90. Subsets II

Given a collection of integers that might contain duplicates, nums, return all possible subsets.

Note: 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],
  []
]

 此题以前做过类似的题目，不做解释，代码如下：

public class Solution {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        List<List<Integer>> res= new ArrayList<>();
        Arrays.sort(nums);
        helper(res,new ArrayList<Integer>(),nums,0);
        return res;
    }
    public void helper(List<List<Integer>> res,List<Integer> list,int[] nums,int index){
        if(!res.contains(list)){
            res.add(new ArrayList<Integer>(list));
        }
        for(int i=index;i<nums.length;i++){
            list.add(nums[i]);
            helper(res,list,nums,i+1);
            list.remove(list.size()-1);
        }
        return;
        
    }
}