75 lines
2.1 KiB
Haskell
75 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.Applicative.Permutations
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import Control.Monad (void, when)
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import Data.Char qualified as C
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import Data.Either
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import Data.Functor
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import Data.List qualified as L
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import Data.Map qualified as M
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import Data.Maybe
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import Data.Set qualified as S
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import Data.Vector qualified as V
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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 Debug.Trace
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exampleExpectedOutput = 21
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data Tile = Broken | Operational | Unknown deriving Eq
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instance Show Tile where
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show Broken = "#"
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show Operational = "."
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show Unknown = "?"
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data Row = Row [Tile] [Int] deriving Show
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type Input = [Row]
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type Parser = Parsec Void String
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parseNumber :: Parser Int
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parseNumber = read <$> some digitChar <* optional (char ',')
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parseTile :: Parser Tile
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parseTile = char '#' $> Broken
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<|> char '.' $> Operational
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<|> char '?' $> Unknown
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parseRow :: Parser Row
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parseRow = Row <$> some parseTile <* space
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<*> some parseNumber <* eol
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parseInput' :: Parser Input
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parseInput' = some parseRow <* eof
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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valid :: [Int] -> [Tile] -> Bool
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valid record tiles = map length (L.filter (L.any (/= Operational)) $ L.group tiles) == record
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permutations :: [Tile] -> [[Tile]]
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permutations [] = [[]]
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permutations (Unknown:xs) = permutations (Operational:xs) ++ permutations (Broken:xs)
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permutations (x:xs) = map (x:) $ permutations xs
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compute :: Input -> Int
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compute = sum . map compute'
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where
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compute' :: Row -> Int
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compute' (Row tiles record) = length . filter (valid record) $ permutations tiles
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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) (error $ "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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