45 lines
1.5 KiB
Haskell
45 lines
1.5 KiB
Haskell
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import Data.List.Split (splitOn)
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import Data.List (elemIndex, sortOn, groupBy)
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import Data.Monoid ((<>))
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import Data.Function (on)
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data Property = Property Int Int Int deriving (Eq, Ord)
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data Particle = Particle {
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position :: Property,
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velocity :: Property,
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acceleration :: Property
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}
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instance Monoid Property where
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mempty = Property 0 0 0
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Property x1 y1 z1 `mappend` Property x2 y2 z2 = Property (x1 + x2) (y1 + y2) (z1 + z2)
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distance :: Particle -> Int
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distance (Particle (Property x y z) _ _) = abs x + abs y + abs z
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updateParticle :: Int -> Particle -> Particle
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updateParticle t (Particle p v a) =
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Particle (p <> t *** v <> (t * t `div` 2) *** a) (v <> t *** a) a
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where n *** (Property x y z) = Property (n * x) (n * y) (n * z)
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stepParticles :: [Particle] -> [Particle]
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stepParticles particles =
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concat . filter ((== 1) . length) . groupBy ((==) `on` position) . sortOn position . map step $ particles
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where step (Particle p v a) = Particle (p <> v <> a) (v <> a) a
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parseProperty :: String -> Property
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parseProperty str =
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let x : y : z : [] = map read . splitOn "," . drop 3 . init $ str
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in Property x y z
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parseLine :: String -> Particle
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parseLine str =
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let p : v : a : [] = map parseProperty . splitOn ", " $ str
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in Particle p v a
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main :: IO ()
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main = do
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particles <- map parseLine . lines <$> readFile "20.txt"
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let distances = map (distance . updateParticle 400) particles
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print $ elemIndex (minimum distances) distances
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print $ length $ iterate stepParticles particles !! 40
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