100 lines
4.6 KiB
Haskell
100 lines
4.6 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Monad (void, when)
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import qualified Data.List as L
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import qualified Data.Map as M
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import qualified Data.Vector as V
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import qualified Data.Vector.Unboxed as VU
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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example1ExpectedOutput = 80
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example2ExpectedOutput = 436
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example3ExpectedOutput = 1206
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example4ExpectedOutput = 236
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example5ExpectedOutput = 368
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type Line = VU.Vector Char
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type Input = V.Vector Line
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type Parser = Parsec Void String
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parseLine :: Parser Line
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parseLine = do
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line <- some letterChar <* eol
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return $ VU.generate (length line) (line !!)
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parseInput' :: Parser Input
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parseInput' = do
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line <- some parseLine <* eof
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return $ V.generate (length line) (line !!)
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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type Coord = (Int, Int)
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type Visited = M.Map Coord ()
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type Region = [Coord]
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compute :: Input -> Int
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compute input = sum $ map (\r -> corners r * length r) regions
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where
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(regions, _) = V.ifoldl' regions' ([], M.empty) input
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regions' :: ([Region], Visited) -> Int -> Line -> ([Region], Visited)
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regions' acc y line = VU.ifoldl' (regions'' y) acc line
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regions'' :: Int -> ([Region], Visited) -> Int -> Char -> ([Region], Visited)
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regions'' y acc@(rs, visited) x c = case M.lookup (x, y) visited of
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Just _ -> acc -- already processed
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Nothing -> let (r, visited') = flood c ([], visited) (x, y) in (r:rs, visited')
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flood :: Char -> (Region, Visited) -> (Int, Int) -> (Region, Visited)
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flood c acc@(rs, visited) (x, y) = case M.lookup (x, y) visited of
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Just _ -> acc
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Nothing -> L.foldl' (flood c) ((x, y):rs, M.insert (x, y) () visited) $ neighbors visited c x y
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neighbors :: Visited -> Char -> Int -> Int -> [Coord]
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neighbors visited c x y = filter (valid visited c) [ (x-1, y), (x+1, y), (x, y-1), (x, y+1) ]
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valid :: Visited -> Char -> (Int, Int) -> Bool
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valid visited c (x, y) = case input V.!? y of
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Just line -> case line VU.!? x of
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Just c' -> c == c'
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Nothing -> False
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Nothing -> False
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corners :: Region -> Int
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corners r = sum $ map corners' r
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where
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inside c = L.elem c r
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outside = not . inside
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corners' (x, y) = length $ filter id [ outside (x-1, y) && outside (x, y-1) -- top left in
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, outside (x+1, y) && outside (x, y-1) -- top right in
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, outside (x-1, y) && outside (x, y+1) -- bottom left in
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, outside (x+1, y) && outside (x, y+1) -- bottom right in
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, inside (x-1, y) && outside (x-1, y-1) && inside (x, y-1) -- top left out
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, inside (x+1, y) && outside (x+1, y-1) && inside (x, y-1) -- top right out
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, inside (x-1, y) && outside (x-1, y+1) && inside (x, y+1) -- bottom left out
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, inside (x+1, y) && outside (x+1, y+1) && inside (x, y+1) ] -- bottom right out
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main :: IO ()
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main = do
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example1 <- parseInput "example1"
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let exampleOutput = compute example1
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when (exampleOutput /= example1ExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show example1ExpectedOutput)
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example2 <- parseInput "example2"
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let exampleOutput = compute example2
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when (exampleOutput /= example2ExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show example2ExpectedOutput)
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example4 <- parseInput "example4"
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let exampleOutput = compute example4
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when (exampleOutput /= example4ExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show example4ExpectedOutput)
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example5 <- parseInput "example5"
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let exampleOutput = compute example5
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when (exampleOutput /= example5ExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show example5ExpectedOutput)
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example3 <- parseInput "example3"
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let exampleOutput = compute example3
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when (exampleOutput /= example3ExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show example3ExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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