# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

#
# 
# @param root TreeNode類 
# @return int整型二維陣列
#
class Solution:
    def levelOrder(self , root ):
        # write code here
        result = []
        if not root:
            return result
        queue = []
        queue.append(root)
        while queue:
            tem = []
            length = len(queue)
            for i in range(length):
                node = queue.pop(0)
                tem.append(node.val)
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
            result.append(tem)
        return result
 

https://www.nowcoder.com/practice/04a5560e43e24e9db4595865dc9c63a3?tpId=188&&tqId=36551&rp=1&ru=/ta/job-code-high-week&qru=/ta/job-code-high-week/question-ranking
https://leetcode-cn.com/problems/binary-tree-level-order-traversal/solution/die-dai-di-gui-duo-tu-yan-shi-102er-cha-shu-de-cen/