- 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).