LeetCode Q78: Subsets *

Given a set of distinct integers, nums, return all possible subsets.

Note:

• Elements in a subset must be in non-descending order.
• The solution set must not contain duplicate subsets.

For example,
If nums = [1,2,3], a solution is:

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

Solution 1:

Solution 2
Solution 3 (recursion)
Solution 4 (Bit manipulation)

Round 2 solution:
Idea is simple, similar to Q77, don't wait until the last to save the result, instead we save intermediate results in every recursion.