This script ran in less than 1 second. But it doesn't print out the subarrays which would make it faster. Still, I can't see why it is taking your script over an hour to run. Unless you are repeatedly constructing a 90_000 element array and the other arrays and hash. 
#!/usr/bin/perl
use strict;
use warnings;

my @unique = map int rand(45000), 1 .. 90_000;
my %first_index = map { $unique[$_] => $_ }  reverse 0 .. $#unique;

my @in = map $unique[rand @unique], 1 .. 10000;

my @idxs = sort {$a <=> $b} map $first_index{$_} // (), @in;

my $first = $idxs[0];
my @sub_arrays;

my $time = time;

for (1 .. $#idxs)
{
    my $diff = $idxs[$_] - $first ;
    if (($diff > 5) && ($diff < 10)) 
    {
        push @sub_arrays,  [ @unique[$first+1..$idxs[$_]-1] ];
    }
    $first = $idxs[$_];
}

#use Data::Dumper; print Dumper \@sub_arrays;
print "Number of sub arrays: ", scalar @sub_arrays, "\n";
print "Time = ", time - $time, "\n";

[download]
This printed results for 1 run: 
Number of sub arrays: 1330
Time = 0

[download]

In reply to Re: Better way to do this by Cristoforo
in thread Better way to do this by PetreAdi

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.