If I grok what you mean

When Page 3 links to Page 7 you wish to ensure Page 7 also links back to Page 3...

Pass 1, examine all pages and build a hash keyed by linked page containing arrayrefs to an array of pages that linked it. for instance if on page 3 you found a link to page 7 push @{$hash{7}}, 3 of course you check first the key for 7 exists and create if required

Pass 2, go through the hash keys and see what is in the attached array to get a list of all pages that linked to this page

update

Oh how dumb I am, sequential integer page numbers and I am babbling on about a hash... replace the above code with push @{$array[7]}, 3 and s/hash/array/g

Here is a rough framework

# something like this....
# @Pages is a list of integer page numbers
# get_links_linked_from($) does what it looks like
foreach my $page (@Pages) {
    my @Links=&get_pages_linked_from($page);
    foreach (@Links) {
        $Link_Store[$_]=[] unless $Link_Store[$_];
        push @{$Link_Store[$_]}, $page;
    }
}
# assuming you start on page 1
for (my $i=1; $i<=$#Link_Store; $i++) {
    my $linkers = join ", ", @{$Link_Store[$i]};
    print "Page $i linked from $linkers\n"
}
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Cheers,
R.