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Commit f5c845b

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# [199. 二叉树的右视图](https://leetcode-cn.com/problems/binary-tree-right-side-view/description/)
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### 题目描述
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<p>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。</p>
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<p><strong>示例:</strong></p>
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<pre><strong>输入:</strong>&nbsp;[1,2,3,null,5,null,4]
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<strong>输出:</strong>&nbsp;[1, 3, 4]
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<strong>解释:
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</strong>
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1 &lt;---
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/ \
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2 3 &lt;---
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\ \
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5 4 &lt;---
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</pre>
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### 解题思路
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1. BFS
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### 具体解法
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#### **Golang**
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```go
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type TreeNode struct {
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Val int
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Left *TreeNode
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Right *TreeNode
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}
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func rightSideView(root *TreeNode) []int {
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res := []int{}
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if root == nil {
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return res
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}
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queue := []*TreeNode{root}
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res = []int{root.Val}
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for len(queue) > 0 {
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l := len(queue)
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flag := 0
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for i := 0; i < l; i++ {
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node := queue[i]
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if node.Right != nil {
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if flag == 0 {
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flag = node.Right.Val
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}
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queue = append(queue, node.Right)
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}
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if node.Left != nil {
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if flag == 0 {
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flag = node.Left.Val
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}
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queue = append(queue, node.Left)
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}
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}
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if flag != 0 {
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res = append(res, flag)
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}
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queue = queue[l:]
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}
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return res
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}
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```
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package leetcode
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/*
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* @lc app=leetcode.cn id=199 lang=golang
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*
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* [199] 二叉树的右视图
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*/
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// @lc code=start
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/**
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* Definition for a binary tree node.
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* type TreeNode struct {
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* Val int
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* Left *TreeNode
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* Right *TreeNode
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* }
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*/
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type TreeNode struct {
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Val int
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Left *TreeNode
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Right *TreeNode
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}
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func rightSideView(root *TreeNode) []int {
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res := []int{}
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if root == nil {
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return res
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}
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queue := []*TreeNode{root}
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res = []int{root.Val}
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for len(queue) > 0 {
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l := len(queue)
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flag := 0
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for i := 0; i < l; i++ {
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node := queue[i]
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if node.Right != nil {
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if flag == 0 {
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flag = node.Right.Val
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}
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queue = append(queue, node.Right)
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}
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if node.Left != nil {
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if flag == 0 {
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flag = node.Left.Val
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}
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queue = append(queue, node.Left)
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}
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}
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if flag != 0 {
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res = append(res, flag)
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}
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queue = queue[l:]
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}
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return res
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}
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// @lc code=end
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package leetcode
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import (
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"testing"
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)
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func TestRightSideView(t *testing.T) {
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root := &TreeNode{
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Val: 1,
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Left: &TreeNode{
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Val: 2,
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Left: nil,
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Right: nil,
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},
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Right: nil,
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}
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ret := []int{1, 2}
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nums := rightSideView(root)
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for i, v := range nums {
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if ret[i] != v {
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t.Fatalf("case fails %v\n", ret)
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}
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}
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root1 := &TreeNode{}
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nums1 := rightSideView(root1)
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if len(nums1) > 1 {
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t.Fatalf("case fails %v\n", nums1)
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}
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root2 := &TreeNode{
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Val: 1,
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Left: &TreeNode{
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Val: 2,
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Left: nil,
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Right: nil,
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},
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Right: &TreeNode{
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Val: 3,
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Left: &TreeNode{
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Val: 5,
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Left: nil,
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Right: nil,
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},
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Right: &TreeNode{
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Val: 6,
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Left: nil,
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Right: nil,
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},
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},
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}
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ret2 := []int{1, 3, 6}
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nums2 := rightSideView(root2)
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for i, v := range nums2 {
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if ret2[i] != v {
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t.Fatalf("case fails %v\n", nums2)
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}
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}
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}

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