47259d1697
We look at each valid (having coordinates inside the grid) neighbor to a cell including a paper roll and then see if the neighbor contains a roll of paper or not. Finally we count the number of rolls, if it is less than 4 we can pick it.
66 lines
1.6 KiB
Haskell
66 lines
1.6 KiB
Haskell
module Main where
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import Data.Map (Map)
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import qualified Data.Map as M
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import System.Environment (getArgs)
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main :: IO ()
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main = do
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input <- readFile . head =<< getArgs
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print $ part1 input
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print $ part2 input
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part1 :: String -> Int
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part1 s = length $ filter (canPickRoll m) (M.keys m)
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where
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m = grid s
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grid :: String -> Map (Int, Int) Bool
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grid = M.fromList . concat . map (\(c, l) -> zipWith (\r ch -> ((r, c), ch == '@')) [0 ..] l) . zip [0 ..] . lines
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canPickRoll :: Map (Int, Int) Bool -> (Int, Int) -> Bool
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canPickRoll m p
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| m M.! p = checkNeighbor m p
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| otherwise = False
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where
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checkNeighbor :: Map (Int, Int) Bool -> (Int, Int) -> Bool
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checkNeighbor m' = (< 4) . length . filter (m' M.!) . filter (validPos gridSize) . neighbors
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neighbors :: (Int, Int) -> [(Int, Int)]
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neighbors (r, c) =
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[ (r + 1, c + 1),
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(r + 1, c),
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(r + 1, c - 1),
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(r, c + 1),
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(r, c - 1),
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(r - 1, c + 1),
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(r - 1, c),
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(r - 1, c - 1)
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]
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validPos :: (Int, Int) -> (Int, Int) -> Bool
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validPos (nr, nc) (r, c) = r >= 0 && r < nr && c >= 0 && c < nc
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gridSize :: (Int, Int)
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gridSize = duplicate . round . sqrt @Double . fromIntegral . M.size $ m
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duplicate :: a -> (a, a)
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duplicate a = (a, a)
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part2 :: String -> Int
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part2 = error "Not implemented"
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testInput :: String
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testInput =
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unlines
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[ "..@@.@@@@.",
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"@@@.@.@.@@",
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"@@@@@.@.@@",
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"@.@@@@..@.",
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"@@.@@@@.@@",
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".@@@@@@@.@",
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".@.@.@.@@@",
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"@.@@@.@@@@",
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".@@@@@@@@.",
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"@.@.@@@.@."
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]
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