So my brain hurt, but 2 seconds after I posted, I had an idea...

@hash{@range} = (1) x @range;  #guess I don't need to replicate now.
delete @hash{@ports};
@open = sort {$a <=> $b} keys %hash; 
#seems to work
[download]

I'd guess so, but until I Benchmark I don't know if its more efficient, but at least I can read it easier. If there are better ways out there, please share.

Regards,
Kristina