summarize.rb

class Summarizer
  
  def initialize(text)
    @text = text
  end
  
  def summarize
    summary = []
    
    paragraphs = split_paragraphs
    ranks = get_ranks

    paragraphs.each do |p|
      sentence = best_sentence(p, ranks)
      summary << sentence if sentence
    end
    
    summary.join("\n")
  end
  
  private
  
  def split_paragraphs
    @text.split("\n\n")
  end
  
  def split_sentences(content = @text)
    content.gsub("\n", ". ").split(". ")
  end
  
  def intersect(sentence1, sentence2)
    split1 = sentence1.split(" ")
    split2 = sentence2.split(" ")
    
    return 0 if (split1.length + split2.length) == 0
        
    ((split1 & split2).length) / ((split1.length + split2.length) / 2).to_f
      
  end
  
  def format(sentence)
    sentence.gsub(/\W+/, '')
  end
  
  def get_ranks
    sentences = split_sentences
    sentences_length = sentences.length
    
    values = []
    sentences_length.times.each do |i|
      values << []
      sentences_length.times.each do |x|
        values[i] << 0
      end
    end
    
    sentences_length.times.each do |i|
      sentences_length.times.each do |x|
        values[i][x] = intersect(sentences[i], sentences[x])
      end
    end
            
    sentences_hash = {}
    
    sentences_length.times.each do |i|
      score = 0
      sentences_length.times.each do |x|
        next if i == x
        score += values[i][x]
      end
      sentences_hash[format(sentences[i])] = score
    end
    sentences_hash
  end
  
  def best_sentence(paragraph, sentences_hash)
    sentences = split_sentences(paragraph)
    return "" if sentences.length < 2
    
    best = ""
    max_value = 0
    
    sentences.each do |s|
      stripped = format(s)
      if stripped
        if sentences_hash[stripped] > max_value
          max_value = sentences_hash[stripped]
          best = s
        end
      end
    end
    
    best
  end
  
end

# USAGE

text = "Twitter's first-party Android app has been steadily getting better over the years, but it has generally maintained the same look and feel, with four navigation tabs located at the top of your timeline. That's going to change drastically in the near future however, as a completely redesigned version of the app is now available to those that have signed up for beta testing.\n\nThe app is listed as version 5.0, and completely ditches the old tabbed layout for a sliding panel menu. It's still possible to swipe between columns for Home, Notifications, Messages, and your profile, but instead of only four columns, the app now has seven. The three new columns are dedicated to Activity, Trending, and finding new people to follow on the service."
puts Summarize.new(text).summarize