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