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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when)
import Data.List (foldl')
import qualified Data.Map as M
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import System.Exit (die)
exampleExpectedOutput = 32
exampleExpectedOutput2 = 126
data Bag = Bag { name :: String
, contents :: [(Int, String)]
} deriving (Show)
type Parser = Parsec Void String
parseName :: Parser String
parseName = do
adjective <- some letterChar
void (char ' ')
color <- some letterChar
return $ adjective ++ " " ++ color
parseInt :: Parser Int
parseInt = do
i <- some digitChar
return $ read i
parseContent :: Parser (Int, String)
parseContent = do
i <- parseInt
void (char ' ')
name <- parseName
void (string " bag")
void (optional $ char 's')
void (string ", " <|> string ".")
return (i, name)
parseContents :: Parser [(Int, String)]
parseContents = some parseContent <|> (string "no other bags." *> return [])
parseBag :: Parser Bag
parseBag = do
name <- parseName
void $ string " bags contain "
contents <- parseContents
void (char '\n')
return $ Bag { name=name, contents=contents }
parseBags :: Parser [Bag]
parseBags = some parseBag <* eof
parseInput :: String -> IO [Bag]
parseInput filename = do
input <- readFile filename
case runParser parseBags filename input of
Left bundle -> die $ errorBundlePretty bundle
Right bags -> return bags
compute :: [Bag]-> Int
compute bags = (compute' "shiny gold") - 1
where
bagsMap :: M.Map String Bag
bagsMap = foldl' (\acc b -> M.insert (name b) b acc) M.empty bags
compute' :: String -> Int
compute' s = foldl' (\acc (i, s') -> acc + i * (compute' s')) 1 (contents $ bagsMap M.! s)
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
example2 <- parseInput "example2"
let exampleOutput2 = compute example2
when (exampleOutput2 /= exampleExpectedOutput2) (die $ "example2 failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input
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