324. Permutations II

Given a collection of numbers, nums, that might contain duplicates, return all possible unique permutations in any order.

Example:
Input: nums = [1,1,2]
Output: [[1,1,2], [1,2,1], [2,1,1]]

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]]

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