<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 {
    vector<vector<int>> res;
    void backtrack (vector<int> &nums, vector<bool> vis, vector<int> cur={}) {
        if (cur.size() == nums.size()) {
            res.push_back(cur);
            return;
        }
        for (int i=0; i < nums.size(); i++) {
            if (vis[i] || (i > 0 && nums[i] == nums[i-1] && vis[i-1])) continue;
            vis[i] = true;
            cur.push_back(nums[i]);
            backtrack(nums, vis, cur);
            cur.pop_back();
            vis[i] = false;
        }
    }
public:
    vector<vector<int>> permuteUnique(vector<int>& nums) {
        vector<bool> vis(nums.size(), false);
        sort(nums.begin(), nums.end());
        backtrack(nums, vis);
        return res;
    }
};
21325