（三）Java数据结构之单链表（增删改查，末尾/有序添加、打印倒数第几个、反转链表、合并有序链表）_javalist 倒数第一个

先看代码：

package top.baikunlong.top.baikunlong.linkedlist;
 
import java.util.ArrayList;
import java.util.Collections;
 
/**
 * @author baikunlong
 * @date 2020/10/8 10:26
 */
public class SingleLinkedList {
 
    /**
     * 头指针
     */
    private Node head = new Node(0, "头指针");
 
    /**
     * 在最后添加节点
     *
     * @param node
     */
    public void add(Node node) {
        //首先找到最后个节点
        Node temp = head;//头节点不能移动，需要临时变量
        while (true) {
            if (temp.next == null) {//如果是最后个则添加
                temp.next = node;
                break;
            } else {
                temp = temp.next;//否则移动到下一个节点
            }
        }
    }
 
    /**
     * 根据序号插入
     *
     * @param node
     */
    public void addByNo(Node node) {
        Node temp = this.head;
        while (true) {
            if (temp.next == null) {//如果到了链表尾部，直接添加
                temp.next = node;
                return;
            } else if (temp.next.no > node.no) {//如果当前节点的next.no大于node.no，则在当前节点后添加node
                node.next = temp.next;
                temp.next = node;
                return;
            } else if (temp.next.no == node.no) {
                //如果等于则提示已存在
                System.out.printf("已存在 no=%d 的节点\n", node.no);
                return;
            }
            //如果均不是则往下遍历
            temp = temp.next;
        }
    }
 
    /**
     * 根据no删除
     *
     * @param no
     */
    public void deleteByNo(int no) {
        Node temp = this.head;
        while (true) {
            if (temp.next == null) {
                System.out.printf("节点为 no=%d 不存在\n", no);
                return;
            }
            if (temp.next.no == no) {
                temp.next = temp.next.next;
                return;
            }
            temp = temp.next;
        }
    }
 
    /**
     * 根据no更新
     *
     * @param node
     */
    public void updateByNo(Node node) {
        Node temp = this.head.next;
        while (true) {
            if (temp == null) {
                System.out.printf("节点为 no=%d 不存在\n", node.no);
                return;
            } else if (temp.no == node.no) {
                temp.name = node.name;
                return;
            }
            temp = temp.next;
        }
    }
 
    /**
     * 根据no获取
     *
     * @param no
     * @return
     */
    public Node getNodeByNo(int no) {
        Node temp = this.head.next;
        while (true) {
            if (temp == null) {
                throw new RuntimeException("节点为 no=" + no + " 不存在");
            } else if (temp.no == no) {
                return temp;
            }
            temp = temp.next;
        }
    }
 
    /**
     * 打印链表
     */
    public void list() {
        if (head.next == null) System.out.println("链表为空");
        Node temp = head.next;
        while (true) {
            if (temp == null) {
                break;
            } else {
                System.out.println(temp.toString());
                temp = temp.next;
            }
        }
    }
 
    /**
     * 链表长度
     *
     * @return
     */
    public int length() {
        if (head.next == null) return 0;
        Node temp = this.head.next;
        int length = 0;
        while (temp != null) {
            length++;
            temp = temp.next;
        }
        return length;
    }
 
    /**
     * 获取倒数第index个node
     *
     * @param index 倒数下标
     * @return
     */
    public Node getNodeByLastIndex(int index) {
        int length = length();
        if (index > length || index < 1) {
            return null;
        }
        Node temp = this.head.next;
        for (int i = 0; i < length - index; i++) {
            temp = temp.next;
        }
        return temp;
    }
 
    /**
     * 反转链表
     */
    public void reverse() {
        //当前节点
        Node currentNode = this.head.next;
        //用于存储当前节点的下一个节点
        Node next;
        //创建个新头，相当于一条新链表
        Node reverseHead = new Node(0, "反转链表的头节点");
        while (currentNode != null) {
            next = currentNode.next;//存储当前节点的下一个节点，等会currentNode下一个节点会变化
 
