my ($i, %seen) = (0);

my @no_dup =
    grep { 2 < push @{$seen{/(pattern)/}}, $i++ }
    @with_dup;

@no_dup = map { 2 < @$_ ? $no_dup[$_->[0]] : () } values %seen;

##</code><code>##

my ($i, %seen) = (0);

my @no_dup =
    grep { -1 != ($seen{/(pattern)/} = exists $seen{$1} ? -1 : $i++) }
    @with_dup;

@no_dup = @no_dup{grep $_ != -1, values %seen};