单链表、循环链表的JS实现

数据结构系列前言：

数据结构作为程序员的基本知识，需要我们每个人牢牢掌握。近期我也展开了对数据结构的二次学习，来弥补当年挖的坑。。。。。。   当时上课的时候也就是跟着听课，没有亲自实现任何一种数据结构，更别提利用数据结构来解决问题了。  现在就来填坑了   在这里提醒看到我博客的孩子们，如果你还是在校生，永远不要轻视任何一门基础课的学习，这个时候挖的坑，要么需要用双倍的努力去填，要么会直接影响一个人的能力等等。。。。。。
千万别给自己挖坑

进入正题，关于链表的数据结构知识，这里简单介绍下：

链表是一种物理存储单元上非线性、非连续性的数据结构（它在数据逻辑上是线性的），它的每个节点由两个域组成：数据域和指针域。数据域中存储实际数据，指针域则存储着指针信息，指向链表中的下一个元素或者上一个元素。正是由于指针的存在，链表的存储在物理单元是非连续性的。

链表的优点和缺点同样明显。和线性表相比，链表在添加和删除节点上的效率更高，因为其只需要修改指针信息即可完成操作，而不像线性表（数组）那样需要移动元素。同样的，链表的长度在理论上也是无限的（在存储器容量范围内），并可以动态变化长度，相比线性表优势很大。 相应的，由于线性表无法随机访问节点，只能通过指针顺着链表进行遍历查询来访问，故其访问数据元素的效率比较低。

下面是JS部分

这里面封装了的常用方法及描述：

方法	描述
append(element)	向链表尾部添加结点element
insert(position,element)	向位置position处插入结点element
removeAt(position)	按照索引值position删除结点
remove(element)	搜索并删除给定结点element
remove()	删除链表中最后一个结点
indexOf(element)	查找并返回给定结点element的索引值
isEmpty()	判断链表是否为空
size()	获取链表长度
toString()	转换为字符串输出
getHead()	获取头结点
getTail()	获取尾结点

对于各常用方法的算法描述在这里就不写了，相信大家都可以轻易读懂并理解，毕竟都是非常基础的知识了。

单链表：

function LinkedList(){
	/*节点定义*/
	var Node = function(element){
		this.element = element; //存放节点内容
		this.next = null; //指针
	}

	var length = 0, //存放链表长度
	    head = null; //头指针

	this.append = function(element){
	 	var node = new Node(element),
	 	    current; //操作所用指针

	 	if (!head){
	 		head = node;
	 	}else {
	 		current = head;

	 		while(current.next){
	 			current = current.next;
	 		}

	 		current.next = node;
	 	}

	 	length++;
	 	return true;
	};

	this.insert = function(position, element){
	 	if (position >= 0 && position <= length) {
	 		var node = new Node(element),
		 		current = head,
		 		previous,
		 		index = 0;

	 		if(position === 0){
	 			node.next = current;
	 			head = node;
	 		}else{
	 			while(index++ < position){
	 				previous = current;
	 				current = current.next;
	 			}
	 			node.next = current;
	 			previous.next = node;
	 		}

	 		length++;
	 		return true;
	 	}else{
	 		return false;
	 	}
	 };

	this.removeAt = function(position){
	 	if(position > -1 && position < length){
	 		var current = head,
	 		    previous,
	 		    index = 0;

	 		if (position === 0) {

	 			head = current.next;

	 		}else{

	 			while (index++ < position){
	 				previous = current;
	 				current = current.next;
	 			}

	 			previous.next = current.next;
	 		};

	 		length--;
	 		return current.element;
	 	}else{
	 		return null;
	 	}
	};

	this.remove = function(element){
	 	var current = head,
	 	    previous;

	 	if(element === current.element){
	 		head = current.next;
	 		length--;
	 		return true;
	 	}
	 	previous = current;
	 	current = current.next;

	 	while(current){
	 		if(element === current.element){
	 			previous.next = current.next;
	 			length--;
	 			return true;
	 		}else{
	 			previous = current;
	 			current = current.next;
	 		}
	 	}
	 	return false;
	};

