def check_digits? num
odd = true
num.to_s.gsub(/\D/,'').reverse.split('').map(&:to_i).collect { |d|
d *= 2 if odd = !odd
d > 9 ? d - 9 : d
}.sum % 10 == 0
end



def valid_luhn?(num)
num = num.to_s.reverse.split(//).map { |d| d.to_i }
odd = false
num.inject(0) { |memo, i|
memo + ((odd = !odd) ? i : (i*2 > 9 ? i*2 - 9 : i*2))
} % 10 == 0
end


Another small point, but in all regexps in the ccTypeCheck() method, the lowercase “d”s should all really be “\d” (ie. the digit character class for Ruby regexps)

(I guess the ruby source code on this page gets mangled when it is rendered as HTML by the blogging software, or some such thing, and the backslashes removed in the process)

Seriously though, I tried to give this one a bit more of the Ruby sass…so far it matches the results of the original.

Of course, it is a judgement call which is easier to read and to follow.

I think my only real claim to an improvement is that now the core of the algorithm is normalized to accept an Enumerable of numeric values; slightly more reusable maybe someday in some context?

def luhnother(ccNumber)
  ccNumber = ccNumber.gsub(/D/,'').split(//).collect { |digit| digit.to_i }
  parity = ccNumber.length % 2

  sum = 0
  ccNumber.each_with_index do |digit,index|
    digit = digit * 2 if index%2==parity
    digit = digit - 9 if digit > 9
    sum = sum + digit
  end

  return (sum%10)==0
end