Re: not enough real programmers?

[Brian.dot.Inglis@SystematicSw.ab.ca (Brian Inglis)]

On 9 Aug 1999 10:36:31 GMT, don@news.daedalus.co.nz (Don Stokes)
wrote:
>Everett M. Greene <mojaveg@ridgecrest.ca.us> wrote:
>>> 4.  "Write a program to perform a "perfect shuffle" on an array of 52
>>> numbers." 
>>Anybody with a good answer to question 4 doesn't need to be interviewing
>>for a job.  There are any number of companies, academic institutions,
>>etc. who would like a definitive answer to that problem.
>Huh?  Assuming "perfect" means "within the parameters of he system's
>random() function", 
>	void
>	shuffle(int array[52]) {
>		int tmparray[52], done[52];
>		int i,j;
>		for(i = 0; i < 52; i++) {
>			tmparray[i] = array[i];
>			done[i] = 0;
>		}
>		for(i = 0; i < 52; i++) {
>			for(j = random() % 52; done[j];) 
>				if(++j == 52) j = 0;
>			array[j] = tmparray[i];
>			done[j] = 1;
>		}
>	}
>works for me.  (It's much shorter if the routine is allowed to pick its
>own values -- if I know the values are 1..52, I can use the target array
>as my "done" array, and I don't need the temp array.  That's what I get
>after five minutes of codiong, anyway.)
>(do I get the job?)
>-- don
Try:
/* shuffle n items -- swap end items with random selection */
/* for n items from end to start while more than one left */
for (lastp = data + n - 1, items = n; 
				items > 1; 
					--lastp, --items)
{
/* select random item from those remaining */
	selectp		= data + rand() % items;
/* swap selected item with last item */
	temp		= *selectp;
	*selectp	= *lastp;
	*lastp		= temp;
}

Thanks. Take care, Brian Inglis 	Calgary, Alberta, Canada
-- 
Brian_Inglis@CSi.com 	(Brian dot Inglis at SystematicSw dot ab dot ca)
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