my $desired_page_count = 10;
# Structure holding all the different page layouts. ('l' = Landscape, 'p' = Portrait)
my $pages = {
    ll   => '01',
    pp   => '02',
    lp   => '03',
    pl   => '04',
    lpp  => '05',
    pll  => '06',
    plp  => '07',
    lpl  => '08',
    lll  => '09',
    ppp  => '10',
    ppl  => '11',
    llp  => '12',
    ppll => '13',
    llpp => '14',
};

my $photos = "llppllpplpppllplpplpplpllplpll";
# Make a really long layout -- at much over 100, it tends to hang up
$photos .= substr 'lp', rand 2 for 1..100;
$desired_page_count = int( length($photos)/ 2.7 );

my $page_regex = join '|', keys %$pages;
my $regex = "($page_regex)";
$regex .= "(?!\\$_)($page_regex)" for 1..($desired_page_count - 1);
print "\$regex is $regex\n";
if (my @pages = $photos =~ /^$regex$/) {  # Added the anchors as per SmugX's reply
   print "$pages->{$_}\n" for @pages;
}
else {
   print "Could not come up with no-repeat layout in $desired_page_count pages\n";
}