<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 generatePerms(vector<int>& nums, int start, int end) {

        if (start == end) {
            std::string perm;

            for (auto el : nums) {
                if (el < 0) {
                    perm += '-';
                    el *= -1;
                }

                if (el > 9) {
                    perm += '1';
                    el %= 10;
                }

                perm += el + '0';
                perm += ',';
            }

            if (_s.find(perm) == _s.end()) {
                _perms.push_back(nums);
                _s.insert(perm);  
            }  
        }

        for (int i = start; i <= end; i++) {
            std::swap(nums[start], nums[i]);
            generatePerms(nums, start + 1, end);
            std::swap(nums[start], nums[i]);
        }
    }

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

        std::sort(nums.begin(), nums.end());

        generatePerms(nums, 0, nums.size() - 1);

        return _perms;
    }

private:
    std::unordered_set<std::string> _s;
    std::vector<std::vector<int>> _perms;
};
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