60 lines
1.7 KiB
Haskell
60 lines
1.7 KiB
Haskell
module Day8.Main where
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import System.IO
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import Data.List
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main :: IO ()
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main = do
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putStrLn "Day 8"
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handle <- openFile "app/Day8/input" ReadMode
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contents <- hGetContents handle
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let r1 = part1 contents
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putStrLn $ "part 1: " ++ show r1
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let r2 = part2 contents
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putStrLn $ "part 2: " ++ show r2
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type Tree = (Int,[Int],[Int],[Int],[Int]) -- Self, N, E, S, W
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enumerate :: [a] -> [(Int, a)]
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enumerate = zip [0..]
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parseData :: String -> [[Int]]
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parseData contents = (map . map) (read . singleton :: Char -> Int) $ lines contents
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toTrees :: [[Int]] -> [Tree]
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toTrees rows = [(tree, north r c, east r c, south r c, west r c) | (r, line) <- enumerate rows, (c, tree) <- enumerate line]
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where
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columns = transpose rows
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east r c = drop (c + 1) $ rows !! r
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west r c = reverse $ take c $ rows !! r
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north r c = reverse $ take r $ columns !! c
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south r c = drop (r + 1) $ columns !! c
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isVisible :: Int -> [Int] -> Bool
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isVisible _ [] = True
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isVisible t ts = all (< t) ts
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invisibleFromOutside :: Tree -> Bool
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invisibleFromOutside (t,n,e,s,w) = all (not . isVisible t) [n,e,s,w]
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part1 :: String -> Int
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part1 = length . filter (not . invisibleFromOutside) . toTrees . parseData
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-- Includive version of takeWhile (because lentgh takeWhile + 1 doesn't work for when the outer border is the reason you can't see further)
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takeWhileI :: (a -> Bool) -> [a] -> [a]
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takeWhileI _ [] = []
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takeWhileI p (x:xs) =
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x : if p x then takeWhileI p xs else []
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viewingDistance :: Int -> [Int] -> Int
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viewingDistance t ts = length $ takeWhileI (< t) ts
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scenicScore :: Tree -> Int
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scenicScore (t,n,e,s,w) = product $ map (viewingDistance t) [n,e,s,w]
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part2 :: String -> Int
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part2 = maximum . map scenicScore . toTrees . parseData
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