"""

Given a collection of integers that might contain duplicates, nums,

return all possible subsets.

Note: The solution set must not contain duplicate subsets.

For example,

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

[

[2],

[1],

[1,2,2],

[2,2],

[1,2],

[]

]

"""

def subsets_unique(nums):

def backtrack(res, nums, stack, pos):

if pos == len(nums):

res.add(tuple(stack))

else:

# take

stack.append(nums[pos])

backtrack(res, nums, stack, pos+1)

stack.pop()

# don't take

backtrack(res, nums, stack, pos+1)

res = set()

backtrack(res, nums, [], 0)

return list(res)

test = [1, 2, 2]

print(test)

print(subsets_unique(test))