<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 {
public:
    vector<vector<int>> result;
    int n;

    void printVec(vector<int> vec)
    {
        for (int i = 0; i < vec.size(); i++)
        {
            cout << vec[i]<<" ";
        }
        cout << endl;
    }


    void helper(vector<int> src, vector<int> dst, unordered_set<int> vSet)
    {
        if (dst.size() == n)
        {
            result.push_back(dst);
            return;
        }
        
        for (int i = 0; i < n; i++)
        {            
            if (vSet.find(i) != vSet.end())
            {
                continue;
            }

            if (i != 0 && src[i] == src[i-1] && (vSet.find(i - 1) == vSet.end()))
            {
                continue;
            }

            dst.push_back(src[i]);
            vSet.insert(i);
            helper(src, dst, vSet);
            vSet.erase(i);
            dst.pop_back();
        }
    }

    vector<vector<int>> permuteUnique(vector<int>& nums) {
        n = nums.size();
        vector<int> vTmp;
        unordered_set<int> vSet;

        sort(nums.begin(), nums.end());
        helper(nums, vTmp, vSet);

        return result;
    }
};
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