<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:
    void permUnRec(vector<vector<int>>& ans, vector<int>& cur_ans, std::map<int,int>& elements, vector<int>& nums){
        if(cur_ans.size() == nums.size()){ans.push_back(cur_ans); return;}

        std::unordered_set<int> used;
        for(int a : nums){
            if(!used.contains(a) && elements[a] > 0){
                used.insert(a);
                elements[a]--;
                cur_ans.push_back(a);
                permUnRec(ans, cur_ans, elements, nums);
                elements[a]++;
                cur_ans.pop_back();
            }
        }
    }
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        std::map<int, int> elements;
        for(int i : nums){
            if(!elements.contains(i)){elements[i] = 1;}
            else{elements[i]++;}
        }
        vector<vector<int>> ans;
        vector<int> cur_ans;
        permUnRec(ans, cur_ans, elements, nums);
        return ans;
        
    }
};
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