This was harder than I expected, I have been plagued by off by one errors and infinite loops but here is a version with a couple of optimations

It starts out nice and fast but bogs down for big sets looking for those last few unused values and I must admit it is pig ugly code. I think overall Limbic~Region's way of doing it is preferable.

#!/usr/local/bin/perl
use strict;
use integer;
$!++;

my $number=10000;
my $num_per_block=10;
my $string;
my $start=0;
my $end=$number-1;
vec $string, $end, 1;

while ($number) {
    my $block_size=(($end-$start+1)/$number)*$num_per_block;
    my $rand=int rand($number+1);
    my $found=1; # optimist
    my $guess_block=int($rand / $block_size);
    my $i=$start+($guess_block*$block_size);
    my $fiddled_rand=$rand-($guess_block*$num_per_block);
    while ($fiddled_rand > -1) {
        if (vec $string, $i, 1) {
            if ($i==$end+1) {
                # we ran off the end without getting a good number
                $found=0;
                last;
            }
        }else{
            $fiddled_rand--;
        }
        $i++;
    }

    unless ($found) {
        $i=$start;
        while ($rand) {
            unless (vec $string, $i++, 1) {
                $rand--;
            }
        }
    }
    print "$i+";
    vec($string, ($i-1), 1)=1;
    while (vec $string, $start, 1){$start++}
    while (vec $string, $end, 1){$end--}
    $number--;
}

[download]

I have another cunning plan to prevent that horrible slowdown near the end but it is at the cost of more memory (step 1 is thrown this abomination away ;)

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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