102. Binary Tree Level Order Traversal [easy] (Python)

题目链接

https://leetcode.com/problems/binary-tree-level-order-traversal/

题目原文

Given a binary tree, return the level order traversal of its nodes’ values. (ie, from left to right, level by level).

For example:
Given binary tree {3,9,20,#,#,15,7},

    3
   / \
  9  20
    /  \
   15   7

return its level order traversal as:

[
  [3],
  [9,20],
  [15,7]
]

题目翻译

给定一个二叉树，返回所有节点值的层序遍历结果。（从左到右，从