Groups > comp.games.development.programming.algorithms > #41

Re: Shuffling

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From	hexxial <hexxial@gmail.com>
Newsgroups	comp.games.development.programming.algorithms
Subject	Re: Shuffling
Date	Sun, 20 Jan 2013 22:58:00 +0000
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Em 30-07-2012 11:52, Mok-Kong Shen escreveu:
>
> For playing cards there are riffle shuffling etc. With computers
> one is not dependent on constraints resulting from manual working
> and consequently could specify more complex operations that may be
> rather inconvenient to be performed manually. I like thus to pose
> a general question as follows:
>
> Given a list of n different elements, could one find a shuffling
> (permutation) operation on them which can be characterized by the
> numerical value of one single parameter (corresponding essentially
> to the cutting point of a card deck into two parts in manual
> shuffling) and which is likely to lead to the highest degree of
> derangement (disorder) of the original list?
>
> I have done some small amount of experiments but I don't think
> to have yet found a really optimal permutation operation.
>
> Thanks in advance.
>
> M. K. Shen

Pokerstars is an online poker room. They offer a webpage explaining the 
shuffling algorithm they use:

"To perform an actual shuffle, we use another simple and reliable algorithm:
- first we draw a random card from the original deck (1 of 52) and place 
it in a new deck - now original deck contains 51 cards and the new deck 
contains 1 card
- then we draw another random card from the original deck (1 of 51) and 
place it on top of the new deck - now original deck contains 50 cards 
and the new deck contains 2 cards
- we repeat the process until all cards have moved from the original 
deck to the new deck
This algorithm does not suffer from "Bad Distribution Of Shuffles" 
described in [1]."

It's actually pretty simple and effective, given a good random number 
generator (they also explain how they generate numbers using entropy 
generated by the users). If you're interested check out their webpage 
explaining it: http://www.pokerstars.com/poker/room/features/security/

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Shuffling Mok-Kong Shen <mok-kong.shen@t-online.de> - 2012-07-30 12:52 +0200
  Re: Shuffling Mok-Kong Shen <mok-kong.shen@t-online.de> - 2012-08-01 20:14 +0200
  Re: Shuffling hexxial <hexxial@gmail.com> - 2013-01-20 22:58 +0000

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