[Haskell-cafe] warning - Euler problem spoiler enclosed

[Barbara Shirtcliff]

Ah, thanks!


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

> On 4 May 2011 13:13, Barbara Shirtcliff <barcs at gmx.com> 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 at gmail.com
> IvanMiljenovic.wordpress.com