(12) How to make a hash remember, the order put elements into it?

Solution :

Ordinarily Perl does not guarantee the order of items in a hash to be in any predictable order.
If this is important you can easily add a "keep-in-order" behavior to a particular hash by "tying"
that hash to the Tie::IxHash module. Of course you must first use the module, then, once you tie
your hash to this module, the module will automatically add the desired behavio

Solution :

Use the Tie::IxHash from CPAN.

use Tie::IxHash;

tie my %myhash, 'Tie::IxHash';