Refactored ruby implementation of credit problem.

credit_refactor.rb

def credit_card_check() #main ruby method
  credit_card_no = 0
  until [13,14,15,16].include? credit_card_no.to_s.size #get credit card number
    puts "Number: "
    credit_card_no = gets.chomp
  end

  cardValid = checkCredit(credit_card_no)
  if cardValid == false
    puts "INVALID"
  else
    credit_key = {"5" => "MASTERCARD", "4" => "VISA", "3" => "AMEX" }
    puts credit_key[credit_card_no.to_s[0]]
  end
end

def checkCredit(card_no) #helper_method that implements checksum
  evenSum = 0
  oddSum = 0
  card_no.to_s.reverse.split("").each_with_index do |digit, idx|
    if idx == 0 || idx % 2 == 0
      evenSum += digit.to_i
    else
      double = digit.to_i * 2
      oddSum += double > 10? (double % 10) + 1 : double # use ternary operator as stand in for sumDigits
    end
  end
  (oddSum + evenSum) % 10 == 0 ? true : false
end