题目：

给定一棵二叉树，想象自己站在它的右侧，按照从顶部到底部的顺序，返回从右侧所能看到的节点值。

示例:

输入: [1,2,3,null,5,null,4]
输出: [1, 3, 4]
解释:

   1            <---
 /   \
2     3         <---
 \     \
  5     4       <---

题目的理解：

二叉树按行来观察的话，那就是最后的node排序成数组。

python实现

from typing import List

# Definition for a binary tree node.
class TreeNode:
    def __init__(self, x):
        self.val = x
        self.left = None
        self.right = None

class Solution:
    def rightSideView(self, root: TreeNode) -> List[int]:
        if root is None:
            return []

        rowNode = [root]
        result = [root.val]

        while len(rowNode) > 0:
            rowNodeTemp = list()
            for node in rowNode:
                if node is not None:
                    if node.left is not None:
                        rowNodeTemp.append(node.left)
                    if node.right is not None:
                        rowNodeTemp.append(node.right)
            if len(rowNodeTemp) > 0:
                result.append(rowNodeTemp[-1].val)
            rowNode = rowNodeTemp

        return result

想看最优解法移步此处