중복없는 조합을 만들어내는 프로그램의 알고리즘....

module Main where
 
import List
import IO
 
permutations n = permutationsOf [1..n]
permutations' n = [rotation k y | k <- [0..(n-1)],
                                  y <- [1:y | y <- permutationsOf [2..n]]]
permutations'' n = foldr (++) [] (take n perms)
          where
            perms = first:[rotations a | a <- perms]
            first = [1:y | y <- permutationsOf [2..n]]
            rotations a = [rotation 1 y | y <- a]
 
permutations''' n = super_permutations 1 n
 
super_permutations m n
          | m < n = foldr (++) [] (take (n-m+1) perms)
          | m == n = [ [n] ]
          | otherwise = error "m should be smaller than n"
          where
            perms = first:[rotations a | a <- perms]
            first = [m:y | y <- super_permutations (m+1) n]
            rotations a = [rotation 1 y | y <- a]
 
permutationsOf [] = [[]]
permutationsOf xs = [x:xs' | x <- xs, xs' <- permutationsOf (delete x xs)]
 
rotation 0 ys = ys
rotation k (y:ys) = rotation (k-1) (ys ++ [y])
 
main = do
  n <- getLine
  doShowList (permutations''' (read n))
 
doShowList [] = return ()
doShowList (x:xs) = do
                      putStrLn (show x)
                      doShowList xs

Prelude Main> length (permutations''' 10)
3628800
(2.58 secs, 243525992 bytes)
Prelude Main> length (permutations'' 10)
3628800
(4.36 secs, 428327028 bytes)
Prelude Main> length (permutations' 10)
3628800
(5.44 secs, 2372800716 bytes)
Prelude Main> length (permutations 10)
3628800
(5.10 secs, 2227579804 bytes)