<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 generatePermute(vector<int>&nums,vector<vector<int>>&ans,int start){
        //base case
        if(start==nums.size()){
            ans.push_back(nums);
            return;
        }
        unordered_map<int,bool>visited;
        for(int i=start;i<nums.size();i++){
            if(visited.find(nums[i])!=visited.end()){
                continue;
            }
            visited[nums[i]]=true;
            swap(nums[i],nums[start]);
            generatePermute(nums,ans,start+1);
            //backtracking
            swap(nums[i],nums[start]);

        }
    }
    vector<vector<int>> permuteUnique(vector<int>& nums) {
         vector<vector<int>>ans;
        generatePermute(nums,ans,0);
        //push ans into set
        set<vector<int>>st;
        for(auto it:ans){
            st.insert(it);         
        }
        ans.clear();
        for(auto it:st){
            ans.push_back(it);
        }
        return ans;
    }
};
16224