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From: cook@cpsvax.cps.msu.edu (Tom Cook)
Newsgroups: comp.sources.wanted,alt.msdos.programmer
Subject: Re: Need algorithm to scramble order of array
Message-ID: <3016@cps3xx.UUCP>
Date: 17 May 89 19:46:34 GMT
References: <3008@cps3xx.UUCP>
Sender: usenet@cps3xx.UUCP
Reply-To: cook@cpsvax.UUCP (Tom Cook)
Organization: Michigan State University, Computer Science Department
Lines: 21

In article <3008@cps3xx.UUCP> reedp@frith.egr.msu.edu () writes:
>I need a fast algorithm to randomly rearrange the order of elements in
>an array.  Right now I am just using a random number generator to form 
>a list of numbers that directly determines the order of the array like this:
>
>	n = size of array

I usually use something like this:

	for i = n to 2 step -1 do
	  begin
	    x = random number between 1 and i
	    swap array[i] and array[x]
	  end

This loop will always execute exactly n-1 times.

>Paul Reed
>Internet: reedp@horus.cem.msu.edu               Bitnet:   reedp@MSUCEM

Tom Cook        cook@cpsvax.msu.edu