[Haskell-cafe] Permutations

[Jake Mcarthur]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

On Nov 30, 2008, at 10:17 AM, Luke Palmer wrote:

> On Sun, Nov 30, 2008 at 9:06 AM, Jake Mcarthur <jake at pikewerks.com>  
> wrote:
>> -----BEGIN PGP SIGNED MESSAGE-----
>> Hash: SHA1
>>
>> On Nov 30, 2008, at 9:03 AM, Andrew Coppin wrote:
>>>
>>> OK, so here's something just for fun:
>>>
>>> Given a list of items, find all possible *unique* permutations of  
>>> that
>>> list. (E.g., the input list is explicitly _allowed_ to contain  
>>> duplicates.
>>> The output list should not contain any duplicate permutations.)
>>>
>>> I've found one simple way to do this, but I'm sure there are  
>>> multiple
>>> valid approaches. So let's see what people come up with. ;-)
>>
>> Seems a bit easy, I think.
>>
>>   Data.List.permutations . nub
>
> That is not what he meant.  Given:
>
>  [1,1,2,2]
>
> The results should be:
>
>  [1,1,2,2]
>  [1,2,2,1]
>  [2,2,1,1]
>  [1,2,1,2]
>  [2,1,2,1]
>  [2,1,1,2]
>
> Assuming I didn't miss any...

Oh, I see. Okay, I see why that would be an interesting exercise then.  
Thanks for clearing that up.

- - Jake
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.4.8 (Darwin)

iEYEARECAAYFAkkyvlkACgkQye5hVyvIUKmMcwCgwQVbIB2IIV4yuS004K+JtGpw
b2YAoI9PihnG/R7W9Kl4884tgwPwOrYb
=MfCa
-----END PGP SIGNATURE-----