README.md (1738B) - raw
1 # Luhn 2 3 Welcome to Luhn on Exercism's Perl 5 Track. 4 If you need help running the tests or submitting your code, check out `HELP.md`. 5 6 ## Instructions 7 8 Given a number determine whether or not it is valid per the Luhn formula. 9 10 The [Luhn algorithm](https://en.wikipedia.org/wiki/Luhn_algorithm) is 11 a simple checksum formula used to validate a variety of identification 12 numbers, such as credit card numbers and Canadian Social Insurance 13 Numbers. 14 15 The task is to check if a given string is valid. 16 17 ## Validating a Number 18 19 Strings of length 1 or less are not valid. Spaces are allowed in the input, 20 but they should be stripped before checking. All other non-digit characters 21 are disallowed. 22 23 ### Example 1: valid credit card number 24 25 ```text 26 4539 3195 0343 6467 27 ``` 28 29 The first step of the Luhn algorithm is to double every second digit, 30 starting from the right. We will be doubling 31 32 ```text 33 4_3_ 3_9_ 0_4_ 6_6_ 34 ``` 35 36 If doubling the number results in a number greater than 9 then subtract 9 37 from the product. The results of our doubling: 38 39 ```text 40 8569 6195 0383 3437 41 ``` 42 43 Then sum all of the digits: 44 45 ```text 46 8+5+6+9+6+1+9+5+0+3+8+3+3+4+3+7 = 80 47 ``` 48 49 If the sum is evenly divisible by 10, then the number is valid. This number is valid! 50 51 ### Example 2: invalid credit card number 52 53 ```text 54 8273 1232 7352 0569 55 ``` 56 57 Double the second digits, starting from the right 58 59 ```text 60 7253 2262 5312 0539 61 ``` 62 63 Sum the digits 64 65 ```text 66 7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57 67 ``` 68 69 57 is not evenly divisible by 10, so this number is not valid. 70 71 ## Source 72 73 ### Created by 74 75 - @bistik 76 77 ### Contributed to by 78 79 - @alexkalderimis 80 - @kytrinyx 81 - @m-dango 82 - @pgraemer 83 - @rfilipo 84 85 ### Based on 86 87 The Luhn Algorithm on Wikipedia - http://en.wikipedia.org/wiki/Luhn_algorithm