翻转单链表

结果：

//翻转链表
    public static HeroNode reverseLinkedList(HeroNode head){
        if (head.next == null) {
            System.out.println("链表为空无法翻转");
            return null;
        }
        //prev
        HeroNode prev = null;
        //cur
        HeroNode cur = head.next;
        //next
        HeroNode next = null;
        while (cur != null) {
            next = cur.next;
            cur.next = prev;
            prev=cur;//当cur为空时，prev就为最后一个结点
            cur=next;
        }
        head.next=prev;
        return head;
    }

完整测试代码：

package com.nan;

/**
 * @author klr
 * @create 2020-07-01-23:07
 */
public class SingleLinkedListDemo {

    public static void main(String[] args) {
        HeroNode hero4 = new HeroNode(4, "林冲", "豹子头");
        HeroNode hero1 = new HeroNode(1, "宋江", "及时雨");
        HeroNode hero2 = new HeroNode(2, "卢俊义", "玉麒麟");
        HeroNode hero3 = new HeroNode(3, "吴用", "智多星");

        SingleLinkedList singleLinkedList = new SingleLinkedList();
        singleLinkedList.add(hero1);
        singleLinkedList.add(hero2);
        singleLinkedList.add(hero3);
        singleLinkedList.add(hero4);

        System.out.println("修改前");
        singleLinkedList.list();
        singleLinkedList.update(new HeroNode(1,"小宋","及时雨"));
        System.out.println("修改后");
        singleLinkedList.list();
        System.out.println("删除结点2");
        singleLinkedList.delete(2);
        singleLinkedList.list();
        System.out.println("查找链表的第K个结点,从1开始");
        System.out.println(singleLinkedList.getKNode(singleLinkedList.getHead(), 3));
        System.out.println("翻转链表");
        SingleLinkedList.reverseLinkedList(singleLinkedList.getHead());
        singleLinkedList.list();

    }
}

class SingleLinkedList{

    //头结点，不能动，不存放具体的数据
    private HeroNode head = new HeroNode(0,"","");

    //翻转链表
    public static HeroNode reverseLinkedList(HeroNode head){
        if (head.next == null) {
            System.out.println("链表为空无法翻转");
            return null;
        }
        //prev
        HeroNode prev = null;
        //cur
        HeroNode cur = head.next;
        //next
        HeroNode next = null;
        while (cur != null) {
            next = cur.next;
            cur.next = prev;
            prev=cur;//当cur为空时，prev就为最后一个结点
            cur=next;
        }
        head.next=prev;
        return head;
    }

    public HeroNode getHead() {
        return head;
    }

    //求链表的长度
    public static int getLength(HeroNode head){
        if (head.next == null) {
            return 0;
        }
        HeroNode cur = head.next;
        int count=0;
        while (cur != null) {
            count++;
            cur = cur.next;
        }
        return count;
    }

    //查找单链表的倒数第K个结点
    //参数：head和k
    public HeroNode getKNode(HeroNode head, int k) {
        if (head.next == null) {
            return null;
        }
        if (getLength(head) < k||k<=0) {
            System.out.println(("参数小于1或者大于链表长度，无法查找"));
            return null;
        }
        int position = getLength(head) - k + 1;//也可以去掉+1，后面的position>=0
        HeroNode temp = head;
        while (position >= 1) {
            position--;
            temp = temp.next;
        }
        return temp;
    }

    //找到当前链表的最后结点
    //将最后这个结点的next指向新的结点
    public void add(HeroNode heroNode){
        //因为head结点不动，我们需要定义一个零时结点
        HeroNode temp = head;
        //判断英雄是否重复
        boolean flag = false;
        while (true) {
            if (temp.next == null) {
                break;
            }
            if (temp.next.number > heroNode.number) {
                break;
            } else if (temp.next.number == heroNode.number) {
                flag = true;//说明该英雄存在，无法添加
                break;
            }
            temp = temp.next;
        }
        if (flag) {
            System.out.printf("英雄%d存在，无法添加\n",heroNode.number);
            return;
        }
        heroNode.next=temp.next;
        temp.next=heroNode;
//        //遍历这个链表，找到最后
//        while (true) {
//            //列表为空，直接添加
//            if (temp.next == null) {
//                temp.next = heroNode;
//                break;
//            }
//            //比较大小，直接插入
//            if (temp.number <= heroNode.number && heroNode.number <= temp.next.number) {
//                heroNode.next = temp.next;
//                temp.next = heroNode;
//                break;
//            }
//            //如果没有找到，就继续找
//            temp = temp.next;
//        }
    }

    //根据id修改结点
    public void update(HeroNode newHeroNode) {
        if (head.next == null) {
            System.out.println("链表为空，无法修改");
            return;
        }
        HeroNode temp = head.next;
        boolean flag = false;
        while (true) {
            if (temp == null) {
                break;//已经遍历完链表
            }
            if (temp.number == newHeroNode.number) {
                flag=true;
                break;
            }
            temp=temp.next;
        }
        if (flag) {
            temp.name = newHeroNode.name;
            temp.nickName = newHeroNode.nickName;
        }
        else {
            System.out.printf("未找到编号为%d的英雄\n",newHeroNode.number);
        }
    }

    //删除结点
    public void delete(int number) {
        HeroNode temp = head;
        if (temp.next == null) {
            System.out.println("该链表为空");
            return;
        }
        boolean flag = false;
        while (true) {
            if (temp.next == null) {
                break;//遍历完链表
            }
            if (temp.next.number == number) {
                flag =  true;//找到结点
                break;
            }
            temp=temp.next;
        }
        if (flag) {
            temp.next=temp.next.next;
        }
        else {
            System.out.printf("编号%d的英雄不存在",number);
        }
    }

    //遍历
    public void list(){
        //判断链表是否为空
        if (head.next == null) {
            System.out.println("链表为空");
            return;
        }
        //因为head不能动
        HeroNode temp = head.next;
        while (true) {
            //判断是否到链表最后
            if (temp == null) {
                break;
            }
            //输出结点信息
            System.out.println(temp);
            //将temp后移
            temp = temp.next;
        }
    }
}

class HeroNode {
    public int number;//排名
    public String name;//姓名
    public String nickName;//绰号
    public HeroNode next;//指针

    public HeroNode(int number, String name, String nickName) {
        this.number = number;
        this.name = name;
        this.nickName = nickName;
    }

    @Override
    public String toString() {
        return "HeroNode{" +
                "number=" + number +
                ", name='" + name + '\'' +
                ", nickName='" + nickName +
                '}';
    }
}