如何找到在一个数组中重复的元素？

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让我们说我有n个元素（数字或单词）的阵列，我想找到所有发生的比数组中多次的元素。什么是在性能方面这样做的最有效的方法？

Let's say I have an array of n elements(numbers or words), I want to find all the elements which occur more than once in the array. What is the most efficient approach of doing this in terms of performance?

PS：我可以在阵列第一排序，但只有当没有太大影响的总性能。此外，虽然这主要是PHP的，我想知道一个算法或逻辑可以在其他平台上实现了。

PS: I can sort the array first, but only if that doesn't affect the total performance much. Also, though this is mainly php, i would like to know a algorithm or logic that can be implemented on other platforms too.

推荐答案

您可以使用的 array_count_values​​ 和 array_filter

$array = array(1, "hello", 1, "world", "hello"); $new=array_filter(array_count_values($array),'custom_filter'); print_r($new); function custom_filter($val) { return $val > 1; }

输出

Array ( [1] => 2 [hello] => 2 )