<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>> helper(vector<int> v) {
        if(v.size()==0) return {};
        if(v.size()==1) return {{v[0]}};
        vector<vector<int>> res;
        unordered_set<int> s;
        for(int i=0;i<v.size();i++) {
            if(s.find(v[i])==s.end()){
                s.insert(v[i]);
                vector<int> t = v;
                t.erase(t.begin()+i);
                vector<vector<int>> tres = helper(t);
                for(int j=0;j<tres.size();j++) {
                    tres[j].push_back(v[i]);
                    res.push_back(tres[j]);
                }
            }
        }
        return res;
    } 
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        vector<vector<int>> res = helper(nums);
        // for(int i=0;i<res.size();i++) {
        //     reverse(res[i].begin(), res[i].end());
        // }
        return res;
    }
};
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