47 lines
1.4 KiB
Haskell
47 lines
1.4 KiB
Haskell
module Day9_1 where
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import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
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import Data.Char (digitToInt)
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import Data.List (sort)
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-- i gave up on my original solution
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-- this isn't very original and is influcenced by other people's solutions
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-- i'm sorry
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columns :: String -> Int
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columns str = maximum $ map length $ lines str
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xy :: Int -> Int -> [[Int]] -> (Int, Int) -> Int
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xy w h arr (x, y)
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| x < 0 || x >= w = 9
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| y < 0 || y >= h = 9
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| otherwise = arr !! y !! x
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-- left, right, up, down from current coord
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neigh :: (Int, Int) -> [(Int, Int)]
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neigh (x, y) = [(x - 1, y), (x + 1, y), (x, y - 1), (x, y + 1)]
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basin :: Int -> Int -> [[Int]] -> [(Int, Int)] -> [(Int, Int)] -> [(Int, Int)]
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basin w h ints acc [] = acc
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basin w h ints acc (x:xs)
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| pos x == 9 || x `elem` acc = basin w h ints acc xs
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| otherwise = basin w h ints (x:acc) (xs ++ neigh x)
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where pos = xy w h ints
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main :: IO ()
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main = do
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input <- openFile "inputs/9.txt" ReadMode
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contents <- hGetContents input
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let ints = map (map digitToInt) $ lines contents
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let width = columns contents
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let height = length ints
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let coordMap = [ (x, y) | x <- [0..width-1], y <- [0..height-1] ]
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let pos = xy width height ints
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let lowest = [ coord | coord <- coordMap, and [neighbor > pos coord | neighbor <- pos <$> neigh coord] ]
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print . product . take 3 . reverse . sort $ map (length . basin width height ints [] . pure) lowest
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hClose input |