java：实现双向链表-爱代码爱编程

class ListNode{
    public int val;
    public ListNode prev;
    public ListNode next;

    public ListNode(int val){  //构造方法和类名是一样的，只对val初始化，因为当又一个节点的时候，不知道前一个后一个是谁
        this.val = val;
    }
}

public class MyDoubleList {
    public ListNode head;  //ListNode--是个类型 //head--指向头节点
    public ListNode last;  //last--指向尾巴节点


    //一、打印双向链表
    public void display(){
        ListNode cur = this.head;
        while (cur != null){
            System.out.print(cur.val+" ");
            cur = cur.next;
        }
        System.out.println( );
    }



    //二、得到双链表的长度
    public int size(){
        ListNode cur = this.head;
        int count = 0;
        while (cur != null){
            count++;
            cur = cur.next;
        }
        return count;
    }



    //三、查找双链表是否包含关键字key
    public boolean contains(int key){
        ListNode cur = this.head;
        while (cur != null){
            if (cur.val == key){
                return true;
            }
            cur = cur.next;
        }
        return false;
    }



    //四、头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if (head == null){
            this.head = node;
            this.last = node;
        }else {
            node.next = this.head;
            this.head.prev = node;
            this.head = node;
        }
    }



    //五、尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if (head == null){
            this.head = node;
            this.last = node;
        }else {
            last.next = node;
            node.prev = last;
            this.last = node;
        }
    }



    //六、删除第一次出现关键字为key的节点
    public void remove(int key) {
        ListNode cur = this.head;
        while (cur != null) {
            if (cur.val == key) {
                if (cur == head) {
                    head = head.next;
                    if (head.next != null){  //考虑到一个节点的情况
                        head.prev = null;
                    }else {  //head==null
                        last = null;
                    }
                } else {
                    cur.prev.next = cur.next;
                    if (cur.next != null) { //说明cur在中间位置
                        cur.next.prev = cur.prev;
                    } else {
                        last = last.prev;
                    }
                }
                return;
            }
            cur = cur.next;
        }
    }




    //七、删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = this.head;
        while (cur != null) {
            if (cur.val == key) {
                if (cur == head) {
                    head = head.next;
                    if (head != null){  //考虑到一个节点的情况
                        head.prev = null;
                    }else {  //head==null
                        last = null;
                    }
                } else {
                    cur.prev.next = cur.next;
                    if (cur.next != null) { //说明cur在中间位置
                        cur.next.prev = cur.prev;
                    } else {
                        last = last.prev;
                    }
                }
            }
            cur = cur.next;
        }
    }




    public ListNode searchIndex(int index){
        ListNode cur = this.head;
        while (index != 0){
            cur = cur.next;
            index--;
        }
        return cur;
    }
     //八、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){
        ListNode node = new ListNode(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 = searchIndex(index);
        node.next = cur.prev.next;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }



    //九、清空双链表
    public void clear(){
        while (head != null){
            ListNode curNext = head.next;
            head.next = null;
            head.prev = null;
            head = curNext;
        }
        last = null;
    }
}