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
