78 Subsets

Given a set ofdistinctintegers,nums, return all possible subsets (the power set).

Note:The solution set must not contain duplicate subsets.

Example:

Input:
 nums = [1,2,3]

Output:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

class Solution {
    public List<List<Integer>> subsets(int[] nums) {

        List<List<Integer>> ans = new ArrayList<>();
        if (nums == null ){
            return ans;
        }
        if (nums.length == 0) {
            ans.add(new ArrayList<Integer>());
            return ans;
        }
        Arrays.sort(nums);
        List<Integer> sub = new ArrayList<Integer>();
        helper(ans, sub, nums, 0);
        return ans;
    }
    public void helper(List<List<Integer>> ans, List<Integer> sub, int[] nums, int startIdx) {
        ans.add(new ArrayList<Integer>(sub));
        if (startIdx == nums.length) {
            return;
        }
        for (int i = startIdx; i < nums.length; i++) {
            sub.add(nums[i]);
            helper(ans, sub, nums, i+1);
            sub.remove(sub.size() - 1);
        }
    }
}

**** Thing is you really do not understand what is subset!!

ans.add(new ArrayList<>(sub));
        if (startIdx == nums.length) {
           return;
        }