25 lines
1.1 KiB
Haskell
25 lines
1.1 KiB
Haskell
import Data.List ((\\))
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import Data.List.Split (splitOn)
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isSorted :: [(Int, Int)] -> [Int] -> Bool
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isSorted rules [x] = True
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isSorted rules (x:xs) = let after = [ p | (p, n) <- rules, n == x ]
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in not (any (`elem` after) xs) && isSorted rules xs
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getMiddle :: [Int] -> Int
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getMiddle xs = xs !! (length xs `div` 2)
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sortOnRules :: [(Int, Int)] -> [Int] -> [Int]
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sortOnRules _ [] = []
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sortOnRules rules (x:xs) = sortOnRules rules beforeArray ++ [x] ++ sortOnRules rules afterArray
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where afterArray = xs \\ before
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beforeArray = xs \\ afterArray
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before = [ p | (p, n) <- rules, n == x ]
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main = do
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contents <- map (splitOn "|") . lines <$> readFile "day5.txt"
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let rules = [ (read x, read y) | [x, y] <- takeWhile (/= [""]) contents ]
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unsorted = filter (not . isSorted rules) . map (map read) $ concatMap (map (splitOn ",")) . drop 1 $ dropWhile (/= [""]) contents
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fixUnsorted = map (sortOnRules rules) unsorted
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print . sum $ map getMiddle fixUnsorted
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