It looks like a cool problemfrom where did you take it?
I hope I can discuss my approch to this problem :
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.
I like people that are always thinking in string as if a collection of number would not make it :)
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 6467The 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 3437Then sum all of the digits:
8+5+6+9+2+4+7+8+0+3+8+3+3+4+3+7 = 80If 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
you can also��
1 to: xx by: 2 do:��
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
--------------------------------------------St��phane Ducasse03 59 35 87 52Assistant: Julie Jonas��FAX 03 59 57 78 50TEL 03 59 35 86 16S. Ducasse - Inria40, avenue Halley,��Parc Scientifique de la Haute Borne, B��t.A, Park PlazaVilleneuve d'Ascq 59650France