<p>Given a collection of numbers, <code>nums</code>,&nbsp;that might contain duplicates, return <em>all possible unique permutations <strong>in any order</strong>.</em></p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,1,2]
<strong>Output:</strong>
[[1,1,2],
 [1,2,1],
 [2,1,1]]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,2,3]
<strong>Output:</strong> [[1,2,3],[1,3,2],[2,1,3],[2,3,1],[3,1,2],[3,2,1]]
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 8</code></li>
	<li><code>-10 &lt;= nums[i] &lt;= 10</code></li>
</ul>

class Solution:
    def permuteUnique(self, nums: List[int]) -> List[List[int]]:
        if not nums:
            return []
        res = []
        cur = []
        index = 0
        def dfs(index):
            seen = set()
            if index == len(nums):
                res.append(list(nums))
            for i in range(index, len(nums)):
                if nums[i] not in seen:
                    seen.add(nums[i])
                    nums[i], nums[index] = nums[index], nums[i]
                    dfs(index + 1)
                    nums[i], nums[index] = nums[index], nums[i]
        dfs(0)
        return res


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