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。

public class Solution {
    public List<List<Integer>> subsets(int[] S) {
            List<List<Integer>> lastList=new ArrayList<>();
            List<Integer> nonSet= new ArrayList<>();
            lastList.add(nonSet);
            if (S==null || S.length==0) {
            return lastList;
            }
            Arrays.sort(S);
            
            for (int i = 0; i < S.length; i++) {
                List<List<Integer>> tempList=new ArrayList<>();         
            for (List<Integer> list : lastList) {
                    List<Integer> currlist=new ArrayList<>();
                    currlist.addAll(list);
                    currlist.add(S[i]);
                    tempList.add(currlist);
            }
            lastList.addAll(tempList);
            }
            return lastList;
    }
}