Re: [Haskell-cafe] warning - Euler problem spoiler enclosed

Ah, thanks! On May 4, 2011, at 7:21 AM, Ivan Lazar Miljenovic wrote:

On 4 May 2011 13:13, Barbara Shirtcliff wrote:

...

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.

[snip]

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

As a guess, I think it's from the usage of length on the right-hand size.

Also, note that "lexOrder s@[_] = [s]" is nicer than "lexOrder s | length s == 1 = [s]".

-- Ivan Lazar Miljenovic Ivan.Miljenovic@gmail.com IvanMiljenovic.wordpress.com