LeetCode—subsets（子集dfs）—java

题目描述：

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],
  []
]

思路解析：

• 新加入一个字符，就可以把list保存到res中，然后回溯
• 注意保持序列的顺序，还要加上[]
• 参考：https://www.cnblogs.com/springfor/p/3879830.html

代码：

import java.util.*;
public class Solution {
    public ArrayList> subsets(int[] S) {
        ArrayList> res = new ArrayList>();
        if(S==null||S.length==0){
            return res;
        }
        ArrayList list = new ArrayList();
        Arrays.sort(S);
        res.add(new ArrayList());
        dfs(S,0,list,res);
        return res;
    }
    public static void dfs(int[] S,int start,ArrayList list,ArrayList> res){
        for(int i=start;i(list));
            dfs(S,i+1,list,res);
            list.remove(list.size()-1);
        }
    }
}