BinaryTreeRightSideView.py

# -*- coding: utf-8 -*-
# @File    : BinaryTreeRightSideView.py
# @Date    : 2020-02-29
# @Author  : tc
"""
题号 199. 二叉树的右视图
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       <---

参考：https://leetcode-cn.com/problems/binary-tree-right-side-view/solution/er-cha-shu-de-you-shi-tu-by-leetcode/
"""
from typing import List
from collections import deque

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 not root:
            return []
        res,queue = [],[root]
        while queue:
            temp = 0
            n = len(queue)
            for i in range(n):
                node = queue.pop(0)
                temp = node.val
                if node.left:
                    queue.append(node.left)
                if node.right:
                    queue.append(node.right)
            res.append(temp)
        return res

    def rightSideView2(self, root):
        rightmost_value_at_depth = dict()  # depth -> node.val
        max_depth = -1

        queue = deque([(root, 0)])
        while queue:
            node, depth = queue.popleft()

            if node is not None:
                # maintain knowledge of the number of levels in the tree.
                max_depth = max(max_depth, depth)

                # overwrite rightmost value at current depth. the correct value
                # will never be overwritten, as it is always visited last.
                rightmost_value_at_depth[depth] = node.val

                queue.append((node.left, depth + 1))
                queue.append((node.right, depth + 1))

        return [rightmost_value_at_depth[depth] for depth in range(max_depth + 1)]


if __name__ == '__main__':
    root = TreeNode(3)
    node1 = TreeNode(9)
    node2 = TreeNode(20)
    node3 = TreeNode(15)
    node4 = TreeNode(7)

    root.left = node1
    root.right = node2
    node2.left = node3
    node2.right = node4

    solution = Solution()
    print(solution.rightSideView(root))