Question

我正在尝试编写一个Array扩展名来执行以下操作：

我称之为：

%w[eggs bacon sausage].with_every_possibiity_of_multiples(2)

它给了我这些：

  [   
    %w[eggs, bacon, sausage],
    %w[eggs, eggs, bacon, sausage],
    %w[eggs, bacon, bacon, sausage],
    %w[eggs, bacon, sausage, sausage],
    %w[eggs, eggs, bacon, bacon, sausage],
    %w[eggs, eggs, bacon, bacon, sausage, sausage],
  ]

希望很清楚这里发生了什么。如果我用3而不是2的参数调用它，我会得到一个包含9个元素的数组，其中一个是%w[eggs, eggs, eggs, bacon, sausage]。

我正在努力想出如何写这篇文章。有什么建议吗？

Answer 1

正如@sawa指出的那样，你可能会把你的结果搞得一团糟。我猜测传球2可以获得8个元素，而不是6个，传球3可以获得27个而不是9个。

您可以充分利用Array#repeated_combination来生成重复每个元素的次数：

class Array
  def with_every_possibility_of_multiples(n)
    (1..n).to_a.repeated_permutation(size).map do |repeats|
      zip(repeats).flat_map{|elem, nb| [elem] * nb}
    end
  end
end

food = %w[eggs bacon sausage]
food.with_every_possibility_of_multiples(2) # =>
[["eggs", "bacon", "sausage"], ["eggs", "bacon", "sausage", "sausage"], ["eggs", "bacon", "bacon", "sausage"],
 ["eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage", "sausage"]]

food.with_every_possibility_of_multiples(3) # =>
[["eggs", "bacon", "sausage"],
 ["eggs", "bacon", "sausage", "sausage"],
 ["eggs", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "sausage"],
 ["eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "bacon", "sausage"],
 ["eggs", "bacon", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "bacon", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "sausage", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "bacon", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage"],
 ["eggs", "eggs", "eggs", "bacon", "bacon", "bacon", "sausage", "sausage", "sausage"]]

请注意repeated_permutation是Ruby 1.9.2的新功能。您可以在早期版本中使用require 'backports'，或使用product使用uglier版本：

# ...
(1..n).to_a.product(*[(1..n).to_a] * (size-1)).map do |repeats|
# ...

Answer 2

您可以尝试这种内置排列方法：

   %w[eggs bacon sausage].permutation(2).to_a

数组的排列，其中元素重复一定次数

2 个答案: