Compare Two Lists of Unique Items in Perl ( The Gregorian Join )

Let's say you wanted to compare two lists of unique items and see what's in list A and not B, what's in B and not A, and what's in both. Say for example you had a list of all the rpms installed on two different machines ( the output of the command rpm -qa). Well, I can't say if this is the best way or not, but this works, and I think it looks pretty cool.

my (%comp,@a_only,@b_only,@both,$pushref);
map $comp{$_} = 2, @a;
map $comp{$_}++, @b;
map {
$pushref = $comp{$_} == 3 ? \@both
: $comp{$_} == 2 ? \@a_only
: \@b_only;
push(@$pushref,$_);
} keys %comp;