ruby-on-rails – 笛卡尔积ruby

class CartesianProduct
include Enumerable
# your code here
end
#Examples of use
c = CartesianProduct.new([:a,:b],[4,5])
c.each { |elt| puts elt.inspect }
# [:a,4]
# [:a,5]
# [:b,4]
# [:b,5]
c = CartesianProduct.new([:a,[])
c.each { |elt| puts elt.inspect }
# (nothing printed since Cartesian product
# of anything with an empty collection is empty)

我是ruby的新手.我理解如何定义笛卡儿积的实例方法,但我对此毫无头绪.我应该如何构造类对象以满足要求.

解决方法

我不会使用一个类,但保持问题的结构,我写道：

class CartesianProduct
  include Enumerable

  def initialize(xs,ys)
    @xs = xs
    @ys = ys
  end

  def each
    return to_enum unless block_given?
    @xs.each do |x| 
      @ys.each { |y| yield [x,y] }
    end
  end
end

相反,如果懒惰很重要,我只需编写xs.product(ys)或构建我自己的Array#lazy_product(参见本ticket).