90. Subsets II

public void traverse(List<List<Integer>> resultList, List<Integer> currentList, int index, int[] nums) {
    resultList.add(new ArrayList<Integer>(currentList)); // 3. add currentList to final result list
    for(int i = index; i < nums.length; i++) {
        if( i > index && nums[i] == nums[i - 1] ) // 2. duplicate removal
            continue;
        currentList.add(nums[i]);
        traverse(resultList, currentList, i + 1, nums);
        currentList.remove(currentList.size() - 1);
    }
}

public List<List<Integer>> subsetsWithDup(int[] nums) {
    Arrays.sort(nums); // 1. sort the array
    List<List<Integer>> resultList = new ArrayList<List<Integer>>();
    traverse(resultList, new ArrayList<Integer>(), 0, nums);
    return resultList;
}