subsets ii
基本上，您必须打印所有唯一子集。例如，如果nums = [1,2,2]，则res = [[], [1], [1, 2], [2], [2,2], [1,2,2]]
我的代码给出res = [[], [1], [1, 2], [2]]

def subsets_dfs(nums):
    nums.sort()
    res = []
    def dfs(nums, res, cur, pos):
        res.append(cur)
        for i in range(pos, len(nums)):
            if i > 0 and nums[i] == nums[i-1]:
                continue
            dfs(nums, res, cur + [nums[i]], i + 1)
    dfs(nums, res, [], 0)
    return res