45 lines
1.4 KiB
Haskell
45 lines
1.4 KiB
Haskell
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module Main where
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import System.Environment (getArgs)
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import Data.Maybe (mapMaybe)
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import Text.Parsec (parse, Parsec, endBy, sepBy1, char, newline, many)
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import Text.ParserCombinators.Parsec.Number (decimal)
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type PageOrdering = (Int, Int)
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type PagesUpdate = [Int]
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printInfo :: Parsec String () ([PageOrdering], [PagesUpdate])
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printInfo = (,) <$> orderings <*> (newline *> pagesUpdates) <* many (char '\n')
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where
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pagesUpdates :: Parsec String () [PagesUpdate]
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pagesUpdates = endBy (sepBy1 decimal $ char ',') newline
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orderings :: Parsec String () [PageOrdering]
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orderings = endBy ((,) <$> decimal <*> (char '|' *> decimal)) $ char '\n'
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allDependencies :: [a] -> [(a, a)]
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allDependencies (h:tl) = map (flip (,) h) tl ++ allDependencies tl
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allDependencies [] = []
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middleElement :: [a] -> Maybe a
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middleElement [] = Nothing
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middleElement [a] = Just a
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middleElement (_:h':tl) = case reverse (h':tl) of
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(_:middle) -> middleElement middle
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[] -> Nothing
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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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(requiredOrderings, pagesUpdates) <- either (fail . show) return $ parse printInfo fp content
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let wellOrdered = filter (all (`notElem` requiredOrderings) . allDependencies) pagesUpdates
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return $ sum $ mapMaybe middleElement wellOrdered
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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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