JavaScript链表结构——双向链表

JavaScript链表结构——双向链表

//双向链表类
function DoublyLinkList(){
	//节点类
	function Node(data){
		this.data = data
		this.pre = null
		this.next = null
	}
	//初始化属性
	this.head = null
	this.tail = null
	this.length = 0
	/*
	*
	* 1.append方法,在双链表尾部添加新节点
	* 
	*/
	DoublyLinkList.prototype.append = function(data){
		let node = new Node(data)
		//判断当前链表是否为空
		if (this.length == 0){
			this.head = node
			this.tail = node
		}
		else{
			node.prev = this.tail
			this.tail.next = node
			this.tail = node
		}
		//链表长度+1
		this.length += 1
	}
	/*
	*
	* 2.1 toString方法
	* 
	*/
	DoublyLinkList.prototype.toString = function(){
		return this.backwardString()
	}
	/*
	*
	* 2.2 forwardString方法,从后向前返回字符串形式的数据
	* 
	*/
	DoublyLinkList.prototype.forwardString = function(){
		let listString = ''
		let current = this.tail
		while(current != null){
			listString += current.data + ' '
			current = current.prev
		}
		return listString
	}
	/*
	*
	* 2.3 backwardString方法，从前向后返回字符串形式的数据
	* 
	*/
	DoublyLinkList.prototype.backwardString = function(){
		let listString = ''
		let current = this.head
		while(current != null){
			listString += current.data + ' '
			current = current.next
		}
		return listString
	}
	/*
	*
	* 3. insert方法，指定位置插入节点
	* 
	*/
 DoublyLinkList.prototype.insert = function(data, position){	
	 //判断position是否越界
	 if (position < 0 || position > this.length){
		 return false
	 }
	 //新建节点对象
	 let node = new Node(data)
	 //1.判断插入位置是否为头部
	 if (position == 0){
		 //1.1判断当前链表是否为空
		 if (this.length == 0){
			 this.tail = node
		 }
		 //1.2当前链表不为空时
		 else{
			 this.head.prev = node
			 node.next = this.head
		 }
		 //无论当前链表是否为空,head都重新指向新节点
		 this.head = node
	 }
	 //2.判断插入位置是否为尾部
	 else if (position == this.length){
		 this.append(data)
	 }
	 //3.插入的位置既不是头部也不是尾部
	 else{
		 let current = null
		 //3.1 插入的位置离头部比较近
		 if (position <= this.length/2 - 1){
			 current = this.head
			 let index = 0
			 //找到要插入的位置
			 while (index < position){
				 current = current.next
				 index ++
			 }
		 }
		 //3.2 插入的位置离尾部比较近
		 else {
			 current = this.tail
			 let index = this.length - 1
			 //找到要插入的位置
			 while (index > position){
				 current = current.prev
				 index --
			 }
		 }
		 //改变指针指向
		 node.next = current
		 node.prev = current.prev
		 current.prev.next = node
		 current.prev = node
	 }
	 //链表长度+1
	 this.length += 1
 }
 /*
 *
 * 4. get方法，查找指定位置的节点的数据
 * 
 */
 DoublyLinkList.prototype.get = function(position){
	 //越界判断
	 if (position < 0 || position >= this.length){
		 return null
	 }
	 
	 let current = null
	 //查找的位置离头部比较近
	 if (position <= this.length/2 -1){
		 current = this.head
		 let index = 0
		 while (index < position){
			 current = current.next
			 index ++
		 }
	 }
	 //查找的位置离尾部比较近
	 else {
		 current = this.tail
		 let index = this.length - 1
		 while (index > position){
			 current = current.prev
			 index --
		 }
	 }
	 return current.data
 }
 /*
 *
 * 5. indexOf方法,通过数据查找对应的索引
 * 
 */ 
 DoublyLinkList.prototype.indexOf = function(data){
	 let current = this.head
	 let index = 0
	 while (current != null){
		 if (current.data == data){
			 //找到返回index
			 return index
		 }
		 current = current.next
		 index ++
	 }
	 //没找到返回-1
	 return -1
 }
 /*
 *
 * 6. update方法，更新指定位置的节点的数据
 * 
 */ 
  DoublyLinkList.prototype.update = function(newData, position){
		if (position < 0 || position >= this.length){
			return false
		}
		let current = null
		if (position <= this.length/2 -1){
			current = this.head
			let index = 0
			while (index < position){
				current = current.next
				index ++
			}
		}
		else {
			current = this.tail
			let index = this.length - 1
			while (index > position){
				current = current.prev
				index --
			}
		}
		//打印数据变化
		console.log(current.data + '=>' + newData)
		current.data = newData
	}
	/*
	*
	* 7. removeAt方法,移除指定位置的节点
	* 
	*/
	DoublyLinkList.prototype.removeAt = function(position){
		if (position < 0 || position >= this.length){
			return null
		}
		
		let current = this.head
		
		//1. 移除的位置为头部
		if (position == 0){
			//1.1 链表的长度为1
			if (this.length == 1){
				this.head = null
				this.tail = null
			}
			//1.2 链表的长度不为1
			else {
				this.head.next.prev = null
				this.head = this.head.next
			}
		}
		//2. 移除的位置为尾部
		else if (position == this.length -1){
			current = this.tail
			this.tail.prev.next = null
			this.tail = this.tail.prev
		}
		//3. 移除的位置不是头部或尾部
		else {
			//3.1 从头部开始寻找
			if (position <= this.length -1){
				current = this.head
				let index = 0
				while (index < position){
					current = current.next 
					index ++
				}
			}
			//3.2 从尾部开始寻找
			else {
				current = this.tail
				let index = this.length -1
				while (index > position){
					current = current.prev 
					index --
				}
			}
			//改变指针指向
			current.prev.next = current.next
			current.next.prev = current.prev
		}
		//链表长度-1
		this.length -= 1
		//返回删除的数据
		return current.data
	}
	/*
	*
	* 8. remove方法，移除指定数据的节点
	* 
	*/ 
	DoublyLinkList.prototype.remove = function(data){
		let index = this.indexOf(data)
		return this.removeAt(index)
	}
	
}