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