I wonder... if your aim is to learn something, then why is your approach so much like most newbies' approaches to shuffling arrays? I mean, picking an item, and if it's already been picked, try again... Just see Google Groups for examples on the newsgroups. That just seems like a step backward to me...

Anyway, though you do take care to make sure every loop finds at least one item, you will not get a nice even distribution. Let me give an example.

Suppose that your $N is 20, and by some weird coincidence, the numbers 1 .. 10 have already been picked, and nothing else. For your next pick, the numbers 12 to 20 all have 1 chance in 21 of being picked. So do the numbers 0 and 11. But if the drawn number is between 1 and 10 (about 10 chances in 21, that is almost 50%), your system will promote it to either 0 or 11...

Net result: there's 12 chances in 21, that is over 50%, that the next number picked, will be either 0 or 11.

So yes, this way, you'll tend to get clustered results, instead of a nicely spread, speckled, outcome.

In reply to Re^3: Generating 0 .. N Randomly and Efficiently by bart
in thread Generating 0 .. N Randomly and Efficiently by Limbic~Region

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