An Immigration officer handles transit visa exemption procedures for overseas tourists at the immigration area of Beijing Capital International Airport in Beijing, capital of China, Jan. 28, 2025.

给定两个数组，编写一个函数来计算它们的交集。 输出结果中每个元素出现的次数，应与元素在两个数组中出现的次数一致。 我们可以不考虑输出结果的顺序。 进阶: 如果给定的数组已经排好序呢？你将如何优化你的算法？ 如果 nums1 的大小比 nums2 小很多 ...

Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once. Find all the elements that appear twice in this array.