go语言在区块链编程中有巨大的优势，其中fabric和ethereum都是基于go语言编写的。为了能更好的学习区块链的底层技术，先将go的基础打好。

本篇文章使用golang来实现树的遍历

树的定义

package tree

type Node struct {
    Val int
    Left *Node
    Right *Node
}

深度优先遍历

深度优先遍历需要优先使用栈

栈的定义

type Stack struct {
    list *list.List
} 

func NewStack() *Stack {
    list := list.New()
    return &Stack{list}
}

func (stack *Stack) Push(value interface{}) {
    stack.list.PushBack(value)
}

func (stack *Stack) Pop() interface{} {
    if e := stack.list.Back(); e!= nil {
        stack.list.Remove(e)
        return e.Value
    }
    
    return nil
}

func (stack *Stack) Len() int {
    return stack.list.Len()
}

func (stack *Stack) Empty() bool {
    return stack.Len() == 0
}

前序遍历

为Stack结构体添加前序遍历的方法，前序遍历的思路是通过栈，将右子树先行压栈，然后左子树压栈

func (root *Node) PreTravesal() {
    if root == nil {
        return
    }
    
    s := stack.NewStack()
    s.push(root)
    
    for !s.Empty() {
        cur := s.Pop().(*Node)
        fmt.Println(cur.Val)
        
        if cur.Right != nil {
            s.Push(cur.Right)
        }
        if cur.Left != nil {
            s.Push(cur.Left)
        }
    }
}

中序遍历

func (root *Node) InTravesal() {
    if root == nil {
        return
    }
    
    s := stack.NewStack()
    cur := root
    for {
        for cur != nil {
            s.Push(cur)
            cur = cur.Left
        }
        
        if s.Empty() {
            break
        }
        
        cur = s.Pop().(*Node)
        fmt.Println(cur.Val)
        cur = cur.right
    }
}

后序遍历

func (root *Node) PostTravesal() {
    if root == nil {
        return
    }
    
    s := stack.NewStack()
    out := stack.NewStack()
    s.Push(root)
    
    for !s.Empty() {
        cur := s.Pop().(*Node)
        out.Push(cur)
        
        if cur.Left != nil {
            s.Push(cur.Left)
        }
        
        if cur.Right != nil {
            s.Push(cur.Right)
        }
    }
    
    for !out.Empty() {
        cur := out.Pop().(*Node)
        fmt.Println(cur.Val)
    }
}

广度优先遍历

广度优先遍历需要使用到队列

实现队列

使用切片实现队列

package queue

import (
    "fmt"
)

type Queue interface {
    Offer(e interface{})
    Poll() interface{}
    Clear() bool
    Size() int
    IsEmpty() bool
}

type LinkedList struct {
    elements []interface{}
}

func New() *LinkedList {
    return &LinkedList{}
}


func (queue *LinkedList) Offer(e interface{}) {
    queue.elements = append(queue.elements, e)
}

func (queue *LinkedList) Poll() interface{} {
    if queue.IsEmpty() {
        fmt.Println("Poll error : queue is Empty")
        return nil
    }

    firstElement := queue.elements[0]
    queue.elements = queue.elements[1:]
    return firstElement
}

func (queue *LinkedList) Size() int {
    return len(queue.elements)
}

func (queue *LinkedList) IsEmpty() bool {
    return len(queue.elements) == 0
}

func (queue *LinkedList) Clear() bool  {
    if queue.IsEmpty() {
        fmt.Println("queue is Empty!")
        return false
    }
    for i := 0; i < queue.Size(); i++ {
        queue.elements[i] = nil
    }
    queue.elements = nil
    return true
}

层序遍历

func (root *Node) LevelTravesal() {
    if root == nil {
        return
    }

    linkedList := queue.New()
    linkedList.Offer(root)

    for !linkedList.IsEmpty()  {
        cur := linkedList.Poll().(*Node)
        fmt.Println(cur.Val)

        if cur.Left != nil {
            linkedList.Offer(cur.Left)
        }

        if cur.Right != nil {
            linkedList.Offer(cur.Right)
        }
    }
}

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