41 lines
797 B
Haskell
41 lines
797 B
Haskell
import Control.Lens
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import Control.Monad
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import Data.List
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import Linear.V2
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import Linear.V3
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import Linear.V4
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import Linear.Vector
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main :: IO ()
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main = do
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input <- lines <$> readFile "input"
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let a = toVec input
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_ = a :: [V4 Int]
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print $ day17 a
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day17 = length . flip (!!) 6 . iterate step
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toVec input =
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[ zero & _xy .~ V2 x y
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| (y, line) <- zip [0 ..] input
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, (x, c) <- zip [0 ..] line
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, c == '#'
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]
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step state =
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(nub .
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concatMap fst .
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filter f . ap zip (map length) . group . sort . updateNeighbours)
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state
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where
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f (x, n) = n == 3 || n == 2 && head x `elem` state
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updateNeighbours = concatMap f
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where
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f coord =
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[ coord + v
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| v <-
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filter (/= zero) $
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nub $ map sum $ subsequences (ap (++) (map negate) basis)
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]
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