gistfile1.rb

class Chromosome
  ...
  def cross(mate)
    cs = crossover_site = rand(@bitstring.length-1)+1
 
    mate.bitstring[cs..-1], @bitstring[cs..-1] = @bitstring[cs..-1], mate.bitstring[cs..-1]
  end

  def self.do_crossings(chrs, mates)
    i = 0
    completed = []

    #not very idiomatic, but, the i variable is important
    while i < chrs.length

      #due to the symmetric nature of the data structure we're using
      if completed.include? i
        i += 1
        next
      end 
   
      chrs[i].cross(chrs[mates[i]])

      completed.push(mates[i])
      i += 1
    end 
    return chrs

  end
  ...
end