// 定义链表所有操作
var linklist = function(){
    //定义结点
    var Node = function(element){
        this.element = element
        this.next = null
    }

    //定义头指针为空
    var head = null
    var length = 0
    
    //向链表尾追加元素
    this.append = function(element){
        var node = new Node(element)
        if(head == null){
            head = node
        }
        else{
            var current = head
            while(current.next != null){
                current = current.next
            }
            current.next = node;
        }
        length++;
    }

    //向链表中间插入内容
    this.insert = function(position,element){
        var node = new Node(element)
        if(position == 0){
            var current = head
            head = node;
            head.next = current
        }
        else{
            var previous = null
            var index = 0
            var current = head
            while(index < position){
                previous = current;
                current = current.next;
                index++;
            }
            node.next = current;
            previous.next = node;
        }
        length++;
    }

    //根据索引位置删除链表元素
    this.removeAt = function(position){
        if(position < 0 || position > length){
            return -1;
        }
        else{
            var current = head
            var index = 0
            var previous = null
            while(index < position){
                previous = current;
                current = current.next;
                index++
            }
            previous.next = current.next;
        }
        length--;
    }

    //根据值返回其索引值
    this.indexof = function(element){
        var current = head
        var index = 0
        while(current){
            if(current.element === element)
            return index;
            current = current.next;
            index++;
        }
        return -1;
    }

    //根据值删除其链表内容
    this.remove = function(element){
        return this.removeAt(this.indexof(element));
    }

    //返回链表头部内容
    this.gethead = function(){
        return head;
    }
}