use File::Find;
my @dupes;
{
    my %dirnames;
    sub dupe_dir {
        -d or return;
        if (exists $dirnames{$_}) {
            push @dupes, $File::Find::name;
        }
        else {
            ++$dirnames{$_}
        }
        1;
    }
}

find(\&dupe_dir)
print $_, $/ for @dupes;