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.
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.length1 <= n <= 1051 <= nums[i] <= n- Each element in
numsappears once or twice.
Follow up: Could you do it without extra space and in O(n) runtime?