new_contents: """Leetcode 102. Binary Tree Level Order Traversal
  Medium
  
  URL: https://leetcode.com/problems/binary-tree-level-order-traversal/
  
  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,null,null,15,7],
      3
     / \
    9  20
      /  \
     15   7
  return its level order traversal as:
  [
    [3],
    [9,20],
    [15,7]
  ]
  """
  
  # Definition for a binary tree node.
  class TreeNode(object):
      def __init__(self, val):
          self.val = val
          self.left = None
          self.right = None
  
  
  class Solution(object):
      def levelOrder(self, root):
          """
          :type root: TreeNode
          :rtype: List[List[int]]
          """
          pass
  
  
  def main():
      pass
  
  
  if __name__ == '__main__':
      main()
  
subject: Add lc0102_binary_tree_level_order_traversal.py