class DNA
  def initialize( str )
    @strand = str.chars
  end

  def hamming_distance( str )

    other_strand = str.chars
    distance = 0

    @strand.each_with_index do | letter, i |
      if other_strand[i]
        distance += 1 if letter != other_strand[i]
      end
    end

    distance
  end

end