<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 {
private:
    vector<vector<int>> result;
    vector<int> path;
    void backtracking(vector<int>& nums,vector<bool> used){
        if(path.size()==nums.size()){
            result.push_back(path);
            return;
        }
        for(int i=0;i<nums.size();i++){
            if(i>0 && nums[i]==nums[i-1] && used[i-1]==false){
                continue;
            }
            if(used[i]==true) continue;
            if(used[i] == false){
                used[i]= true;
                path.push_back(nums[i]);
                backtracking(nums, used);
                path.pop_back();
                used[i]=false;
            }
        }
    }
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        result.clear();
        path.clear();
        vector<bool> used(nums.size(),false);
        sort(nums.begin(),nums.end());
        backtracking(nums, used);
        return result;
    }
};
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