Given a collection of numbers nums that might contain duplicates, return all possible unique permutations in any order.
Example 1:
Input: nums = [1,1,2]
Output: [[1,1,2],[1,2,1],[2,1,1]]
Explanation: Although there are two 1s, only three unique permutations exist.
Example 2:
Input: nums = [1,2,3]
Output: [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
Explanation: All elements are distinct, so all 6 permutations are unique.
1 <= nums.length <= 8-10 <= nums[i] <= 10