app/cses1622.hs

   1 import Data.List (sort, inits, tails, nub)
   2
   3 main :: IO ()
   4 main = do
   5   line1 <- getLine
   6   let base = sort line1
   7   let perms = permutations base
   8   print $ length perms
   9   putStrLn $ unlines perms
  10
  11 permutations :: String -> [String]
  12
  13 permutations [] = []
  14 permutations (x:[]) = [[x]]
  15 permutations xs = concatMap (\(y, ys) -> map (y:) (permutations ys)) (selects xs)
  16
  17 selects :: String -> [(Char, String)]
  18 selects [] = []
  19 selects xs = nub [(head t, h ++ (tail t))
  20                  | (h, t) <- zip (inits xs) (tails xs)
  21                  , not (null t)]
  22