in reply to Fast, Efficient Union and Intersection on arrays

I note two things: you only want the number of elements in the intersection and union, not the actual intersection and union; and your method suggests that there are no duplicates in the sets. So you don't need to find the union, explicitly. It is just the total number in I + J, minus the intersection.
sub get_int_uni2 { my ($in, $jn) = @_; my %i; @i{@$in} = (); my $int = grep exists $i{$_}, @$jn; return ($int, @$in + @$jn - $int); }
Sadly, I don't see any real improvement in performance (thanks to BrowserUK for the benchmarkery).

Caution: Contents may have been coded under pressure.