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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Lotto simulation
Date: Sun, 15 Jun 2014 21:54:33 +0100
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Date: 2014-06-15T21:54:33+01:00
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montgrimpulo <aghte@hotlinemail.com> writes:

> A workaround would be to test in each round, if that number has
> already been selected.  However, the probability would not be the same
> as with a reduced set as the selection would be always from the full
> set.

This seems perfectly reasonable.

If you think of numbered balls like the UK lottery, and after each pick
replace the picked ball by one without a number.  By the time you get to
the last 2 numbered balls, each of them has a 50% chance of being the
one that's eventually picked, no matter how many times you discard
unnumbered balls. Depending on the RNG, of course.

Another possibility: create an array of {ball-number, random-float},
sort by the random-float component, choose the first N entries.