[数据结构与算法]JavaScript数据结构双向链表的封装

    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
      }
    }