<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 len(nums) == 1:
            return [[nums[0]]]
        freq = collections.Counter(nums)
        n = len(nums)

        ret = []
        def dfs(cur: List[int]) -> List[List[int]]:
            if len(cur) == n:
                ret.append(cur.copy())
                return

            for num, f in freq.items():
                if not f:
                    continue
                freq[num] -= 1
                cur.append(num)
                dfs(cur)
                freq[num] += 1
                cur.pop()
            return ret

        return dfs(deque())
18400