lines
2.1 KiB
Haskell
78 lines
2.1 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.Monad (void, when)
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import qualified Data.Set 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 System.Exit (die)
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exampleExpectedOutput = 4
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data Bag = Bag { name :: String
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, contents :: [(Int, String)]
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} deriving (Show)
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type Parser = Parsec Void String
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parseName :: Parser String
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parseName = do
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adjective <- some letterChar
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void (char ' ')
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color <- some letterChar
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return $ adjective ++ " " ++ color
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parseInt :: Parser Int
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parseInt = do
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i <- some digitChar
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return $ read i
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parseContent :: Parser (Int, String)
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parseContent = do
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i <- parseInt
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void (char ' ')
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name <- parseName
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void (string " bag")
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void (optional $ char 's')
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void (string ", " <|> string ".")
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return (i, name)
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parseContents :: Parser [(Int, String)]
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parseContents = some parseContent <|> (string "no other bags." *> return [])
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parseBag :: Parser Bag
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parseBag = do
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name <- parseName
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void $ string " bags contain "
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contents <- parseContents
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void (char '\n')
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return $ Bag { name=name, contents=contents }
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parseBags :: Parser [Bag]
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parseBags = some parseBag <* eof
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parseInput :: String -> IO [Bag]
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parseInput filename = do
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input <- readFile filename
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case runParser parseBags filename input of
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Left bundle -> die $ errorBundlePretty bundle
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Right bags -> return bags
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compute :: [Bag]-> Int
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compute bags = (length . compute' $ S.fromList ["shiny gold"]) - 1
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where
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bagsContaining :: S.Set String -> S.Set String
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bagsContaining s = S.union s $ S.fromList . (map name) $ filter (\x -> not . S.null . S.intersection s $ S.fromList . (map snd) . contents $ x) bags
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compute' :: S.Set String -> S.Set String
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compute' s = if s == s' then s else compute' s'
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where
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s' = bagsContaining s
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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) (die $ "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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