use strict;

my $hash = {
   AA => {
      AA => {},
      AB => {},
      AC => {
         AA => {
            AA => {},
         },
      },
   },
};

add($hash);
add($hash->{AB});
add($hash->{AB}->{AA});
print_me($hash);

add($hash);
add($hash->{AC}) for (0..5);
add($hash->{AC}->{AC});
print_me($hash);

remove($hash->{AC},'AC');
print_me($hash);

remove($hash,'AB');
print_me($hash);

sub add {
   my $ref = shift;
   my $new = (sort keys %$ref)[-1];
   if ($new) {
      $ref->{++$new} = {};
   }
   else {
      $ref->{'AA'} = {};
   }
}

sub remove {
   my $ref = shift;
   my $sec = shift;
   
   delete $ref->{$sec}; 
   for (sort keys %$ref) {

      # skip higher section
      next if ord(substr($_,1,1)) < ord(substr($sec,1,1));

      my $new = substr($_,0,1) . chr(ord(substr($_,1,1))-1);

      my %new = %{$ref->{$_}};
      $ref->{$new} = \%new;
      delete $ref->{$_};
   }
}

sub print_me {
   my $ref = shift;
   my $ind = shift || '';
   for (sort keys %$ref) {
      print "$ind$_\n";
      print_me($ref->{$_},$ind."\t") if ref $ref->{$_};
   }
}