44 lines
1.5 KiB
Haskell
44 lines
1.5 KiB
Haskell
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module Main (main) where
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import Control.Monad (when)
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import Data.List (foldl')
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import Data.Maybe (mapMaybe)
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import qualified Data.Map as M
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import System.Exit (die)
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exampleExpectedOutput = 37
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type Seating = M.Map (Int, Int) Bool
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inputToList :: String -> [((Int, Int), Bool)]
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inputToList = snd . foldl' nextSeat ((0, 0), [])
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where
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nextSeat :: ((Int, Int), [((Int, Int), Bool)]) -> Char -> ((Int, Int), [((Int, Int), Bool)])
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nextSeat ((x, y), acc) '\n' = ((0, y+1), acc)
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nextSeat ((x, y), acc) '.' = ((x+1, y), acc)
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nextSeat ((x, y), acc) 'L' = ((x+1, y), acc ++ [((x, y), False)])
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parseInput :: String -> IO Seating
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parseInput filename = do
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input <- readFile filename
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return $ M.fromList (inputToList input)
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compute :: Seating -> Int
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compute seating
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| seating == seating' = length $ M.filter id seating
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| otherwise = compute seating'
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where
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seating' = M.mapWithKey next seating
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next :: (Int, Int) -> Bool -> Bool
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next (x, y) False = around (x, y) == []
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next (x, y) True = length (around (x,y)) < 4
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around :: (Int, Int) -> [Bool]
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around (x, y) = filter id $ mapMaybe (\v -> M.lookup v seating) [(x-1, y-1), (x, y-1), (x+1, y-1), (x-1, y), (x+1, y), (x-1, y+1), (x, y+1), (x+1, y+1)]
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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