            //这两句实现了把新节点插入到头节点的next域，也就是最后进来的，放在了最前面，也就实现了反转
            currentNode.next = reverseHead.next;//currentNode的下一节点指向反转链表的头节点的下一节点
            reverseHead.next = currentNode;//再反转链表的头节点的下一节点指向currentNode
 
            currentNode = next;//当前节点向后走
        }
        this.head.next = reverseHead.next;
    }
 
    /**
     * 添加有序链表，保证合并后还是有序
     */
    public void orderedAddAll(SingleLinkedList list) {
        Node tHead = this.head;
        Node oldNode = this.head.next;//被合并链表的第一个节点
        Node newNode = list.head.next;//合并链表的第一个节点
        while (oldNode != null || newNode != null) {
            //如果其中一个链表到尾了，直接把剩余的那个链表加进去
            if (oldNode == null) {
                tHead.next = newNode;
                newNode = newNode.next;
            } else if (newNode == null) {
                tHead.next = oldNode;
                oldNode = oldNode.next;
            } else if (oldNode.no <= newNode.no) {//如果小于等于则把被合并链表的节点添加进去
                tHead.next = oldNode;
                oldNode = oldNode.next;
            } else {
                tHead.next = newNode;
                newNode = newNode.next;
            }
            tHead=tHead.next;
        }
    }
 
    public static void main(String[] args) {
        SingleLinkedList list = new SingleLinkedList();
//        System.out.println("按末尾添加：");
//        Node node = new Node(1, "张三");
//        Node node2 = new Node(2, "李四");
//        Node node3 = new Node(3, "王五");
//        list.add(node);
//        list.add(node2);
//        list.add(node3);
        System.out.println("按no序号添加：");
        Node node = new Node(1, "张三");
        Node node3 = new Node(3, "王五");
        Node node2 = new Node(2, "李四");
        list.addByNo(node);
        list.addByNo(node3);
        list.addByNo(node2);
        list.list();
        list.deleteByNo(3);
        System.out.println("删除3后");
        list.list();
        System.out.println("删除33后");
        list.deleteByNo(33);
        list.list();
        System.out.println("更新2后");
        node2.name = "李小四";
        list.updateByNo(node2);
        list.list();
        System.out.println("获取no=1");
        System.out.println(list.getNodeByNo(1).toString());
        System.out.println("长度：" + list.length());
        System.out.println("倒数第一个：" + list.getNodeByLastIndex(1));
        System.out.println("倒数第二个：" + list.getNodeByLastIndex(2));
        System.out.println("倒数第三个：" + list.getNodeByLastIndex(3));
        System.out.println("添加几条数据：");
        list.add(new Node(10, "测试10"));
        list.add(new Node(20, "测试20"));
        list.add(new Node(30, "测试30"));
        list.list();
        System.out.println("反转链表：");
        list.reverse();
        list.list();
 
        //合并有序的
        SingleLinkedList list2 = new SingleLinkedList();
        list2.addByNo(new Node(1,"111"));
        list2.addByNo(new Node(3,"333"));
        list2.addByNo(new Node(7,"777"));
        list2.addByNo(new Node(9,"999"));
        list2.addByNo(new Node(5,"555"));
        SingleLinkedList list3 = new SingleLinkedList();
        list3.addByNo(new Node(2,"222"));
        list3.addByNo(new Node(4,"444"));
        list3.addByNo(new Node(0,"000"));
        list3.addByNo(new Node(6,"666"));
        list2.orderedAddAll(list3);
        System.out.println("合并有序链表list2和list3：");
        list2.list();
    }
 
}
 
/**
 * 节点类
 */
class Node {
    public int no;
    public String name;
    public Node next;
 
    public Node(int no, String name) {
        this.no = no;
        this.name = name;
    }
 
    @Override
    public String toString() {
        return "Node{" +
                "no=" + no +
                ", name='" + name + '\'' +
                '}';
    }
}

反转有一定难度，看着图比较好理解：