Subsets [LeetCode]

Given a set of distinct integers, S, return all possible subsets.

Note:

Elements in a subset must be in non-descending order.
The solution set must not contain duplicate subsets.

For example,
If S = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

Summary: Recursive approach, we can optimize it.

 1     vector<vector<int> > subsets(vector<int> &S) {
 2         std::sort(S.begin(), S.end());
 3         vector<vector<int> > result;
 4         vector<int> subset;
 5         result.push_back(subset);
 6         if(S.size() == 0)
 7             return result;
 8         for(int i = 0; i < S.size(); i ++) {
 9             vector<int> sub_s(S.begin() + i + 1, S.end());
10             vector<vector<int> > ret = subsets(sub_s);
11             for(auto item : ret){
12                 item.insert(item.begin(), S[i]);
13                 result.push_back(item);
14             }
15         }
16         
17         return result;
18     }