Subj : Re: combo numbering
To   : comp.programming
From : Thad Smith
Date : Thu Oct 06 2005 11:49 pm

bob@coolgroups.com wrote:

> If you have 52 cards and you choose 7, there are 133,784,560
> possibilities.
> 
> So, let's say you have 7 playing cards. Is there an easy way to convert
> these cards into a number between 0 and 133,784,559?

I wrote a set of C functions a while ago to convert from a combination 
index to the combination, and the reverse.  It has a lot more than you 
would need for this, but you are welcome to use it.

The added complexity comes from allowing sets with some identical items 
and setting a maximum of the number of identical items in a combination. 
  It also has code to detect arithmetic overflow in computing the index.

The header file describes the interface.  If you define TEST then the 
code will compile a test program to allow you to convert back and forth.

http://home.ionsky.com/~thadsmith/combx.ZIP

Thad

.