如何有效地提取 Ruby 数组中的重复元素? [英] How can I efficiently extract repeated elements in a Ruby array?

问题描述

我有一个像 [1,1,1,2,4,6,3,3] 这样的数组，我想获取重复元素的列表，在本例中为 [1,3].我是这样写的:

I have an array like [1,1,1,2,4,6,3,3] and I would like to get the list of repeated elements, in this case [1,3]. I wrote this:

my_array.select{|obj|my_array.count(obj)>1}.uniq

但它非常低效(o(n²)).你有更好的主意吗?如果可能的话，简洁.

But it is tragically inefficient (o(n²)). Do you have a better idea? If possible concise.

谢谢

推荐答案

灵感来自 Ilya Haykinson 的回答:

Inspired by Ilya Haykinson's answer:

def repeated(array)
  counts = Hash.new(0)
  array.each{|val|counts[val]+=1}
  counts.reject{|val,count|count==1}.keys
end

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