学习JavaScript数据结构与算法（四）——循环链表

循环链表可以向普通链表一样只有单向引用，也可以像双向链表一样有双向引用。

循环链表和普通链表的区别就在于，循环链表的最后一个元素指向下一个元素的指针（tail.next）不是引用null，而是指向第一个元素（head）。

双向循环链表有指向head元素的tail.next，和指向tail元素的head.prev。

function CircularLinkedList() {    var Node = function(element){        this.element = element;        this.next = null;    };    var length = 0;    var head = null;    this.append = function(element){        var node = new Node(element),            current;        //向为空的列表添加一个元素        if (head === null){            head = node;        }        else {            current = head;            //循环列表，直到找到最后一项            //列表的最后一个节点的下一个元素指向head而不是null            while(current.next !== head){                current = current.next;            }            //找到最后一项，将其next赋为node，建立链接            current.next = node;        }        //将插入的节点的next赋为head，建立链接        node.next = head;        length++;//更新列表的长度    };    this.insert = function(position, element){        //检查越界值        if (position >= 0 && position <= length){            var node = new Node(element),                current = head,                previous,                index = 0;            //在列表的起点添加一个元素            if (position === 0){                //如果列表中没有节点                if(!head){                    head = node;                    node.next = head;                }                else {                    node.next = current;                    //更新最后一个元素                    while(current.next !== head){                        current = current.next;                    }                    head = node;                    current.next = head;                }            }            //在列表中间或尾部添加一个元素            else {                while (index++ < position){                    previous = current;                    current = current.next;                }                node.next = current;                previous.next = node;            }            length++;//更新列表长度            return true;        }        //越界就返回false，表示没有添加项到列表中        else {            return false;        }    };    this.removeAt = function(position){        //检查越界值        if (position > -1 && position < length){            var current = head,                previous,                index = 0;            //移除第一项            if (position === 0){                while(current.next !== head){                    current = current.next;                }                head = head.next;                current.next = head;            }            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 index = this.indexOf(element);        return this.removeAt(index);    };    this.indexOf = function(element){        var current = head,            index = -1;        //检查第一项        if (element == current.element){            return 0;        }        index++;        //检查列表中的元素        while(current.next !== head){            if (element == current.element){                return index;            }            current = current.next;            index++;        }        //检查最后一项        if (element == current.element){            return index;        }        return -1;    };    this.isEmpty = function() {        return length === 0;    };    this.size = function() {        return length;    };    this.getHead = function(){        return head;    };    this.toString = function(){        var current = head,            s = current.element;        while(current.next !== head){            current = current.next;            s += ', ' + current.element;        }        return s.toString();    };    this.print = function(){        console.log(this.toString());    };}

测试代码如下：

var circularLinkedList = new CircularLinkedList();circularLinkedList.append(15);circularLinkedList.print();circularLinkedList.append(16);circularLinkedList.print();circularLinkedList.insert(0,14);circularLinkedList.print();circularLinkedList.insert(1,14.5);circularLinkedList.print();circularLinkedList.insert(4,17);circularLinkedList.print();circularLinkedList.removeAt(0);circularLinkedList.print();circularLinkedList.removeAt(1);circularLinkedList.print();circularLinkedList.removeAt(2);circularLinkedList.print();console.log(circularLinkedList.indexOf(14.5));console.log(circularLinkedList.indexOf(16));

在控制台上输出结果如下：