<p>Given an integer array <code>nums</code> that may contain duplicates, return <em>all possible</em> <span data-keyword="subset"><em>subsets</em></span><em> (the power set)</em>.</p>

<p>The solution set <strong>must not</strong> contain duplicate subsets. Return the solution in <strong>any order</strong>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> nums = [1,2,2]
<strong>Output:</strong> [[],[1],[1,2],[1,2,2],[2],[2,2]]
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> nums = [0]
<strong>Output:</strong> [[],[0]]
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10</code></li>
	<li><code>-10 &lt;= nums[i] &lt;= 10</code></li>
</ul>

class Solution {
public:
    vector<int> ss;
    set<vector<int>> st;

    void rec(vector<int>& nums, int k) {
        if (k == nums.size()) {
            st.insert(ss);
        }
        else {
            rec(nums, k+1);
            ss[nums[k] + 10]++;
            rec(nums, k+1);
            ss[nums[k] + 10]--;
        }
    }

    vector<vector<int>> subsetsWithDup(vector<int>& nums) {
        ss.assign(21, 0);
        rec(nums, 0);
        vector<vector<int>> ret;
        for (auto s : st) {
            vector<int> v;
            for (int i=0; i < 21; i++) {
                for (int j=0; j < s[i]; j++) {
                    v.push_back(i - 10);
                }
            }
            ret.push_back(v);
        }
        return ret;
    }
};
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