gistfile1.rb

class Chromosome
  ...
  def self.get_mates(chrs)
    i = 0
    res = {}

    #again, the counting is very important (and mistakes are very hard to catch)
    #so, we are writing it out in full
    while i < chrs.length
      res[i] = i+1
      res[i+1] = i

      i += 2
    end

  end
  ...
end