LeetCode 078 Subsets

题目

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

1 典型的DFS+回溯

2 注意题目要求不能递减，所以递归前先排序不要忘记

3 按照坐标的增长来递归即可。

代码

public class Solution {
public ArrayList<ArrayList<Integer>> subsets(int[] S) {
ArrayList<ArrayList<Integer>> ans = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> temp = new ArrayList<Integer>();
Arrays.sort(S);
ans.add(temp);
useme(ans,temp,0,S);
return ans;
}

public void useme(ArrayList<ArrayList<Integer>> ans,ArrayList<Integer> temp,int start,int[] S){
for(int i=start;i<S.length;i++){
temp.add(S[i]);
ans.add(new ArrayList<Integer>(temp));
useme(ans,temp,i+1,S);
temp.remove(temp.size()-1);
}
}
}