劍指offer 從上往下打印二叉樹

題目

從上往下打印出二叉樹的每個節點，同層節點從左至右打印。

思路

層次遍歷

代碼

# -*- coding:utf-8 -*-
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None
class Solution:
    # 返回從上到下每個節點值列表，例：[1,2,3]
    def PrintFromTopToBottom(self, root):
        # write code here
        res_list = []
        queue = []
        if root: queue.append(root)
        while queue:
            root = queue[0]
            queue.pop(0)
            res_list.append(root.val)
            if root.left: queue.append(root.left)
            if root.right: queue.append(root.right)
        return res_list