Subsets II

def subsetsWithDup(nums):
    res = []
    nums.sort()
    
    def backtrack(i, subset):
        if i == len(nums):
            res.append(subset[::])
            return
            
        # All subsets that include nums[i]
        subset.append(nums[i])
        backtrack(i + 1, subset)
        subset.pop()
        
        # All subsets that don't include nums[i]
        while i + 1 < len(nums) and nums[i] == nums[i + 1]:
            i += 1
        backtrack(i + 1, subset)
        
    backtrack(0, [])
    return res