Run-length encoding: Difference between revisions
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(Emacs Lisp: Count first, then character) |
(→Haskell: Added a variant expressed as a fold.) |
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<pre>W12B1W12B3W24B1W14 |
<pre>W12B1W12B3W24B1W14 |
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WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW |
WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWWWWWWWWWWWWBWWWWWWWWWWWWWW |
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True</pre> |
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===As a fold=== |
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<lang haskell>import Data.Bifunctor (first) |
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----------------------- RUN LENGTHS ---------------------- |
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runLengths :: String -> [(Int, Char)] |
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runLengths "" = [] |
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runLengths s = |
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let go c ("", xs) = ([c], xs) |
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go c (cs@(x : run), xs) |
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| c == x = (c : cs, xs) |
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| otherwise = ([c], (length cs, x) : xs) |
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in uncurry |
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(:) |
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( first |
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((,) . length <*> head) |
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(foldr go ("", []) s) |
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) |
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--------------------------- TEST ------------------------- |
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main :: IO () |
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main = do |
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let testString = |
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"WWWWWWWWWWWWBWWWWWWWWWWWWBBBWWWWWWWWWWWWWW" |
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<> "WWWWWWWWWWBWWWWWWWWWWWWWW" |
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encoded = runLengths testString |
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putStrLn $ showLengths encoded |
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print $ concatMap (uncurry replicate) encoded == testString |
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------------------------- DISPLAY ------------------------ |
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showLengths :: [(Int, Char)] -> String |
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showLengths [] = [] |
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showLengths ((n, c) : xs) = show n <> [c] <> showLengths xs</lang> |
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{{Out}} |
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<pre>12W1B12W3B24W1B14W |
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True</pre> |
True</pre> |
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