90. Subsets II

Given an integer array nums that may contain duplicates, return all possible

subsets

(the power set).

The solution set must not contain duplicate subsets. Return the solution in any order.

Example 1:

Input: nums = [1,2,2]
Output: [[],[1],[1,2],[1,2,2],[2],[2,2]]

Example 2:

Input: nums = [0]
Output: [[],[0]]

Solution:

class Solution {
    public List<List<Integer>> subsetsWithDup(int[] nums) {
        List<List<Integer>> result = new ArrayList<List<Integer>>();
        if (nums == null || nums.length == 0){
            return result;
        }

        Arrays.sort(nums);

        int index = 0;
        List<Integer> subResult = new ArrayList<Integer>();
        helper(nums, index, subResult, result);
        return result;
    }

    private static void helper(int[] nums, int index, List<Integer> subResult, List<List<Integer>> result){
        // base case
        if (index == nums.length){
            result.add(new ArrayList<Integer>(subResult));
            return;
        }

        // add
        subResult.add(nums[index]);
        helper(nums, index + 1, subResult, result);

        subResult.remove(subResult.size() - 1);
        while(index < nums.length -1  && nums[index] == nums[index + 1]){
            index++;
        }

        helper(nums, index + 1, subResult, result);
    } 
}


/*

1. sort the nums first


                1  2  2
                /         \
               1           -
             /    \         /   \
            1,2    1       2      -
           /  \    /  \    / \    / \
        1,2,2 1,2 [1,2] 1 2,2 2   [2]  -


skip the duplicate nums until not duplicate



// TC: O(n * branch^level) = O(n * 2 ^n)
// SC: O(n)

*/