73 lines
2.1 KiB
Haskell
73 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 Data.List (intersect, transpose)
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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 = 20899048083289
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type TileID = Int
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data Tile = Tile { tileID :: TileID
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, image :: [[Bool]]
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, edgesPermutations :: [[Bool]]
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} deriving Show
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type Input = [Tile]
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type Parser = Parsec Void String
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parseInt :: Parser Int
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parseInt = do
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n <- some digitChar
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return $ read n
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parseLine :: Parser [Bool]
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parseLine = do
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elts <- some (char '#' <|> char '.')
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void $ char '\n'
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return $ map (== '#') elts
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parseTile :: Parser Tile
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parseTile = do
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void $ string "Tile "
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n <- parseInt
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void $ string ":\n"
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image <- some parseLine
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let timage = transpose image
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edges = [head image, last image, head timage, last timage]
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inverted = map reverse edges
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return $ Tile n image (edges ++ inverted)
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parseInput' :: Parser Input
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parseInput' = do
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tiles <- some $ parseTile <* (optional $ char '\n')
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void eof
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return tiles
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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 -> die $ errorBundlePretty bundle
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Right input' -> return input'
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compute :: Input -> Int
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compute tiles = product . map fst . filter ((== 4) . snd) $ map matchingEdges tiles
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where
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matchingEdges :: Tile -> (TileID, Int)
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matchingEdges tile = (tileID tile, sum $ map (matches tile) tiles)
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matches :: Tile -> Tile -> Int
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matches Tile{tileID=a, image=_, edgesPermutations=e} Tile{tileID=b, image=_, edgesPermutations=f}
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| a == b = 0
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| otherwise = length $ intersect e f
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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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