DailyProgrammer Challenge Solution (Sad Cycles)

c-unhappy.hs

import Control.Applicative
import Data.Char
import Data.List

iterateU f (x:xs) | x `elem` xs = x : (reverse $ takeWhile (/= x) xs)
                  | otherwise   = iterateU f $ f x : x : xs

main = do power <- read <$> getLine
          num <- getLine
          putStrLn $ intercalate ", " $
              (iterateU (show . foldl1 (+) .
               map ((^ power) . digitToInt)) . (:[])) num