33 lines
1.3 KiB
Haskell
33 lines
1.3 KiB
Haskell
import Data.Char (isDigit)
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import Data.List (uncons)
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import Data.List.Split (splitOn, chunksOf)
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import Data.Matrix (Matrix, fromLists, toList, rref, zero)
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import Data.Either (fromRight)
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import Data.Maybe (mapMaybe, fromJust)
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isAlmostInt :: (RealFrac a) => a -> Bool
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isAlmostInt x = let diff = x - fromInteger (round x)
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in abs diff < 0.001
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getMatrix :: (Read a) => String -> Matrix a
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getMatrix s = let nValues = map (map read . splitOn ",") . splitOn ":" . drop 1 $ filter (\x -> isDigit x || x == ',' || x == ':') s
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eq1 = map (fst . fromJust . uncons) nValues
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eq2 = map last nValues
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in fromLists [eq1, eq2]
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solve :: (RealFrac a) => Matrix a -> Maybe [a]
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solve eqSystem = let rowEchelonList = toList . fromRight (zero 1 1) $ rref eqSystem
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solutions = [ rowEchelonList !! 2, rowEchelonList !! 5 ]
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in if all isAlmostInt solutions
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then Just solutions
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else Nothing
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cost :: [Int] -> Int
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cost [x, y] = 3 * x + y
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main = do
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contents <- map concat . chunksOf 4 . lines <$> readFile "day13.txt"
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let eqSystems = map getMatrix contents
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solutions = (map . map) round $ mapMaybe solve eqSystems
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print . sum $ map cost solutions
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