vector<vector<int>> subsets(vector<int>& nums) {

// sort

sort(nums.begin(), nums.end());

vector<vector<int>> res;

vector<int> subsets;

dfs(nums, 0, subsets, res);

return res;

}

void dfs(vector<int>& nums, int k, vector<int>& subsets, vector<vector<int>>& res) {

// Save the current subsets to res

res.push_back(subsets);

// add a new element to the subset

for(int i = k; i < nums.size(); i++) {

subsets.push_back(nums[i]);

// next layer search

dfs(nums, i+1, subsets, res);

// backtrack

subsets.pop_back();

}

}