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class Solution {
public:
    vector<vector<int>> res;
    vector<int> path;
    int n;
    vector<vector<int>> subsets(vector<int>& nums) {
        n = nums.size();
        dfs(nums, 0);
        return res;
    }

    void dfs(vector<int>& nums, int u){     //位置u上的数选还是不选
        if(u == n){
            res.push_back(path);
            return;
        }

        path.push_back(nums[u]);
        dfs(nums, u + 1);    //考虑下一位
        path.pop_back();
        dfs(nums, u + 1);

    }
};