Add method to check if a value is valid based on Luhn Algorithm

Author: Kimmie

lib/luhn_algorithm.rb

@@ -1,6 +1,15 @@
 require 'luhn_algorithm/version'
 
 module LuhnAlgorithm
- class Error < StandardError; end
- # Your code goes here...
+ NUMBER_ONLY = /^\d+$/
+
+ def self.valid?(value)
+ value = value.to_s.reverse
+ return false unless value.match(NUMBER_ONLY)
+ arr = value.chars.map(&:to_i)
+ (1...(arr.length)).step(2) do |index|
+ arr[index] = (arr[index] * 2).divmod(10).sum
+ end
+ (arr.sum % 10).zero?
+ end
 end

spec/luhn_algorithm_spec.rb

@@ -3,7 +3,54 @@
  expect(LuhnAlgorithm::VERSION).not_to be nil
  end
 
- it "does something useful" do
- expect(false).to eq(true)
+ [
+ {
+ value: '6011111111111117',
+ result: true
+ },
+ {
+ value: '6011111111111118',
+ result: false
+ },
+ {
+ value: 4222222222222,
+ result: true
+ },
+ {
+ value: '4222221222222',
+ result: false
+ },
+ {
+ value: '4522222222222',
+ result: false
+ },
+ {
+ value: '4522222222222',
+ result: false
+ },
+ {
+ value: '45222222222220',
+ result: false
+ },
+ {
+ value: '45222222222220',
+ result: false
+ },
+ {
+ value: '4111111111111111',
+ result: true
+ },
+ {
+ value: 'A122333333333',
+ result: false
+ },
+ {
+ value: 6011000990139424,
+ result: true
+ }
+ ].each do |hs|
+ it "return #{hs[:result]} for value #{hs[:value]}" do
+ expect(LuhnAlgorithm.valid?(hs[:value])).to eq(hs[:result])
+ end
  end
 end