<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<int> tmp;
    vector<vector<int>> ans;
    void fn( int i, vector<int>& nums){
        int n = nums.size();
        if( i == n){
            ans.push_back(nums);
            return;
        }

        unordered_set<int> st;
        for( int j=i; j<n; j++){
            if( st.count(nums[j]) == 1) continue;
             st.insert(nums[j]);
            if( i != j){
               
                swap(i,j,nums);
            }
            fn(i+1,nums);
            if( i != j){
                swap(i,j,nums);
            }
        }
    }   

    void swap(int i, int j, vector<int> & nums){
        int tmp = nums[j];
        nums[j]=nums[i];
        nums[i]=tmp;
    }

    vector<vector<int>> permuteUnique(vector<int>& nums) {
        tmp.clear();
        ans.clear();
        // sort(nums.begin(), nums.end());
        fn(0,nums);
        return ans;
    }
};
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