function DoublyLinkedList() {
function Node(data){
this.next = null
this.prev = null
this.data = data
}
this.head = null
this.tail = null
this.length = 0
DoublyLinkedList.prototype.append = function(data) {
var newNode = new Node(data)
if (this.length === 0){
this.head = newNode
this.tail = newNode
}else{
newNode.prev = this.tail
this.tail.next = newNode
this.tail = newNode
}
this.length++
}
DoublyLinkedList.prototype.toString = function() {
return this.forwardString()
}
DoublyLinkedList.prototype.backwardString = function() {
var current = this.tail
var listString = ''
while(current) {
listString += current.data + ''
current = current.prev
}
return listString
}
DoublyLinkedList.prototype.forwardString = function() {
var current = this.head
var listString = ''
while (current) {
listString += current.data + ''
current = current.next
}
return listString
}
DoublyLinkedList.prototype.insert = function(data, position) {
if (position < 0 || position > this.length) return false
var newNode = new Node(data)
if (this.length === 0) {
this.head = newNode
this.tail = newNode
}else{
if (position === 0) {
newNode.next = this.head
this.head.prev = newNode
this.head = newNode
}else if(position == this.length){
newNode.prev = this.tail
this.tail.next = newNode
this.tail = newNode
}
else {
var current = this.head
var previous = null
var index = 0
while(index++ < position){
previous = current
current = current.next
}
newNode.next = current
current.prev = newNode
previous.next = newNode
newNode.prev = previous
}
}
this.length++
}
DoublyLinkedList.prototype.get = function(position) {
if (position < 0 || position >= this.length) return null
var index = 0
var current = this.head
while (index++ < position) {
current = current.next
}
return current
}
DoublyLinkedList.prototype.indexOf = function(data) {
var index = 0
var current = this.head
while(current) {
if (current.data === data) {
return index
}
current = current.next
index++
}
return -1
}
DoublyLinkedList.prototype.update = function(data, position) {
if (position < 0 || position >= this.length) return false
var index = 0
var current = this.head
while (index++ < position) {
current = current.next
}
current.data = data
return true
}
DoublyLinkedList.prototype.removeAt = function (position) {
if (position < 0 || position >= this.length) return null
var index = 0
var current = this.head
var previous = null
if (this.length === 1) {
this.head = null
this.tail = null
}else{
if (position === 0) {
this.head = this.head.next
this.head.next.prev = null
}else if(position == this.length-1) {
current = this.tail
this.tail = this.tail.prev
this.tail.prev.next = null
}else {
while (index++ < position) {
current = current.next
}
current.prev.next = current.next
current.next.prev = current.prev
}
}
this.length--
return current.data
}
DoublyLinkedList.prototype.remove = function(data) {
var position = this.indexOf(data)
return this.removeAt(position)
}
DoublyLinkedList.prototype.isEmpty = function() {
if (this.length) return true
return false
}
DoublyLinkedList.prototype.size = function() {
return this.length
}
}