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.