Java链表增删查改

import java.util.List;

/**
 * Created with IntelliJ IDEA.
 * Description: 链表
 * User: mac
 * Date: 2022-08-31
 * Time: 10:09
 */

//ListNode代表一个节点 - 存放在一个节点类中
class ListNode {
    public int val;
    public ListNode next;

    public ListNode(int val) {
        this.val = val;
    }
}
public class MyLinkedList {
    public ListNode head;//链表的头引用

    //打印链表
    public void display() {
        //this.head.next != null 会丢失一个数据
        ListNode cur = this.head;
        while (cur != null) {
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }

    //查找是否包含关键字k
    public boolean contains(int key) {
        ListNode cur = this.head;
        while (cur != null) {
            if (cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

    //得到单链表的长度
    public int size() {
        int count = 0;
        ListNode cur = this.head;
        while (cur != null) {
            count++;
            cur = cur.next;
        }
        return count;
    }

    //头插法
    public void addFirst(int data){
        //绑定位置的时候一定要先绑定后边
        ListNode node = new ListNode(data);
        node.next = this.head;
        this.head = node;
    }

    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if (this.head == null){//判空，否则就会造成引用异常this.head.next
            this.head = node;
        } else {
            ListNode cur = this.head;
            while (cur.next != null){
                cur = cur.next;
            }
            //cur.next = null;
            cur.next = node;
        }
    }

    public ListNode findindex(int index){//通过下表来移动指针
        ListNode cur = this.head;
        while (index - 1 != 0){
            cur = cur.next;
            index--;
        }
        return cur;
    }

    //任意位置插入，第一个数据节点为0号下标
    public void addIndex(int index, int data){
        if (index < 0 || index > size()){
            System.out.println("index位置不合法！");
            return;
        }
        if (index == 0){
            addFirst(data);
            return;
        }
        if (index == size()){
            addLast(data);
            return;
        }
        ListNode cur = findindex(index);
        ListNode node = new ListNode(data);
        node.next = cur.next;
        cur.next = node;
    }

    //删除第一次出现的关键字为key的节点
    public void remove(int key){
        if (this.head == null){
            System.out.println("单链表为空，不能删除！");
            return;
        }
        if (this.head.val == key){//判断头部是否为目标节点
            this.head = this.head.next;
            return;
        }
        ListNode cur = this.head;
        while (cur.next != null){
            if (cur.next.val == key){
                cur.next = cur.next.next;
                return;
            }
            cur = cur.next;
        }
        System.out.println("未找到该节点");
    }

    //删除所有值为key的节点
    public ListNode removeAllKey(int key){
        if (this.head == null) return null;

        ListNode prev = this.head;
        ListNode cur = this.head.next;

        while (cur != null){
            if (cur.val == key){
                prev.next = cur.next;
                cur = cur.next;
            } else{
                prev = cur;
                cur = cur.next;
            }
        }
        //最后处理头
        if (this.head.val == key){
            this.head = this.head.next;
        }
        return this.head;
    }

    //清空链表
    public void clear(){
        //this.head = null;//暴力解决 - 不推荐但没毛病
        while (this.head != null){
            ListNode curNext = this.head.next;
            this.head.next = null;
            this.head = curNext;
        }
    }

}