29 lines
1020 B
Haskell
29 lines
1020 B
Haskell
import AoC
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import Control.Applicative (empty)
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import Control.Monad.Zip (mzip)
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import Data.List (intercalate)
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import Data.Maybe (catMaybes)
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compose2 :: (a' -> b' -> c) -> (a -> a') -> (b -> b') -> a -> b -> c
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compose2 f g h x y = f (g x) (h y)
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(??) :: Functor f => f (a -> b) -> a -> f b
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f ?? x = fmap ($ x) f
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countHits :: (Int, Int) -> [[Bool]] -> Int
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countHits = length . filterMap lookup . catMaybes .: compose2 (zipWith mzip) maybeIndices justLines
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where justRightSteps = map (pure . Just) . enumFromThen 0
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downNothings = flip replicate Nothing . pred
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maybeIndices = uncurry $ compose2 (flip intercalate) justRightSteps downNothings
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justLines = map Just
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lookup = uncurry $ flip (!!)
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filterMap = filter id .: map
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treeCharToBool :: Char -> Bool
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treeCharToBool = (== '#')
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main = runAoC (map (cycle . map treeCharToBool) . lines) part1 part2
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where part1 = countHits (3, 1)
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part2 = product . (fmap countHits [(1,1), (3,1), (5,1), (7,1), (1,2)] ??)
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