<p>Given an integer array <code>nums</code> of <strong>unique</strong> elements, 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 = [1,2,3]
<strong>Output:</strong> [[],[1],[2],[1,2],[3],[1,3],[2,3],[1,2,3]]
</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>
	<li>All the numbers of&nbsp;<code>nums</code> are <strong>unique</strong>.</li>
</ul>

class Solution {
private:
    void helper(vector<vector<int>>& result,
                const vector<int>& nums,
                vector<int> current,
                unordered_set<int> visited,
                int index) {
        for (int i = index; i < nums.size(); ++i) {
            int num = nums[i];
            if (!visited.contains(num)) {
                visited.insert(num);

                current.push_back(num);
                result.push_back(current);

                helper(result, nums, current, visited, index + 1);

                current.pop_back();
            }
        }
    }

public:
    vector<vector<int>> subsets(const vector<int>& nums) {
        vector<vector<int>> result;
        unordered_set<int> visited;

        result.push_back({});
        helper(result, nums, {}, visited, 0);

        return result;
    }
};

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