	this.remove = function(){
	 	if(length < 1){
	 		return false;
	 	}

	 	var current = head,
 		previous;

	 	if(length == 1){
	 		head = null;
	 		length--;
	 		return current.element;
	 	}

	 	while(current.next !== null){
	 		previous = current;
	 		current = current.next;
	 	}

	 	previous.next = null;
	 	length--;
	 	return current.element;
	};

	this.indexOf = function(element){
	 	var current = head,
	 	    index = 0;

	 	while(current){
	 		if(element === current.element){
	 			return index;
	 		}
	 		index++;
	 		current = current.next;
	 	}

	 	return false;
	};

	this.isEmpty = function(){
	 	return length === 0;
	};

	this.size = function(){
	 	return length;
	};

	this.toString = function(){
	 	var current = head,
	 	    string = '';

	 	while(current){
	 		string += current.element;
	 		current = current.next;
	 	}
	 	return string;
	};	 

	this.getHead = function(){
	 	return head;
	}

}

循环链表：在单链表的基础上，将尾节点的指针指向头结点，就构成了一个循环链表。环形链表从任意一个节点开始，都可以遍历整个链表。

function CircularLinkedList(){
	var Node = function(element){
		this.element = element;
		this.next = null;
	}

	var length = 0,
	    head   = null;

	this.append = function(element){
		var node = new Node(element),
		    current;

		if (!head) {
			head = node;
			node.next = head;
		}else{
			current = head;

			while(current.next !== head){
				current = current.next;
			}

			current.next = node;
			node.next = head;
		};

		length++;
		return true;
	};

	this.insert = function(position, element){
		if(position > -1 && position < length){
			var node = new Node(element),
			    index = 0,
			    current = head,
			    previous;

			if (position === 0) {

				node.next = head;
				head = node;

			}else{

				while(index++ < position){
					previous = current;
					current = current.next;
				}

				previous.next = node;
				node.next = current;

			};

			length++;
			return true;
		}else{
			return false;
		}
	};

	this.removeAt = function(position){
		if(position > -1 && position < length){
	 		var current = head,
	 		    previous,
	 		    index = 0;

	 		if (position === 0) {

	 			head = current.next;

	 		}else{

	 			while (index++ < position){
	 				previous = current;
	 				current = current.next;
	 			}

	 			previous.next = current.next;
	 		};

	 		length--;
	 		return current.element;
	 	}else{
	 		return null;
	 	}
	};

	this.remove = function (element){
		var current = head,
		    previous,
		    indexCheck = 0;

		while(current && indexCheck < length){
			if(current.element === element){
				if(indexCheck == 0){
					head = current.next;
					length--;
					return true;
				}else{
					previous.next = current.next;
					length--;
					return true;
				}
			}else{
				previous = current;
				current = current.next;
				indexCheck++;
			}
		}
		return false;
	};

	this.remove = function(){
		if(length === 0){
			return false;
		}

		var current = head,
		    previous,
		    indexCheck = 0;

		if(length === 1){
			head = null;
			length--;
			return current.element;
		}

		while(indexCheck++ < length){
			previous = current;
			current = current.next;
		}
		previous.next = head;
		length--;
		return current.element;
	};

	this.indexOf = function(element){
		var current = head,
		    index = 0;

		while(current && index < length){
			if(current.element === element){
				return index;
			}else{
				index++;
				current = current.next;
			}
		}
		return false;
	};

	this.isEmpty = function(){
	 	return length === 0;
	};

	this.size = function(){
	 	return length;
	};

	this.toString = function(){
	 	var current = head,
	 	    string = '',
	 	    indexCheck = 0;

	 	while(current && indexCheck < length){
	 		string += current.element;
	 		current = current.next;
	 		indexCheck++;
	 	}

	 	return string;
	};	 

}

使用方法：

在外部扩充方法：

因为每次遍历所做的操作都是不同的，所以遍历方法我都是在使用环境中用类扩充方法现写进去，方法如下

关于双向链表与双向循环链表，见本人另一篇博客：  双向链表、双向循环链表的JS实现

对于链表的封装，完整版地址：https://github.com/zhuwq585/Data-Structure-in-JavaScript/blob/master/LinkedList.js