Given a number determine whether or not it is valid per the Luhn formula.

The Luhn algorithm is a simple checksum formula used to validate a variety of identification numbers, such as credit card numbers and Canadian Social Insurance Numbers.

The task is to check if a given string is valid.

Validating a Number

Strings of length 1 or less are not valid. Spaces are allowed in the input, but they should be stripped before checking. All other non-digit characters are disallowed.

Example 1: valid credit card number

4539 1488 0343 6467

The first step of the Luhn algorithm is to double every second digit, starting from the right. We will be doubling

4_3_ 1_8_ 0_4_ 6_6_

If doubling the number results in a number greater than 9 then subtract 9 from the product. The results of our doubling:

8569 2478 0383 3437

Then sum all of the digits:

8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80

If the sum is evenly divisible by 10, then the number is valid. This number is valid!

my idea was to do these steps

1)�� reverse the input.

2)���� use this to double every second�� digit and calculate the sum of all the numbers :����

checkNumber :=�� (collection reverse selectwith index: [:item :index | (index % 2 == 0) . IfTrue: [item *2]] )�� sumNumbers

3) check if its a valid�� number by doing this :
��

^ (checkNumber % 10 == 0)��

is this a good game plan or has it flaws or can I do it better ?

Regards,

Roelof