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-rw-r--r--2023/22-Sand_Slabs/second.hs125
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diff --git a/2023/22-Sand_Slabs/second.hs b/2023/22-Sand_Slabs/second.hs
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+-- requires cabal install --lib megaparsec parser-combinators heap vector
+module Main (main) where
+
+import Control.Applicative.Permutations
+import Control.Monad (void, when)
+import qualified Data.Char as C
+import Data.Either
+import Data.Functor
+import qualified Data.Heap as H
+import qualified Data.List as L
+import qualified Data.Map as M
+import Data.Maybe
+import qualified Data.Set as S
+import qualified Data.Vector as V
+import qualified Data.Vector.Unboxed as VU
+import Data.Void (Void)
+import Text.Megaparsec
+import Text.Megaparsec.Char
+
+import Debug.Trace
+
+exampleExpectedOutput = 7
+
+type Coord = (Int, Int, Int)
+data Brick = Brick Coord Coord deriving (Eq, Show)
+instance Ord Brick where
+ (Brick (_, _, z1) (_, _, z2)) `compare` (Brick (_, _, c1) (_, _, c2)) = min z1 z2 `compare` min c1 c2
+type Input = [Brick]
+
+type Parser = Parsec Void String
+
+parseNumber :: Parser Int
+parseNumber = read <$> some digitChar <* optional (char ',')
+
+parseCoord :: Parser Coord
+parseCoord = (,,) <$> parseNumber
+ <*> parseNumber
+ <*> parseNumber
+
+parseBrick :: Parser Brick
+parseBrick = Brick <$> parseCoord <* char '~'
+ <*> parseCoord <* eol
+
+parseInput' :: Parser Input
+parseInput' = some parseBrick <* eof
+
+parseInput :: String -> IO Input
+parseInput filename = do
+ input <- readFile filename
+ case runParser parseInput' filename input of
+ Left bundle -> error $ errorBundlePretty bundle
+ Right input' -> return input'
+
+type Height = (Int, Maybe Int) -- (Height, BrickId that achieved that height - 1)
+type HeightMap = V.Vector (V.Vector Height)
+type SupportMap = M.Map Int [Int] -- BrickId -> [supports brickIds]
+
+compute :: Input -> Int
+compute input = sum $ map howManyWouldFallIf $ L.filter (isSupportBrick supportMap) $ [0..(length input - 1)]
+ where
+ howManyWouldFallIf :: Int -> Int
+ howManyWouldFallIf brickId = length . snd $ removeFalling (supportMap, []) [brickId]
+ where
+ removeFalling :: (SupportMap, [Int]) -> [Int] -> (SupportMap, [Int])
+ removeFalling acc@(sm, l) f | supportBricks == [] = acc
+ | otherwise = removeFalling (sm', l ++ supportBricks) supportBricks
+ where
+ removeOne :: SupportMap -> Int -> SupportMap
+ removeOne sm i = M.map (L.delete i) $ M.delete i sm
+ sm' :: SupportMap
+ sm' = L.foldl' removeOne sm f
+ supportBricks :: [Int]
+ supportBricks = L.filter unsupported $ M.keys sm'
+ where
+ unsupported :: Int -> Bool
+ unsupported i = sm' M.! i == [] && let (Brick (_, _, z) _) = settledInput L.!! i in z > 1
+ isSupportBrick :: SupportMap -> Int -> Bool
+ isSupportBrick sm brickId = L.any isSoleSupport $ M.elems sm
+ where
+ isSoleSupport :: [Int] -> Bool
+ isSoleSupport [l] = brickId == l
+ isSoleSupport _ = False
+ (_, settledInput, heightMap, supportMap) = L.foldl' settle (0, [], startingHeightMap, M.empty) startingInput
+ where
+ settle :: (Int, Input, HeightMap, SupportMap) -> Brick -> (Int, Input, HeightMap, SupportMap)
+ settle (brickId, acc, hm, sm) (Brick (x1, y1, z1) (x2, y2, z2)) = (brickId+1, acc ++ [(Brick (a1, b1, height) (a2, b2, height-c1+c2))], hm', sm')
+ where
+ (a1, a2, b1, b2, c1, c2) = (min x1 x2, max x1 x2, min y1 y2, max y1 y2, min z1 z2, max z1 z2)
+ (height, supports) = V.foldl' heightLine (0, []) (V.ifilter (\i _ -> i>= b1 && i <= b2) hm)
+ where
+ heightLine :: (Int, [Int]) -> V.Vector Height -> (Int, [Int]) -- height, [support]
+ heightLine acc line = V.foldl' heightElt acc (V.ifilter (\i _ -> i >= a1 && i <= a2) line)
+ where
+ heightElt :: (Int, [Int]) -> Height -> (Int, [Int])
+ heightElt a@(hacc, _) (1, Nothing) | hacc > 1 = a
+ | otherwise = (1, [])
+ heightElt a@(hacc, sacc) (h, Just p) | hacc == h = (hacc, if elem p sacc then sacc else p:sacc)
+ | hacc > h = a
+ | otherwise = (h, [p])
+ hm' = V.imap updateLine hm
+ where
+ updateLine :: Int -> V.Vector Height -> V.Vector Height
+ updateLine y line | y < b1 || y > b2 = line
+ | otherwise = V.imap updateElt line
+ where
+ updateElt :: Int -> Height -> Height
+ updateElt x z | x < a1 || x > a2 = z
+ | otherwise = (height+c2-c1+1, Just brickId)
+ sm' = M.insert brickId supports sm
+ startingHeightMap = V.replicate (ymax+1) (V.replicate (xmax+1) (1, Nothing))
+ where
+ (xmax, ymax) = L.foldl' findBounds (xs, ys) input -- xmin and ymin are 0 for both example and input
+ where
+ Brick (xs, ys, _) _ = head input
+ findBounds :: (Int, Int) -> Brick -> (Int, Int)
+ findBounds (a, b) (Brick (x1, y1, _) (x2, y2, _)) = (maximum [a, x1, x2], maximum [b, y1, y2])
+ startingInput = L.sort input
+
+main :: IO ()
+main = do
+ example <- parseInput "example"
+ let exampleOutput = compute example
+ when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
+ input <- parseInput "input"
+ print $ compute input