LeetCode Subsets

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],
  []
]

思路是，每次添加一个元素，就是在上一次的基础上，对每个列表加入元素，再与上一次的合并。

 1 public class Solution {
 2     public List<List<Integer>> subsets(int[] S) {
 3             List<List<Integer>> lastList=new ArrayList<>();
 4             List<Integer> nonSet= new ArrayList<>();
 5             lastList.add(nonSet);
 6             if (S==null || S.length==0) {
 7             return lastList;
 8             }
 9             Arrays.sort(S);
10             
11             for (int i = 0; i < S.length; i++) {
12                 List<List<Integer>> tempList=new ArrayList<>();         
13             for (List<Integer> list : lastList) {
14                     List<Integer> currlist=new ArrayList<>();
15                     currlist.addAll(list);
16                     currlist.add(S[i]);
17                     tempList.add(currlist);
18             }
19             lastList.addAll(tempList);
20             }
21             return lastList;
22     }
23 }