題幹：

給定一組不含重複元素的整數陣列 nums，返回該陣列所有可能的子集（冪集）。

說明：解集不能包含重複的子集。

示例:

輸入: nums = [1,2,3]
輸出:
[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

演算法思想：與77題大致相同

class Solution:

    def subsets(self, nums):
        """
        :type nums: List[int]
        :rtype: List[List[int]]
        """
        result = []
        temp = []
        length = len(nums)
        result = self.helper(0, length, nums, temp, result)
        return result

    def helper(self, level, len, nums, temp, result):
        for i in range(level, len, 1):
            temp.append(nums[i])
            result.append(temp[:])
            self.helper(i + 1, len, nums, temp, result)
            temp.pop()
        #result.append([])
        return result


s = Solution()
res = s.subsets([1, 2, 3])
print(res)