115.Find All Duplicates in an Array Description 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. Example Input: [4, 3, 2, 7, 8, 2, 3, 1] Output: [2, 3] From LeetCode