SubsetsII

Given a collection of integers that might contain duplicates, S, 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 S = [1,2,2], a solution is:

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