80 lines
3.2 KiB
Haskell
80 lines
3.2 KiB
Haskell
-- 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 = 140
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example2ExpectedOutput = 772
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example3ExpectedOutput = 1930
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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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compute :: Input -> Int
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compute input = fst $ V.ifoldl' compute' (0, M.empty) input
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where
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compute' :: (Int, Visited) -> Int -> Line -> (Int, Visited)
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compute' (acc, visited) y line = VU.ifoldl' (compute'' y) (acc, visited) line
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compute'' :: Int -> (Int, Visited) -> Int -> Char -> (Int, Visited)
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compute'' y acc@(cost, visited) x c = case M.lookup (x, y) visited of
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Just _ -> acc -- already processed
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Nothing -> let (area, perimeter, visited') = enclose c (0, 0, visited) (x, y) in (cost + area * perimeter, M.union visited visited')
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enclose :: Char -> (Int, Int, Visited) -> Coord -> (Int, Int, Visited)
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enclose c acc@(area, perimeter, visited) (x, y) = case M.lookup (x, y) visited of
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Just _ -> acc
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Nothing -> case input V.!? y of
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Just line -> case line VU.!? x of
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Just c' -> let n = neighbors visited c x y in L.foldl' (enclose c) (1 + area, 4 - length n + perimeter, M.insert (x, y) () visited) n
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Nothing -> (0, 0, visited)
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Nothing -> (0, 0, visited)
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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 -> Coord -> 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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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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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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