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++;  
            }  
        }     
    }  
}