# File lib/text/white_similarity.rb, line 36
    def similarity(str1, str2)
      pairs1 = word_letter_pairs(str1)
      pairs2 = word_letter_pairs(str2).dup

      union = pairs1.length + pairs2.length

      intersection = 0
      pairs1.each do |pair1|
        if index = pairs2.index(pair1)
          intersection += 1
          pairs2.delete_at(index)
        end
      end

      (2.0 * intersection) / union
    end