39 lines
1004 B
Haskell
39 lines
1004 B
Haskell
import Data.List (elemIndex, tails)
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import Data.Maybe (fromJust)
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doLZW :: Eq a => [a] -> [a] -> [Int]
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doLZW _ [] = []
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doLZW as (x:xs) = lzw (return <$> as) [x] xs
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where
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lzw a w [] = [fromJust $ elemIndex w a]
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lzw a w (x:xs)
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| w_ `elem` a = lzw a w_ xs
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| otherwise = fromJust (elemIndex w a) : lzw (a ++ [w_]) [x] xs
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where
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w_ = w ++ [x]
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undoLZW :: [a] -> [Int] -> [a]
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undoLZW _ [] = []
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undoLZW a cs =
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cs >>=
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(!!)
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(foldl
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((.) <$> (++) <*>
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(\x xs -> return (((++) <$> head <*> take 1 . last) ((x !!) <$> xs))))
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(return <$> a)
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(take2 cs))
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take2 :: [a] -> [[a]]
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take2 xs = filter ((2 ==) . length) (take 2 <$> tails xs)
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main :: IO ()
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main = do
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print $ doLZW ['\0' .. '\255'] "TOBEORNOTTOBEORTOBEORNOT"
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print $
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undoLZW
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['\0' .. '\255']
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[84, 79, 66, 69, 79, 82, 78, 79, 84, 256, 258, 260, 265, 259, 261, 263]
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print $
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((==) <*> ((.) <$> undoLZW <*> doLZW) ['\NUL' .. '\255'])
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"TOBEORNOTTOBEORTOBEORNOT"
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