Here's a solution from the Perl Cookbook which gets the union, intersection, and symmetric difference.

my @a = (2,4,6,8,10);
my @b = (1,2,3,4,5);

my @isect = my @diff = my @union = ();
my %count;

$count{$_}++ for (@a, @b);

@union = keys %count;

for (keys %count) {
    push @{$count{$_} == 2 ? \@isect : \@diff}, $_;
}
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