Xref: utzoo comp.sources.wanted:7425 alt.msdos.programmer:47
Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!iuvax!watmath!watcgl!megauthier
From: megauthier@watcgl.waterloo.edu (Marc E. Gauthier)
Newsgroups: comp.sources.wanted,alt.msdos.programmer
Subject: Re: Need algorithm to scramble order of array
Message-ID: <9763@watcgl.waterloo.edu>
Date: 17 May 89 21:21:52 GMT
References: <3008@cps3xx.UUCP>
Reply-To: megauthier@watcgl.waterloo.edu (Marc E. Gauthier)
Organization: U. of Waterloo, Ontario
Lines: 27

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 [...]

Here's a simple way to do it in C:


	Object t, a[SIZE];
	int i, j;

	/*  this works by filling (backwards) the array with elements
	 *   picked randomly from the remaining ones at start of array
	 */
	for (i=SIZE-1; i>0; i--) {
	    j = random() % i;		/* return indice between 0 and i-1 */
	    t = a[i];
	    a[i] = a[j];
	    a[j] = t;
	}


Hope it helps.  It's a simple solution I always use to shuffle cards, etc.

Marc
-- 
Marc E. Gauthier   megauthier@watcgl.waterloo.edu   University of Waterloo