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foreach my $e (@array1, @array2) {
    $union{$e}++ && $intersect{$e}++
}

my @sets = (\@array1, \@array2, ...);
for my $i (0..$#sets) {
...
    compute_stuff($sets[$i], $sets[$j]);
  }
}

sub union_intersection {
  my ($set1, $set2) = @_;
...
  for my $e (@$set1, @$set2) { ... }
  ...
}