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 void helper(List> res, List item, int start, int[] nums, boolean[] isVisited) {
        for(int i = start; i < nums.length; i ++) {
            if(i > start && nums[i] == nums[i - 1])
                continue;
            if(!isVisited[i]) {
                item.add(nums[i]);
                isVisited[i] = true;
                res.add(new ArrayList(item));
                helper(res, item, i + 1, nums, isVisited);
                isVisited[i] = false;
                item.remove(item.size() - 1);
            }
        }
    }

    //It can only can use the solution 1 of Subsets 1
    public List> subsetsWithDup(int[] nums) {
        List> res = new ArrayList<>();
        if(nums == null || nums.length == 0)
            return res;
        Arrays.sort(nums);
        res.add(new ArrayList<>());
        helper(res, new ArrayList(), 0, nums, new boolean[nums.length]);
        return res;
    }
}