Re: Array of random, non-repeating numbers
Re: Array of random, non-repeating numbers
- Subject: Re: Array of random, non-repeating numbers
- From: Rob Ross <email@hidden>
- Date: Thu, 13 Jul 2006 11:12:19 -0700
On Jul 13, 2006, at 9:39 AM, Michael Ash wrote:
On 7/13/06, Bobby B <email@hidden> wrote:
Hey guys,
I'm trying to write a way to generate a random array of X numbers,
and
the numbers need to be between 0 and X, and not be repeating (its for
generating a random playlist.)
Just generate the random playlist directly, don't bother with indexes.
Put the tracks into an array, then use the canonical shuffle algorithm
which, in pseudocode, is:
for i from 0 to array_length - 2
random_index = random in [i, array_length - 1]
swap array[i] with array[random_index]
I did a lot of research on this at one time, long ago...
Your method is *almost* the best way of doing this :)
You can find papers someplace if you search online that show to
maximize "randomness" it is sufficient (and necessary) to only loop
over the first half of the array.
Statistically speaking, the shuffle is "more" random if you only loop
for i from 0 to array_length / 2
than if you loop over the entire array, and it takes half the time of
the full loop as well.
Rob Ross, Lead Software Engineer
E! Networks
email@hidden
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