满足以下两个条件的树就是二叉树：
- 本身是有序树
- 树中包含的各个节点的度不能超过 2，即只能是 0、1 或者 2
1. 前序遍历
前序遍历二叉树（根左右）
package main
import "fmt"
type Student struct {
Name string
Age int
Score float32
// 左子树指针
left *Student
// 右子树指针
right *Student
}
func main() {
// 根节点
var root Student
root.Name = "root"
root.Age = 10
root.Score = 90
// 一级左子树
var left1 Student
left1.Name = "left1"
left1.Age = 20
left1.Score = 80
root.left = &left1
// 一级右子树
var right1 Student
right1.Name = "right1"
right1.Age = 30
right1.Score = 70
root.right = &right1
// 二级左子树
var left2 Student
left2.Name = "left2"
left2.Age = 40
left2.Score = 60
left1.left = &left2
// 调用前序遍历函数
Req(&root)
}
func Req(p *Student) {
if p == nil {
return
}
fmt.Println(p)
// 遍历左子树
Req(p.left)
// 遍历右子树
Req(p.right)
}
&{
root 10 90 0xc000078360 0xc000078390}
&{
left1 20 80 0xc0000783c0 <nil>}
&{
left2 40 60 <nil> <nil>}
&{
right1 30 70 <nil> <nil>}
2. 中序遍历
中序遍历二叉树（左根右）
package main
import "fmt"
type Student struct {
Name string
Age int
Score float32
// 左子树指针
left *Student
// 右子树指针
right *Student
}
func main() {
// 根节点
var root Student
root.Name = "root"
root.Age = 10
root.Score = 90
// 一级左子树
var left1 Student
left1.Name = "left1"
left1.Age = 20
left1.Score = 80
root.left = &left1
// 一级右子树
var right1 Student
right1.Name = "right1"
right1.Age = 30
right1.Score = 70
root.right = &right1
// 二级左子树
var left2 Student
left2.Name = "left2"
left2.Age = 40
left2.Score = 60
left1.left = &left2
// 调用中序遍历函数（left,root,right）
Req(&root)
}
func Req(p *Student) {
if p == nil {
return
}
// 遍历左子树
Req(p.left)
// 输出 root 节点
fmt.Println(p)
// 遍历右子树
Req(p.right)
}
&{
left2 40 60 <nil> <nil>}
&{
left1 20 80 0xc0000783c0 <nil>}
&{
root 10 90 0xc000078360 0xc000078390}
&{
right1 30 70 <nil> <nil>}
3. 后序遍历
后序遍历二叉树（左右根）
package main
import "fmt"
type Student struct {
Name string
Age int
Score float32
// 左子树指针
left *Student
// 右子树指针
right *Student
}
func main() {
// 根节点
var root Student
root.Name = "root"
root.Age = 10
root.Score = 90
// 一级左子树
var left1 Student
left1.Name = "left1"
left1.Age = 20
left1.Score = 80
root.left = &left1
// 一级右子树
var right1 Student
right1.Name = "right1"
right1.Age = 30
right1.Score = 70
root.right = &right1
// 二级左子树
var left2 Student
left2.Name = "left2"
left2.Age = 40
left2.Score = 60
left1.left = &left2
// 调用中序遍历函数（left,root,right）
Req(&root)
}
func Req(p *Student) {
if p == nil {
return
}
// 遍历左子树
Req(p.left)
// 遍历右子树
Req(p.right)
// 输出 root 节点
fmt.Println(p)
}
&{
left2 40 60 <nil> <nil>}
&{
left1 20 80 0xc0000783c0 <nil>}
&{
right1 30 70 <nil> <nil>}
&{
root 10 90 0xc000078360 0xc000078390}