順序を保持した組み合わせ

arr_comb.rb

# -*- coding: utf-8 -*-
class Array
  def comb
    n = self.length - 1
    0.upto(n) do |head_n|
      head_n.upto(n) {|tail_n| yield self[head_n..tail_n] }
    end
  end
end