如何在数组中查找并返回重复值 [英] How to find and return a duplicate value in array

问题描述

arr 是字符串数组:

["hello", "world", "stack", "overflow", "hello", "again"]

检查 arr 是否有重复项的简单而优雅的方法是什么，如果有，返回其中一个(无论哪个)?

What would be an easy and elegant way to check if arr has duplicates, and if so, return one of them (no matter which)?

示例:

["A", "B", "C", "B", "A"]    # => "A" or "B"
["A", "B", "C"]              # => nil

推荐答案

a = ["A", "B", "C", "B", "A"]
a.detect{ |e| a.count(e) > 1 }

<小时>

我知道这不是很优雅的答案，但我喜欢它.这是漂亮的单行代码.除非您需要处理庞大的数据集，否则工作得非常好.

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I know this isn't very elegant answer, but I love it. It's beautiful one liner code. And works perfectly fine unless you need to process huge data set.

正在寻找更快的解决方案?给你！

Looking for faster solution? Here you go!

def find_one_using_hash_map(array)
  map = {}
  dup = nil
  array.each do |v|
    map[v] = (map[v] || 0 ) + 1

    if map[v] > 1
      dup = v
      break
    end
  end

  return dup
end

它是线性的，O(n)，但现在需要管理多行代码，需要测试用例等.

It's linear, O(n), but now needs to manage multiple lines-of-code, needs test cases, etc.

如果您需要更快的解决方案，不妨试试 C.

If you need an even faster solution, maybe try C instead.

这里是比较不同解决方案的要点:https://gist.github.com/naveed-ahmad/8f0b926ffccf5fbd206a1cc58ce9743e

And here is the gist comparing different solutions: https://gist.github.com/naveed-ahmad/8f0b926ffccf5fbd206a1cc58ce9743e

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