my @arr1 = (1, 2, 3, 4, 5);
my @arr2 = (4, 5, 6, 7, 8);

my @arr3 = f(\@arr1, \@arr2);

sub f {
#234567890#234567890#234567890
@h{map{@$_}@_}=1;keys%h
}