Given an array nums of n integers where nums[i] is in the range [1, n], return an array of all the integers in the range [1, n] that do not appear in nums.

  Example 1: Input: nums = [4,3,2,7,8,2,3,1] Output: [5,6] Example 2: Input: nums = [1,1] Output: [2]

  Constraints:

n == nums.length
1 <= n <= 10⁵
1 <= nums[i] <= n

  Follow up: Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.