public class Solution
extends Object
442 - Find All Duplicates in an Array\.
Medium
Given an integer array `nums` of length `n` where all the integers of `nums` are in the range `[1, n]` and each integer appears **once** or **twice** , return _an array of all the integers that appears **twice**_.
You must write an algorithm that runs in `O(n) `time and uses only constant extra space.
**Example 1:**
**Input:** nums = [4,3,2,7,8,2,3,1]
**Output:** [2,3]
**Example 2:**
**Input:** nums = [1,1,2]
**Output:** [1]
**Example 3:**
**Input:** nums = [1]
**Output:** []
**Constraints:**
* `n == nums.length`
* 1 <= n <= 105
* `1 <= nums[i] <= n`
* Each element in `nums` appears **once** or **twice**.