78

class Solution {
public:
    void backtrack(vector<vector<int>> &ans, vector<int> &nums, int start, vector<int> &temp){
        ans.push_back(temp);
        for(int i=start;i<nums.size();i++){
            temp.push_back(nums[i]);
            backtrack(ans, nums, i+1, temp);
            temp.pop_back();
        }
    }
    vector<vector<int>> subsets(vector<int>& nums) {
        ios_base::sync_with_stdio(false);
        cin.tie(NULL);
        vector<vector<int>> ans;
        vector<int> temp;
        backtrack(ans, nums, 0, temp);
        return ans;
    }
};