Here is a first shot, I get perl to allocate me a zero filled string of the correct size. calculate a chance step based on number of numbers left to find. Pick a random number then decrement this in countstep increments each time if find an unset bit in my string. once this is < 0 I look for the next unset bit (if I am not on one), set the bit and return its index.

I can think of a couple of optimisations, moving the endpoints would be a help. for the early numbers I may partiton the space and dive into about the right subblock searching from there although this does risk reducing the randomness... 

#!/usr/local/bin/perl
use strict;

my $number=1000;
my $string;
vec $string, $number, 1;

while ($number) {
    my $chance_step = 1/$number;
    my $rand=rand;
    my $i=0;
    while ($rand > 0) {
        if (vec $string, $i++, 1) {
            next
        } else {
            $rand-=$chance_step
        }
    }
    while (vec $string, $i, 1){$i++}
    vec($string, $i, 1)=1;
    print "$i, ";
    $number--
}

[download]

Cheers,
R.

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

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