[LeetCode] Subsets

vector<vector<int>> combine(vector<int> &nums, int k) {
	vector<vector<int>> combinations;
	if (k == 0)
	{
		vector<int> combination;
		combinations.push_back(combination);
		return combinations;
	}
	if (k == nums.size())
	{
		combinations.push_back(nums);
		return combinations;
	}
	vector<int> nums_tmp = nums;
	int comboNum = nums[0];
	nums_tmp.erase(nums_tmp.begin(), nums_tmp.begin()+1);
	vector<int> combination;
	combination.push_back(comboNum);
	vector<vector<int>> combinationsWithoutComboNum = combine(nums_tmp, k-1);
	for (int j = 0; j < combinationsWithoutComboNum.size(); j++)
	{
		vector<int> combination = combinationsWithoutComboNum[j];
		combination.insert(combination.begin(), comboNum);
		combinations.push_back(combination);
	}
	combinationsWithoutComboNum = combine(nums_tmp, k);
	for (int j = 0; j < combinationsWithoutComboNum.size(); j++)
	{
		vector<int> combination = combinationsWithoutComboNum[j];
		combinations.push_back(combination);
	}
	return combinations;
}
vector<vector<int> > subsets(vector<int> &S) {
    sort(S.begin(), S.end());
    vector<vector<int>> subsets;
	for (int i = 0; i <= S.size(); i++)
    {
		vector<vector<int>> subsets_tmp = combine(S, i);
		subsets.insert(subsets.end(), subsets_tmp.begin(), subsets_tmp.end());	
    }
	return subsets;
}