encoding.hs.txt

Ulm大学2003-2004年竞赛题

-- Problem   Run Length Encoding
-- Algorithm Straight-Forward
-- Runtime   O(n)
-- Author    Walter Guttmann
-- Date      2003.12.07

main :: IO ()
main =
  do input <- readFile "encoding.in"
     mapM_ (putStrLn . solve) $ lines input

solve :: String -> String
solve "" = ""
solve xs@(y:ys) = if r > 1 then show r ++ [y] ++ solve (drop r xs)
                           else "1" ++ patch (take s xs) ++ "1" ++ solve (drop s xs)
  where r = min 9 $ length $ takeWhile (== y) xs
        s = length $ takeWhile (uncurry (/=)) $ zip xs (ys ++ "\n")
        patch = concatMap (\x -> if x == '1' then "11" else [x])