61 lines
1.8 KiB
Haskell
61 lines
1.8 KiB
Haskell
import Data.List (transpose)
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import Data.List.Split (splitOn, chunksOf)
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import Data.HashMap (Map, insert, empty, (!))
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type Rules = Map String String
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squareRoot = floor . sqrt . fromIntegral
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validTwos = [
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[0..3],
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[0, 2, 1, 3],
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[1, 0, 3, 2],
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[1, 3, 0, 2],
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[2, 0, 3, 1],
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[2, 3, 0, 1],
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[3, 1, 2, 0],
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[3,2..0]
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]
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validThrees = [
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[0..8],
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[0, 3, 6, 1, 4, 7, 2, 5, 8],
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[2, 1, 0, 5, 4, 3, 8, 7, 6],
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[2, 5, 8, 1, 4, 7, 0, 3, 6],
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[6, 3, 0, 7, 4, 1, 8, 5, 2],
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[6, 7, 8, 3, 4, 5, 0, 1, 2],
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[8, 5, 2, 7, 4, 1, 6, 3, 0],
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[8,7..0]
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]
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valids :: String -> [String]
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valids str = map (map (str !!)) $ case length str of
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4 -> validTwos
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9 -> validThrees
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chunk :: String -> [[String]]
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chunk str =
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let size = squareRoot $ length str
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multiple = if even size then 2 else 3
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makeRow = map concat . transpose . map (chunksOf multiple) . chunksOf size
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in map makeRow $ chunksOf (size * multiple) str
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dechunk :: [[String]] -> String
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dechunk rows =
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let multiple = squareRoot . length . head . head $ rows
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unmakeRow = concat . concat . transpose . map (chunksOf multiple)
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in concat $ map unmakeRow rows
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enhance :: Rules -> String -> String
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enhance rules = dechunk . map (map (rules !)) . chunk
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parseLine :: String -> Rules -> Rules
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parseLine line =
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let input : output : [] = splitOn " => " $ filter (/= '/') line
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in flip (foldr (\key currRules -> insert key output currRules)) $ valids input
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main :: IO ()
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main = do
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rules <- foldr parseLine empty . lines <$> readFile "21.txt"
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let iterations = map (length . filter (=='#')) $ iterate (enhance rules) ".#...####"
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print $ iterations !! 5
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print $ iterations !! 18 |