0199. Binary Tree Right Side View

# 199. Binary Tree Right Side View#

## 题目 #

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom.

Example:

``````
Input: [1,2,3,null,5,null,4]
Output: [1, 3, 4]
Explanation:

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

``````

## 解题思路 #

• 这一题是按层序遍历的变种题。按照层序把每层的元素都遍历出来，然后依次取每一层的最右边的元素即可。用一个队列即可实现。
• 第 102 题和第 107 题都是按层序遍历的。

## 代码 #

``````
package leetcode

/**
* Definition for a binary tree node.
* type TreeNode struct {
*     Val int
*     Left *TreeNode
*     Right *TreeNode
* }
*/
func rightSideView(root *TreeNode) []int {
res := []int{}
if root == nil {
return res
}
queue := []*TreeNode{root}
for len(queue) > 0 {
n := len(queue)
for i := 0; i < n; i++ {
if queue[i].Left != nil {
queue = append(queue, queue[i].Left)
}
if queue[i].Right != nil {
queue = append(queue, queue[i].Right)
}
}
res = append(res, queue[n-1].Val)
queue = queue[n:]
}
return res
}

``````

Apr 8, 2023