Codeforces 208A - A. Dubstep

208A - A. Dubstep

• WUBを空白に置き換える
• 連続する空白をひとつの空白にまとめる
• 両端の空白を取り除く

-- "WUB"を取り除く(代わりに空白をおく)
removeWUB :: String -> String
removeWUB "" = ""
removeWUB ('W':'U':'B':xs) = ' ' : removeWUB xs
removeWUB (c:xs) = c : removeWUB xs

-- 連続する空白を一つにまとめる
packContinuousSpaces :: String -> String
packContinuousSpaces "" = ""
packContinuousSpaces xxs@(' ':' ':xs) = packContinuousSpaces $ tail xxs
packContinuousSpaces (x:xs) = x : packContinuousSpaces xs

trim :: String -> String
trim s = reverse $ trim' $ reverse $ trim' s
  where
    trim' (' ':xs) = trim' xs
    trim' s = s
   
calc = trim . packContinuousSpaces . removeWUB

main = do s <- getLine
          putStrLn $ calc s

trimするときにreverseが2回必要なのは仕方がないのかな…。