Luhn

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!

Example 2: invalid credit card number

8273 1232 7352 0569

Double the second digits, starting from the right

7253 2262 5312 0539

Sum the digits

7+2+5+3+2+2+6+2+5+3+1+2+0+5+3+9 = 57

57 is not evenly divisible by 10, so this number is not valid.

Source

The Luhn Algorithm on Wikipedia http://en.wikipedia.org/wiki/Luhn_algorithm

Version compatibility

This exercise has been tested on Julia versions >=1.0.

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

Your solution



In [ ]:

    
# submit

Test suite



In [ ]:

    
using Test

# include("luhn.jl")

@testset "invalid" begin
    @testset "single digit strings can not be valid" begin
        @test !luhn("1")
    end

    @testset "A single zero is invalid" begin
        @test !luhn("0")
    end

    @testset "invalid Canadian SIN" begin
        @test !luhn("046 454 287")
    end

    @testset "invalid credit card" begin
        @test !luhn("8273 1232 7352 0569")
    end

    @testset "valid strings with a non-digit added become invalid" begin
        @test !luhn("046a 454 286")
    end
end

@testset "valid" begin
    @testset "valid Canadian SIN" begin
        @test luhn("046 454 286")
    end
end

Prepare submission

To submit your exercise, you need to save your solution in a file called luhn.jl before using the CLI. You can either create it manually or use the following functions, which will automatically write every notebook cell that starts with # submit to the file luhn.jl.



In [ ]:

    
# using Pkg; Pkg.add("Exercism")
# using Exercism
# Exercism.create_submission("luhn")