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

• <code>1 <= n <= 10⁵</code>

• 1 <= nums[i] <= n

• Each element in nums appears once or twice.