leetcode JAVA Subsets 难度系数3 3.27

Question：

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],
[]
]

public class Solution {
public ArrayList<ArrayList<Integer>> subsets(int[] S) {
ArrayList<ArrayList<Integer>> results = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> result = new ArrayList<Integer>();
Arrays.sort(S);
dfs(S,result,0,results);
return results;
}

private void dfs(int[] s, ArrayList<Integer> result, int step,
ArrayList<ArrayList<Integer>> results) {
if(step==s.length){
ArrayList<Integer> path = new ArrayList<Integer>(result);
results.add(path);
return;
}
dfs(s,result,step+1,results);
result.add(s[step]);
dfs(s,result,step+1,results);
result.remove(result.size()-1);

}
}

第二次：

public class Solution {
public ArrayList<ArrayList<Integer>> subsets(int[] S) {
ArrayList<ArrayList<Integer>> results = new ArrayList<ArrayList<Integer>>();
ArrayList<Integer> result = new ArrayList<Integer>();
Arrays.sort(S);
dfs(S,0,result,results);
return results;
}

private void dfs(int[] num, int step, ArrayList<Integer> result,
ArrayList<ArrayList<Integer>> results) {
results.add(new ArrayList<Integer>(result));
for(int i=step;i<num.length;i++){
result.add(num[i]);
dfs(num, i+1, result, results);
result.remove(result.size()-1);
}
}
}