线性表-双向链表

    public class twoWayLinkList<T> {
    
        public int N;
    
        public Node head;
        public Node last;
    
    
        public static void main(String[] args) {
            twoWayLinkList<String> s = new twoWayLinkList<>();
            s.insert("测试");
            s.insert("测试2");
            s.insert("测试3");
            s.insert(2, "我");
            System.out.println(s.getFirst());
            System.out.println(s.get(2));
            System.out.println(s.length());
        }
        //结点类
        private class Node{
            //数据
            T item;
            //指向结点
                //上一个
            Node pre;
                //下一个
            Node next;
    
            public Node(T item, Node pre,Node next){
                this.item = item;
                this.pre = pre;
                this.next = next;
            }
        }
        //初始化
        public twoWayLinkList(){
            N = 0;
            //无前驱和后继
            head  = new Node(null, null, null);
            last = null;
        }
    
        //清除
        public void clear(){
            this.head.next = null;
            this.last.pre = null;
            N = 0;
        }
    
        //是否为空
        public boolean isempty(){
            return N==0;
        }
    
        //长度
        public int length(){
            return N;
        }
    
        //获取i位置处的元素t
        public T get(int i){
            Node n = head;
            //找新节点的前一个结点
            for (int index = 0; index < i; index++) {
                n = n.next;
            }
            return n.item;
        }
    
        //获取第一个元素
        public T getFirst(){
            if(isempty()){
                return null;
            }
            return head.next.item;
        }
    
        //获取最后一个元素
        public T getLast(){
            if(isempty()){
                return null;
            }
            return last.item;
        }
    
        //插入
        public void insert(T t){
            //是否为空
            if (isempty()){
                Node newNode = new Node(t, head, null);
                last = newNode;
                head.next = last;
            }else {
                Node oldLast = last;
                Node newNode = new Node(t, oldLast, null);
                oldLast.next = newNode;
                last = newNode;
            }
            N++;
        }
    
        //向i位置处插入元素t
        public void insert(int i ,T t){
            //默认不为空
            Node n = head;
            //找新节点的前一个结点
            for (int index = 0; index < i-1; index++) {
                n = n.next;
            }
            //原位置处的结点
            Node originalNode = n.next;
            //创建新结点
            Node newNode = new Node(t, n, originalNode);
            originalNode.pre = newNode;
            n.next = newNode;
            N++;
        }
    
        //删除并返回删除的元素
        public T delete(int i){
            //默认不为空
            Node n = head;
            //找新节点的前一个结点
            for (int index = 0; index < i-1; index++) {
                n = n.next;
            }
            return head.item;
        }
    }