js创建链表

首先要明确，我们为什么要创建链表呢？数组的大小是固定的，从数组的起点或中间插入或移除的成本很高，因为需要移动元素。尽管JS的Array类方法可以做这些，但是情况也是这样。链表存储有序的元素集合，但不同于数组，链表中的元素在内存中并不是连续放置的。每个元素由一个存储元素本身和指向下一个元素的指针组成。

相对于传统的数组，链表的一个好处在于，添加或移除元素的时候不需要移动其他元素。然而，链表需要使用指针，因此实现链表时需要额外注意。数组的另一个细节是可以直接访问任何位置的任何元素，而要想访问链表中间的一个元素，需要从起点（表头）开始迭代到列表直到找到所需元素。

好了，闲话少叙，正式创建链表！
我们使用动态原型模式来创建一个链表。列表最后一个节点的下一个元素始终是null。

function LinkedList() {
    //先创建一个节点
    function Node(element) {
        this.element = element;
        this.next = null;
    }
    this.head = null;
    this.length = 0;

    //通过对一个方法append判断就可以知道是否设置了prototype
    if ((typeof this.append !== 'function') && (typeof this.append !== 'string')) {
        //添加元素
        LinkedList.prototype.append = function(element) {
            var node = new Node(element);
            var current;

            if (this.head == null) {
                this.head = node;
            } else {
                current = this.head;
                while (current.next != null) {
                    current = current.next;
                }
                current.next = node;
            }
            this.length++;
        };

        //插入元素，成功true，失败false
        LinkedList.prototype.insert = function(position, element) {
            if (position > -1 && position < this.length) {
                var current = this.head;
                var node = new Node(element);
                var previous;
                var index = 0;
                if (position == 0) {
                    node.next = current;
                    this.head = node;
                } else {
                    while (index++ < position) {
                        previous = current;
                        current = current.next;
                    }
                    node.next = current;
                    previous.next = node;
                }
                this.length++;
                return true;
            } else {
                return false;
            }
        };

        //根据位置删除指定元素，成功 返回元素， 失败 返回null
        LinkedList.prototype.removeAt = function(position) {
            if (position > -1 && position < this.length) {
                var current = this.head;
                var previous = null;
                var index = 0;

                if (position == 0) {
                    this.head = current.next;
                } else {
                    while (index++ < position) {
                        previous = current;
                        current = current.next;
                    }
                    previous.next = current.next;
                }
                this.length--;
                return current.element;
            } else {
                return null;
            }
        };

        //根据元素删除指定元素，成功 返回元素， 失败 返回null
        LinkedList.prototype.remove = function(element) {
            var index = this.indexOf(element);
            return this.removeAt(index);
        };

        //返回给定元素的索引，如果没有则返回-1
        LinkedList.prototype.indexOf = function(element) {
            var current = this.head;
            var index = 0;
            while (current) {
                if (current.element === element) {
                    return index;
                }
                current = current.next;
                index++;
            }
            return -1;
        };

        LinkedList.prototype.isEmpty = function() {
            return this.length === 0;
        };
        LinkedList.prototype.size = function() {
            return this.length;
        };
        LinkedList.prototype.toString = function() {
            var string = '';
            var current = this.head;
            while (current) {
                string += current.element;
                current = current.next;
            }
            return string;
        };
        LinkedList.prototype.getHead = function() {
            return this.head;
        };
    }
}

链表的基本使用

var linkedList = new LinkedList();
    console.log(linkedList.isEmpty());//true;
    linkedList.append('huang');
    linkedList.append('du')
    linkedList.insert(1,'cheng');
    console.log(linkedList.toString());//huangchengdu
    console.log(linkedList.indexOf('du'));//
    console.log(linkedList.size());//
    console.log(linkedList.removeAt(2));//du
    console.log(linkedList.toString());//huangcheng

创建双向链表

在双向链表中,链接是双向的:一个链向下一个元素, 另一个链向前一个元素。

双向链表和链表的区别就是有一个tail属性，所以必须重写insert、append、removeAt方法。每个节点对应的Node也多了一个prev属性。

//寄生组合式继承实现，详见javascript高级程序设计第七章
   function inheritPrototype(subType, superType) {
       function object(o) {
           function F() {}
           F.prototype = o;
           return new F();
       }
       var prototype = object(superType.prototype);
       prototype.constructor = subType;
       subType.prototype = prototype;
   }
   function DoublyLinkedList() {
       function Node(element) {
           this.element = element;
           this.next = null;
           this.prev = null;
       }
       this.tail = null;
       LinkedList.call(this);
       //与LinkedList不同的方法自己实现。
       this.insert = function(position, element) {
           if (position > -1 && position <= this.length) {
               var node = new Node(element);
               var current = this.head;
               var previous;
               var index = 0;
               if (position === 0) {
                   if (!this.head) {
                       this.head = node;
                       this.tail = node;
                   } else {
                       node.next = current;
                       current.prev = node;
                       this.head = node;
                   }
               } else if (position == this.length) {
                   current = this.tail;
                   current.next = node;
                   node.prev = current;
                   this.tail = node;
               } else {
                   while (index++ < position) {
                       previous = current;
                       current = current.next;
                   }
                   previous.next = node;
                   node.next = current;
                   current.prev = node;
                   node.prev = previous;
               }
               this.length++;
               return true;
           } else {
               return false;
           }
       };
       this.append = function(element) {
           var node = new Node(element);
           var current;
           if (this.head === null) {
               this.head = node;
               this.tail = node;
           } else {
               current = this.head;
               while (current.next !== null) {
                   current = current.next;
               }
               current.next = node;
               node.prev = current;
               this.tail = node;
           }
           this.length++;
       };
       this.removeAt = function(position) {
           if (position > -1 && position < this.length) {
               var current = this.head;
               var previous;
               var index = 0;
               if (position === 0) {
                   this.head = current.next;
                   if (this.length === 1) {
                       this.tail = null;
                   } else {
                       this.head.prev = null;
                   }
               } else if (position === (this.length - 1)) {
                   current = this.tail;
                   this.tail = current.prev;
                   this.tail.next = null;
               } else {
                   while (index++ < position) {
                       previous = current;
                       current = current.next;
                   }
                   previous.next = current.next;
                   current.next.prev = previous;
               }
               this.length--;
               return current.element;
           } else {
               return false;
           }
       };
   }
   inheritPrototype(DoublyLinkedList, LinkedList);

双向链表的基本使用

var doublyList = new DoublyLinkedList();
    console.log(doublyList.isEmpty()); //true;
    doublyList.append('huang');
    doublyList.append('du')
    doublyList.insert(1, 'cheng');
    console.log(doublyList.toString()); //huangchengdu
    console.log(doublyList.indexOf('du')); //
    console.log(doublyList.size()); //
    console.log(doublyList.removeAt(2)); //du
    console.log(doublyList.toString()); //huangcheng