# time = O(N)   memory = O(N*M)

my $count = map @$_, values %h;

##</code><code>##

# time = O(N)   memory = O(N)

my $count = sum map { scalar @$_ } values %h;

##</code><code>##

# time = O(N)   memory = O(N)

my $count = 0;
$count += @$_ for values %h;

##</code><code>##

# time = O(N)   memory = O(1)

my $count = 0;
while (my ($k, $v) = each(%h)) {
   $count += @$v;
}