leetcode--Subsets II

Given a collection of integers that might contain duplicates, nums, 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 nums =

[1,2,2]

, a solution is:

[
[2],
[1],
[1,2,2],
[2,2],
[1,2],
[]
]

public class Solution {
public List<List<Integer>> subsetsWithDup(int[] nums) {
List<List<Integer>> res = new ArrayList<List<Integer>>();
if(nums.length==0) return res;
Arrays.sort(nums);
helper(nums, 0, new ArrayList<Integer>(), res);
return res;
}

public void helper(int[] nums, int level, List<Integer> item, List<List<Integer>> res) {
res.add(new ArrayList<Integer>(item));
for(int i=level;i<nums.length;i++){
item.add(nums[i]);
helper(nums,i+1,item,res);
item.remove(item.size()-1);
//跳过相同的元素
while(i<(nums.length-1)&&nums[i]==nums[i+1]) {
i++;
}
}
}
}