解决思路

回溯+剪枝

class Solution {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        List<List<Integer>> res = new ArrayList<>();
        if (nums == null || nums.length == 0)
            return res;
        //先排序
        Arrays.sort(nums);
        backtrack(0,nums,res,new ArrayDeque<>());
        return res;
    }
    private void backtrack(int begin,int[] nums,List<List<Integer>> res,Deque<Integer> temp){
        res.add(new ArrayList<>(temp));
        for (int i = begin;i < nums.length;i++){
            //剪枝
            if (i > begin && nums[i] == nums[i - 1])
                continue;
            temp.addLast(nums[i]);
            backtrack(i + 1,nums,res,temp);
            temp.removeLast();
        }
    }
}