[Leetcode] Subsets

A classical problem.

Given a set of distinct integers, nums, return all possible subsets.

Note: The solution set must not contain duplicate subsets.

For example,
If nums = [1,2,3], a solution is:

[
  [3],
  [1],
  [2],
  [1,2,3],
  [1,3],
  [2,3],
  [1,2],
  []
]

And a classical solution:

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class Solution(object): def subsets(self, nums): """ :type nums: List[int] :rtype: List[List[int]] """ res = [] output = [] self.helper(nums, 0, res, output) return res def helper(self, nums, pos, res, output): if pos == len(nums): res.append(list(output)) else: self.helper(nums, pos+1, res, output) output.append(nums[pos]) self.helper(nums, pos+1, res, output) output.pop()

但我感觉我需要再仔细想想为什么最后一步要pop，为什么append里面需要deepcopy of output list...