LeetCode 078 Subsets

题目

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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

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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

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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);        }    }}