if (-f $_) {
    if (-s _ == 0) {
      print $File::Find::name, "\n";
    }
  }

##</code><code>##

my %usage;

sub wanted {
  if (-f $_) {
    my $size = -s _;
    $usage{$File::Find::dir} += $size;
    if ($size == 0) {
      print $File::Find::name, "\n";
    }
  }
}

sub postprocess {
  print "Usage of $File::Find::dir is $usage{$File::Find::dir}\n";
}

find({wanted => \&wanted, postprocess => \&postprocess}, ...);