agarie/measurable

module Measurable
  module Hamming

    # call-seq:
    #     hamming(s1, s2) -> Integer
    #
    # Count the number of different characters between strings +s1+ and +s2+,
    # that is, how many substitutions are necessary to change +s1+ into +s2+ and
    # vice-versa.
    #
    # See: http://en.wikipedia.org/wiki/Hamming_distance
    #
    # Arguments:
    # - +s1+ -> A String.
    # - +s2+ -> A String with the same size of +s1+.
    # Returns:
    # - The number of characters in which +s1+ and +s2+ differ.
    # Raises:
    # - +ArgumentError+ -> The sizes of +s1+ and +s2+ don't match.
    def hamming(s1, s2)
      # TODO: Change this to a more specific, custom-made exception.
      raise ArgumentError if s1.size != s2.size

      s1.chars.zip(s2.chars).reduce(0) do |acc, c|
        acc += 1 if c[0] != c[1]
        acc
      end
    end
  end

  extend Measurable::Hamming
end