<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:

    void solve(vector<vector<int>> & ans , vector <int> nums , int index) {
        
        //base case

        if (index >= nums.size()) {
            int countOccurrence = count(ans.begin() , ans.end() , nums);

            if (countOccurrence == 0 ) {
                ans.push_back(nums);
            }
            else {
                return ;
            }
            
        }

        for (int j = index ; j<nums.size() ; j++) {
            swap(nums[index] , nums[j]);

            solve(ans , nums , index +1 );

            //backtrack
            swap (nums[index] , nums[j]);
        }
    }



public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {

        vector<vector<int>> ans;

        int index = 0;

        solve(ans , nums , index);

        return ans;
        
    }
};
38484