题目：

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代码(首刷看解析 2024年2月3日）：

class Solution {
private:
    vector<vector<int>> res;
    vector<int> path;
public:
    void backtracking(vector<int>& nums, int startIndex) {
        res.push_back(path);
        for (int i = startIndex; i < nums.size(); ++i) {
            path.push_back(nums[i]);
            backtracking(nums, i + 1);
            path.pop_back();
        }
    }
    vector<vector<int>> subsets(vector<int>& nums) {
        backtracking(nums, 0);
        return res;
    }
};