If you want to keep the order and edit in place, try this:

sub util_remove_duplicates{
  my $ref=shift;
  my %hash;
  @$ref=grep{!$hash{$_}++} @$ref;
}
my @array=qw(a b c a j k l m o p q k);
print "@array\n";
util_remove_duplicates(\@array);
print "@array\n";
[download]

OUTPUT:

a b c a j k l m o p q k
a b c j k l m o p q
[download]