package main

 import "fmt"

 type Object interface{}

 type Node struct {

     data Object

     next *Node

 }

 type List struct {

     headNode *Node

 }

 func NewNode(data Object, next *Node) *Node {

     return &Node{data, next}

 }

 func (list *List) IsEmpty() bool {

     return list.headNode == nil

 }

 func (list *List) Add(node *Node) *List {

     headNode := list.headNode

     if headNode.next != nil {

         node.next = headNode.next

     }

     headNode.next = node

     return list

 }

 func (list *List) Append(node *Node) *List {

     if list.IsEmpty() {

         list.headNode = node

         return list

     }

     curNode := list.headNode

     for curNode.next != nil {

         curNode = curNode.next

     }

     curNode.next = node

     return list

 }

 func (list *List) Insert(index int, data Object) {

     if (index >=  && index < list.Length()) {

         count :=

         if !list.IsEmpty() {

             curNode := list.headNode

             for curNode != nil && count < index {

                 count++

                 curNode = curNode.next

             }

             node := NewNode(data, curNode.next)

             curNode.next = node

         }

     }

 }

 func (list *List) Remove(index int) {

     if (index >=  && index < list.Length()) {

         count :=

         if !list.IsEmpty() {

             curNode := list.headNode

             for curNode != nil && count < index- {

                 count++

                 curNode = curNode.next

             }

             curNode.next = curNode.next.next

         }

     }

 }

 func PrintList(list *List) {

     cur := list.headNode

     for cur != nil {

         fmt.Println(cur.data)

         cur = cur.next

     }

 }

 func (list *List) Length() int {

     var length int

     curNode := list.headNode

     for curNode != nil {

         length++

         curNode = curNode.next

     }

     return length

 }

 func ReverseList(head *Node) *Node {

     cur := head

     var pre *Node = nil

     for cur != nil {

         pre, cur, cur.next = cur, cur.next, pre

     }

     return cur

 }

 func main(){

     fmt.Println("NewNode======================")

     node := NewNode(, nil)

     fmt.Println(node.data)

     list := &List{node}

     PrintList(list)

     node2 := NewNode("a", nil)

     list.Append(node2)

     fmt.Println("Add======================")

     PrintList(list)

     node1 := NewNode(, nil)

     list.Add(node1)

     fmt.Println("Length======================")

     PrintList(list)

     fmt.Println(list.Length())

     fmt.Println("Insert======================")

     list.Insert(, )

     PrintList(list)

     fmt.Println("Remove======================")

     list.Remove()

     PrintList(list)

     fmt.Println("ReverseList======================")

     ReverseList(node)

     PrintList(list)

 }