33 lines
953 B
Haskell
33 lines
953 B
Haskell
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import Linear.V2
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import Data.List
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import Control.Lens
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type Rope = (V2 Int,V2 Int)
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main :: IO ()
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main = do
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input <- concat <$> map (parse . words) <$> lines <$> readFile "input"
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print $ length $ nub $ sort $ snd $ moveAll ((V2 0 0,V2 0 0),[]) input
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parse :: [String] -> [V2 Int]
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parse (dir:len:[])
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| dir == "R" = f $ V2 1 0
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| dir == "L" = f $ V2 (-1) 0
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| dir == "U" = f $ V2 0 1
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| dir == "D" = f $ V2 0 (-1)
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where f = take (read len) . repeat
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moveAll :: (Rope,[V2 Int]) -> [V2 Int] -> (Rope,[V2 Int])
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moveAll r (x:xs) = moveAll (move r x) xs
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moveAll ((head,tail),xs) _ = ((head,tail),tail:xs)
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move :: (Rope,[V2 Int]) -> V2 Int -> (Rope,[V2 Int])
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move ((head,tail),ps) m = ((head+m,newTail),tail:ps)
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where newTail = tailMove (head + m - tail) + tail
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tailMove (V2 a b) = V2 (f a) (f b)
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where f x
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| abs a == abs b = 0
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| abs a + abs b == 1 = 0
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| otherwise = if abs x >= 2 then x `div` 2 else x
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