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