eldridge.cam
Advent of Code solutions
2021:9
+18
2021/9/p1.hs
+18
2021/9/p1.hs
···
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import Data.Array.Unboxed
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import Data.Char
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import Data.Maybe
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readGrid :: String -> Array (Int, Int) Int
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readGrid contents = listArray ((1, 1), (height, width)) $ concat input
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where
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input = fmap (fmap digitToInt) $ lines contents
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width = length $ input !! 0
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height = length input
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neighbours (y, x) = [(y - 1, x), (y + 1, x), (y, x + 1), (y, x - 1)]
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isMinPoint grid here = all (> (grid ! here)) $ mapMaybe (grid !?) (neighbours here)
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answer grid = sum $ fmap ((+ 1) . (grid !)) $ filter (isMinPoint grid) $ indices grid
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main = getContents >>= print . answer . readGrid
+29
2021/9/p2.hs
+29
2021/9/p2.hs
···
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import Data.Array.Unboxed
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import Data.Char
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import Data.Maybe
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import Data.List (sortBy)
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import Data.Set qualified as Set
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readGrid :: String -> Array (Int, Int) Int
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readGrid contents = listArray ((1, 1), (height, width)) $ concat input
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where
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input = fmap (fmap digitToInt) $ lines contents
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width = length $ input !! 0
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height = length input
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neighbours (y, x) = [(y - 1, x), (y + 1, x), (y, x + 1), (y, x - 1)]
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isMinPoint grid here = all (> (grid ! here)) $ mapMaybe (grid !?) (neighbours here)
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basin grid origin = basin_ Set.empty origin
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where
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basin_ :: Set.Set (Int, Int) -> (Int, Int) -> Set.Set (Int, Int)
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basin_ co here
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| not $ inRange (bounds grid) here = co
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| grid ! here == 9 = co
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| Set.member here co = co
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| otherwise = foldl basin_ (Set.insert here co) (neighbours here)
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answer grid = product $ take 3 $ sortBy (flip compare) $ fmap (Set.size . basin grid) $ filter (isMinPoint grid) $ indices grid
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main = getContents >>= print . answer . readGrid