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itspriddle/gist:95462

Created April 14, 2009 22:10
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gistfile1.rb
def valid_card?(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
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