luhn.rb

module Luhn
  def self.is_valid?(number)
    
    array = number.to_s.chars.map(&:to_i)
    array2 = []

    array.reverse.each_with_index do |digit,digit_index|
      if digit_index % 2 == 1
        digit = digit * 2
        if digit >= 10
          digit = digit - 9
        end
      end
      array2 << digit
    end

    sum = array2.inject(0){ |total,x| total + x }

    return true if sum % 10 == 0
    return false if sum % 10 != 0
  end
end

# Test Numbers:
# 4194560385008504/5
# 377681478627336/7