Rosetta Code

Luhn test of credit card numbers

Validate account numbers with the Luhn checksum.

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Sourcerosettacode/popular/luhn_test_of_credit_card_numbers.vibe
def digit_value(char: string) -> int
  digit = "0123456789".index(char)
  raise ArgumentError, "expected a decimal digit" if digit == nil
  digit
end

def luhn_valid?(number: string) -> bool
  number_chars = number.chars
  sum = 0
  offset = 0
  index = number.length - 1

  while index >= 0
    digit = digit_value(number_chars.fetch(index))

    if offset % 2 == 1
      digit = digit * 2
      if digit > 9
        digit = digit - 9
      end
    end

    sum = sum + digit
    offset = offset + 1
    index = index - 1
  end

  sum % 10 == 0
end

def run -> { sample_false: bool, sample_true: bool, visa_false: bool, visa_true: bool }
  {
    sample_true: luhn_valid?("49927398716"),
    sample_false: luhn_valid?("49927398717"),
    visa_true: luhn_valid?("4012888888881881"),
    visa_false: luhn_valid?("4012888888881882")
  }
end

Output

Click Run example to see the result.

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