Write a method to return all subsets of a set. The elements in a set are pairwise distinct.

Note: The result set should not contain duplicated subsets.

Example:

 Input:  nums = [1,2,3]
 Output: 
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]