53 lines
1.6 KiB
Haskell
53 lines
1.6 KiB
Haskell
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module Main where
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import System.Environment (getArgs)
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import Control.Monad (void)
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import Data.List (transpose)
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import Text.Parsec (parse, Parsec, endBy, many, char, anyChar, (<|>), try, string, lookAhead, getPosition, sourceName)
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import Text.Parsec.Char (oneOf)
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import Text.ParserCombinators.Parsec (eof)
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rows :: Parsec String () [String]
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rows = endBy (many $ oneOf "XMAS") (void $ char '\n') <* eof
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rotate90 :: [[a]] -> [[a]]
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rotate90 = reverse . transpose
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diagonals :: [[a]] -> [[a]]
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diagonals = (++)
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-- Lower half (excluding the main diagonal)
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<$> reverse . transpose . map reverse . zipWith take [1..] . drop 1
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-- Upper half
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<*> transpose . zipWith drop [0..]
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-- | counts the number of "XMAS" (as well as the backwards "SAMX") in the input
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countLineXMAS :: Parsec String () Int
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countLineXMAS =
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try (lookAhead (string "XMAS" <|> string "SAMX")
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>> anyChar >> (+1) <$> countLineXMAS)
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<|> (anyChar >> countLineXMAS)
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<|> (eof >> return 0)
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countAllXMAS :: Parsec String () Int
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countAllXMAS = do
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grid <- rows
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let linesOfInterest = grid ++ concatMap ($ grid) [transpose, diagonals, diagonals . rotate90]
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sName <- sourceName <$> getPosition
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counts <- mapM (either (\p -> fail $ "Parse Error! " ++ show p) return . parse countLineXMAS sName) linesOfInterest
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return $ sum counts
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part1 :: FilePath -> IO Int
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part1 fp = do
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content <- readFile fp
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case parse countAllXMAS fp content of
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Left e -> fail $ "Oh no! " ++ show e
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Right v -> return v
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main :: IO ()
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main = do
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args <- getArgs
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(fp:_) <- return args
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resPart1 <- part1 fp
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putStrLn $ "Solution (Part 1) : " ++ show resPart1
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