# [plt-scheme] Re: User data structures and equality

On 4/10/07, Paulo J. Matos <pocm at soton.ac.uk> wrote:
>* Hello all,
*>*
*>* I want to define a bijective function f: D -> N, where D is a finite
*>* collection of user data structures which have a known equality
*>* procedure that given two elements of D know if they are equal or not.
*>* Implementing this with alists is trivial, however, computing f and
*>* f^-1 is done in linear time. The 'good' way would be hash-tables but I
*>* can't since I have no hash-function for the data structures, only the
*>* equality procedure [there is no obvious ordering between the user
*>* structures since I don't really know what they are].
*>*
*
Agrh, I always forget something... Another way (better) would be to
use a simple vector. Computing f^-1 is constant, f is linear but I'm
still hoping for a better solution.
>* Any suggestions?
*>*
*>* Cheers,
*>* --
*>* Paulo Jorge Matos - pocm at soton.ac.uk
*>* http://www.personal.soton.ac.uk/pocm
*>* PhD Student @ ECS
*>* University of Southampton, UK
*>*
*
--
Paulo Jorge Matos - pocm at soton.ac.uk
http://www.personal.soton.ac.uk/pocm
PhD Student @ ECS
University of Southampton, UK