题解 | #从上往下打印二叉树#

# class TreeNode:

#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param root TreeNode类 
# @return int整型一维数组
#
class Solution:
    def PrintFromTopToBottom(self , root: TreeNode) -> List[int]:
        # write code here
        if root is None:
            return []
        res = []
        queue = [root]

        while queue:
            for _ in range(len(queue)):
                note = queue.pop(0) 
                if note.left:
                    queue.append(note.left)
                if note.right:
                    queue.append(note.right)
                res.append(note.val)
        
        return res