如何在红宝石中组合/排列？

Question

我有这个熟悉的问题,看起来像数学世界的排列/组合.

如何通过ruby实现以下功能？

badges = "1-2-3"

badge_cascade = []
badges.split("-").each do |b|
  badge_cascade << b
end

Gives: => ["1", "2", "3"]

But I want it to be is:

=> ["1", "2", "3", 
  "1-2", "2-3", "3-1", "2-1", "3-2", "1-3", 
  "1-2-3", "2-3-1", "3-1-2"]

Answer 1

功能方法:

bs = "1-2-3".split("-")
strings = 1.upto(bs.size).flat_map do |n| 
  bs.permutation(n).map { |vs| vs.join("-") } 
end
#=> ["1", "2", "3", "1-2", "1-3", "2-1", "2-3", "3-1", "3-2", "1-2-3", "1-3-2", "2-1-3", "2-3-1", "3-1-2", "3-2-1"]

Answer 2

您需要使用Array#permutation方法来获取所有排列:

arr = "1-2-3".split '-' # => ["1", "2", "3"]
res = (1..arr.length).reduce([]) { |res, length|
  res += arr.permutation(length).to_a
}.map {|arr| arr.join('-')}

puts res.inspect
# => ["1", "2", "3", "1-2", "1-3", "2-1", "2-3", "3-1", "3-2", "1-2-3", "1-3-2", "2-1-3", "2-3-1", "3-1-2", "3-2-1"]

让我解释一下代码:

1. 您将字符串拆分为数组,将分隔符传递'-'给String#split方法

2. 您需要长度为1,2,3的所有排列.范围1..arr.length表示所有这些长度.

3. 您使用Enumerable #reduce收集所有排列的数组.您将在此处获得数组:

   [["1"], ["2"], ["3"], ["1", "2"], ["1", "3"], ["2", "1"], ["2", "3"], ["3", "1"], ["3", "2"], ["1", "2", "3"], ["1", "3", "2"], ["2", "1", "3"], ["2", "3", "1"], ["3", "1", "2"], ["3", "2", "1"]]
   

4. 您可以使用Array#join将此数组的所有子数组转换为字符串,并使用Enumerable #map中的'-'分隔符