[Haskell-cafe] warning - Euler problem spoiler enclosed

[Barbara Shirtcliff]

Hi,

In the following solution to problem 24, why is nub ignored?
I.e. if you do lexOrder of "0012," you get twice as many permutations as with "012," even though I have used nub.

puzzled,
Bar

-- file Euler.hs

module Euler where
import Data.List

{-

problem 24

A permutation is an ordered arrangement of objects. For example, 3124
is one possible permutation of the digits 1, 2, 3 and 4. If all of the
permutations are listed numerically or alphabetically, we call it
lexicographic order. The lexicographic permutations of 0, 1 and 2 are:

012   021   102   120   201   210

What is the millionth lexicographic permutation of the digits 0, 1, 2,
3, 4, 5, 6, 7, 8 and 9?

-}

lexI :: Char -> String -> Int
lexI c s = maybe 1 (id) $ elemIndex c s

lexOrder :: [Char] -> [[Char]]
lexOrder s
 | length s == 1    = [s]
 | length s == 2    = z : [reverse z]
 | otherwise        = concat $ map (\n -> h n) [0..((length s) - 1)]
                    where z = sort $ nub s -- why is the nub ignored here?
                          h :: Int -> [String]
                          h n = map (z!!n :) $ lexOrder $ filter (\c -> lexI c z /= n) z

p24 = (lexOrder "1234567890")!!999999

main :: IO()
main = 
    do
       putStrLn $ show $ p24