定义

在计算机科学中，链表是数据元素的线性集合，其每个元素都指向下一个元素，元素存储上并不连续。

双向链表，每个元素知道其上一个元素和下一个元素。

以下为示例代码：

package com.tfq.arithmetic.linkedlist;import java.util.Iterator;
import java.util.function.Consumer;/*** @author: fqtang* @date: 2024/05/21/9:29* @description: 双向链表(带哨兵)*/
public class DoubleLinkedListSentinel implements Iterable<Integer> {static class Node {Node prev;//上一个节点指针int value;//值Node next;//下一个节点指针public Node(Node prev, int value, Node next) {this.prev = prev;this.next = next;this.value = value;}}private Node head;//头哨兵private Node tail;//尾哨兵public DoubleLinkedListSentinel() {this.head = new Node(null, 666, null);this.tail = new Node(null, 999, null);head.next = tail;tail.prev = head;}/*** 返回链表第一种方式** @return*/public void loop(Consumer<Integer> consumer) {Node p = head.next;while(p != null) {consumer.accept(p.value);p = p.next;}}/*** 返回链表第二种方式** @return*/public void loop2(Consumer<Integer> consumer) {for(Node p = head.next; p != null; p = p.next) {consumer.accept(p.value);}}public void addFirst(int value) {insert(0, value);}public void addLast(int value) {Node last = tail.prev;Node insertNode = new Node(last, value, tail);last.next = insertNode;tail.prev = insertNode;}private Node findLast() {return tail.prev;}public void removeLast() {Node remove = tail.prev;if(remove == head) {throw new IllegalArgumentException(String.format("双向链表为空，不能删除此链表的头部!"));}Node prev = remove.prev;prev.next = tail;tail.prev = prev;}/*** 根据索引查找链表的节点** @param index* @return*/private Node findNode(int index) {int i = -1;for(Node p = head; p != tail; p = p.next, i++) {if(i == index) {return p;}}return null;//没找到}public int getValue(int index) {Node node = findNode(index - 1);if(node == head || node == tail) {throw new IllegalArgumentException(String.format("index [%d] 不合法%n", index));}return findNode(index - 1).value;}/*** 向索引位置插值** @param index 索引* @param value 待插入值*/public void insert(int index, int value) {//找到上一个节点和下一个节点Node prev = findNode(index - 1);if(prev == null) {throw new IllegalArgumentException(String.format("index [%d] 不合法%n", index));}Node next = prev.next;//创建一个要插入的新节点Node insertedNode = new Node(prev, value, next);prev.next = insertedNode;next.prev = insertedNode;}/*** 删除第一个节点*/public void removeFirst() {remove(0);}/*** 根据索引删除指定元素** @param index 待删除索引*/public void remove(int index) {Node prev = findNode(index - 1);if(prev == null) {throw new IllegalArgumentException(String.format("index [%d] 不合法%n", index));}Node removed = prev.next;if(removed == tail) {throw new IllegalArgumentException(String.format("index [%d] 不合法,已删除尾部 %n", index));}Node next = removed.next;prev.next = next;next.prev = prev;}/*** 返回链表第三种方式** @return*/@Overridepublic Iterator<Integer> iterator() {return new Iterator<Integer>() {Node p = head.next;@Overridepublic boolean hasNext() {return p != tail;}@Overridepublic Integer next() {int v = p.value;p = p.next;return v;}};}
}