1. 环形链表：

                 

2. 建议先不要看我写得自己先实现下，只将Node内部类复制自己命名得容器内，

    实现方法：

                     a. add方法（添加到头部，尾部添加，指定位置添加）

                     b. get方法（获取首部，获取尾部，获取指定位置）

                     c. remove方法（删除首部，删除尾部，删除指定位置）

                     d. size方法（手动维护一个size变量，实现0(1)复杂度 ）

                     e. 迭代器（实现迭代器，能够循环遍历）

     手动实现之后（每个功能只实现一种也可以），再回头参照，思考下即可！  

package com.nami.algorithm.study.day05;import java.io.Serializable;
import java.util.Iterator;
import java.util.function.Consumer;/*** 环形双向哨兵链表* 非线程安全* beyond u self and trust u self.** @Author: lbc* @Date: 2023-09-01 9:07* @email: 594599620@qq.com* @Description: keep coding*/
public class RingLinkedList<E> implements Serializable, Iterable<E>, Cloneable {/*** 容器已添加的元素*/private int size = 1;/*** 哨兵节点*/private Node sentinel = new Node(null, "-1", null);/*** 初始化哨兵*/public RingLinkedList() {this.sentinel.prev = this.sentinel;this.sentinel.next = this.sentinel;}/*** 向链表添加数据** @param element 添加的元素*/public void addFirst(E element) {Node first = this.sentinel;Node next = first.next;Node node = new Node<>(first, element, next);first.next = node;next.prev = node;++this.size;}/*** 向链表尾部添加数据** @param element*/public void addLast(E element) {Node last = this.sentinel.prev;Node node = new Node<>(last, element, sentinel);last.next = node;sentinel.prev = node;++this.size;}/*** 获取容器指定位置的值** @param index* @return*/public E get(int index) {if (index > size - 1) {throw new IndexOutOfBoundsException("元素不存在");}Node next = sentinel.next;for (int i = 0; i < index; next = next.next, i++) {}if (sentinel == next) {throw new IndexOutOfBoundsException(String.format("index [%d] 不合法%n", index));}return (E) next.value;}/*** 获取指定位置节点node** @param index* @return*/private Node getNode(int index) {Node next = sentinel.next;for (int i = 0; i < index; next = next.next, i++) {}return next;}/*** 向元素指定节点添加值** @param index* @param e*/public void add(int index, E e) {if (index > size - 1) {throw new IndexOutOfBoundsException("元素不存在");}Node node = getNode(index);Node prev = node.prev;Node node1 = new Node(prev, e, node);node.prev = node1;prev.next = node1;++this.size;}/*** 移除容器内第一个元素*/public void removeFirst() {Node node = getNode(0);if (sentinel == node) {throw new IndexOutOfBoundsException(String.format("index [%d] 不合法%n", 0));}Node prev = node.prev;Node next = node.next;prev.next = next;next.prev = prev;--this.size;}/*** 删除第一个元素*/public void removeFirst0() {Node removed = this.sentinel.next;if (removed == this.sentinel) {throw new IndexOutOfBoundsException("容器内已无元素");}Node next = removed.next;this.sentinel.next = next;next.prev = this.sentinel;}/*** 移除容器内指定位置元素** @param index*/public void remove(int index) {if (index > size - 1) {throw new IndexOutOfBoundsException(String.format("index [%d] 不合法%n", index));}Node node = getNode(index);if (sentinel == node) {throw new IndexOutOfBoundsException(String.format("index [%d] 不合法%n", 0));}Node prev = node.prev;Node next = node.next;prev.next = next;next.prev = prev;--this.size;}/*** 删除最后一个节点*/public void removeLast() {Node prev = this.sentinel.prev;if (prev == this.sentinel) {return;}Node next = prev.next;Node prev0 = prev.prev;prev0.next = next;next.prev = prev0;--this.size;}/*** 获取容器大小** @return*/public int size() {return this.size - 1;}/*** 迭代器遍历** @return*/@Overridepublic Iterator iterator() {return new NodeIterator();}/*** 匿名内部类* 内部类使用到了外部类的成员变量时，不能使用static修饰*/private class NodeIterator implements Iterator {Node node = sentinel.next;@Overridepublic boolean hasNext() {return node != sentinel;}@Overridepublic Object next() {Object value = node.value;node = node.next;return value;}}/*** while实现** @param consumer*/public void forEach(Consumer consumer) {Node firstNode = this.sentinel.next;while (firstNode != sentinel) {consumer.accept(firstNode.value);firstNode = firstNode.next;}}/*** Node类型 节点对象* 二者为组合关系，所以 由外部类变为内部类，对外隐藏实现细节*/private static class Node<E> {/*** 上一个节点*/private Node<E> prev;/*** 值*/private E value;/*** 下一个节点*/private Node<E> next;public Node(Node<E> prev, E value, Node<E> next) {this.prev = prev;this.value = value;this.next = next;}}}