aaa.rb

class Hamming
  def self.compute(a, b)
    [a, b].min.size.times.count {
      |i| a[i] != b[i]
    }
  end
end

class Hamming
  def self.compute(a, b)
    # select the shorter strand
    c = [a, b].min
    length = c.size

    # length.times returns an iterator that will return 0, 1, 2, ...length -1
    # count takes each element of an array and runs the block,
    # keeping count of the nunmber of times the block returns true
    # so this returns the number of strand matches.
    length.times.count { |i|
      a[i] != b[i]
    }
  end
end