<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 {
    set<vector<int>> ans;
    void solve(vector<int>& a, vector<int>& temp, vector<bool>& idx, int n) {
        if (temp.size() == n) {
            ans.emplace(temp);
            return;
        }
        for (int i = 0; i < n; i++) {
            if (!idx[i]) {
                idx[i] = true;
                temp.push_back(a[i]);
                solve(a, temp, idx, n);
                idx[i] = false;
                temp.pop_back();
            }
        }
    }
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        int n = nums.size();
        vector<bool> idx(n, false);
        vector<int> temp;
        solve(nums, temp, idx, n);
        vector<vector<int>> vec(ans.size());
        copy(ans.begin(), ans.end(), vec.begin());
        return vec;
    }
};
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