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    【Java数据结构】—— 双向链表及带傀儡节点双向链表的实现

    2021-12-21 00:13

    引言

    在之前的博文中，我简单的向大家分享了一些链表相关的知识及一些面试题，如果感兴趣的老铁可以去瞧瞧！今天给大家带来双向链表以及带傀儡节点的双向链表的实现。认真看，每一步都有具体的来由和理解，希望对大家有所帮助！

    详细步骤解析咋们边看代码边学习！

    双向链表的实现

    class ListNode{
    public int val;//数值域
    public ListNode prev;
    public ListNode next;
    public ListNode(int val) {
        this.val = val;
    }
}
public class DoubleLinkedList {
    public ListNode head;//指向双链表的头节点
    public ListNode last;//指向双链表尾巴节点
    //打印链表--和打印单链表的方式一样
    public void display(){
        ListNode cur = this.head;
        while (cur!=null) {
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }
    //得到单链表的长度
    public int size(){
        int count = 0;//记录节点个数
        ListNode cur = this.head;
        while (cur!=null) {
            count++;
            cur = cur.next;
        }
        return count;
    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        ListNode cur = this.head;
        while (cur!=null) {
            if(cur.val == key) {//如果cur.val等于key返回真
                return true;
            }//否则继续往下走
            cur = cur.next;
        }
        return false;
    }
    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);//new了个插入节点
        if(head == null) {//如果插入时链表为空则，头和尾都指向新节点node
            this.head = node;
            this.last = node;
        }else {
            node.next = head;
            head.prev = node;
            this.head = node;
        }
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(this.head == null) {
            this.head = node;
            this.last = node;
        }else {
           this.last.next = node;
           node.prev = last;
           this.last = node;
        }
    }
    //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");
        }
        if(index == 0) {
            addFirst(data);
        }
        if(index==size()){
            addLast(data);
        }
        ListNode cur = searchIndex(index);
        node.next =  cur.prev.next;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }
    public ListNode searchIndex(int index) {
        ListNode cur = this.head;//创建个方法找到插入时cur的位置
        while (index != 0) {
            cur = cur.next;
            index--;
        }
        return cur;
    }

    //删除第一次出现关键字为key的节点
    //单链表中删除第一次出现的关键字需要找到关键字前驱
    //双链表只需要直接找到这个节点
    public void remove(int key){
        ListNode cur = this.head;
        while (cur!=null) {
            if(cur.val == key) {//这里分两种情况
                if(cur == head) {//1.cur等于头结点
                    head = head.next;
                    head.prev = null;//手动置为空

                }else {//2.cur不等于头结点
                    cur.prev.next = cur.next;
                    if(cur.next!=null) {
                        //中间位置
                        cur.next.prev = cur.prev;
                    }else {//尾巴位置
                         last = last.prev;
                    }
                }
                return;
            }else {
                cur = cur.next;
            }
        }

    }

    //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) {
                        head.prev = null;
                    } else {
                        last = null;
                    }
                } else {
                    cur.prev.next = cur.next;
                    if (cur.next != null) {
                        //中间位置
                        cur.next.prev = cur.prev;
                    } else {
                        last = last.prev;
                    }
                }
                //return;
            }
            cur = cur.next;
        }
    }


    public void clear(){
        while (head!=null) {
            ListNode curNext = head.next;
            head.next = null;
            head.prev = null;
            head = curNext;
        }
        last = null;
    }
}

双向链表增删添改的实现

    public class TestDemo {
    public static void main(String[] args) {
        DoubleLinkedList doubleLinkedList = new DoubleLinkedList();
        doubleLinkedList.addLast(12);
        doubleLinkedList.addLast(13);
        doubleLinkedList.addLast(14);
        doubleLinkedList.addLast(15);
        doubleLinkedList.addLast(16);
        doubleLinkedList.display();
        System.out.println("=================");
        doubleLinkedList.addIndex(3,99);
        doubleLinkedList.display();
    }
}

带傀儡节点的双向链表的实现


    class ListNode{
    public int val;
    public ListNode next;
    public ListNode prev;
    public ListNode(int val) {
        this.val = val;
    }
}
public class DoubleLinkedList {//带傀儡节点的双链表
    public ListNode dummyHead;//虚拟节点
    public ListNode last;//尾节点

    public DoubleLinkedList() {
        this.dummyHead = new ListNode(-1);//傀儡节点
    }

    //打印单链表
    public void display() {
        ListNode cur = this.dummyHead.next;
        //引用cur代替head，head等于傀儡节点下一个节点
        while (cur != null) {
            System.out.print(cur.val + " ");
            cur = cur.next;
        }
        System.out.println();
    }

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

    //头插法
    public void addFirst(int data) {
        ListNode node = new ListNode(data);
        //第一次插入一个节点都没有的情况
        if (this.dummyHead.next == null) {
            node.prev = dummyHead;
            this.dummyHead.next = node;
            this.last = node;
            return;
        } else {
            //新插入的节点和他前后节点连接
            node.next = this.dummyHead.next;
            node.prev = this.dummyHead;
            this.dummyHead.next.prev = node;
            this.dummyHead.next = node;
        }
    }

    //尾插法
    public void addLast(int data) {
        ListNode node = new ListNode(-1);
        //判断头节点是否为空
        if (this.dummyHead.next == null && this.last.next == null) {
            this.dummyHead.next = node;
            node.prev = this.dummyHead;
            this.last = node;
            return;
        } else {
            this.last.next = node;
            node.prev = last;
            this.last = node;
        }
    }

    //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;
        }else {
            if(index == 0) {
                addFirst(data);
            }
            if(index == size()) {
                addLast(data);
            }else {
                //中间位置的时候
                ListNode cur = searchIndex(index);
                node.next = cur;
                cur.prev.next = node;
                node.prev = cur.prev;
                cur.prev = node;
            }
        }
    }
    //创建个方法找到cur的位置
    public ListNode searchIndex(int index) {
        //先找到cur的位置
        ListNode cur = this.dummyHead.next;
        while (index!=0) {
            cur = cur.next;
            index--;
        }
        return cur;
    }

        //查找是否包含关键字key是否在单链表当中
        public boolean contains(int key){
        ListNode cur = this.dummyHead.next;
        while (cur!=null) {
            if(cur.val == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
        //删除第一次出现关键字为key的节点
        //单链表中删除第一次出现的关键字需要找到关键字前驱
        //双链表只需要直接找到这个节点
        public void remove(int key){
        ListNode cur = this.dummyHead.next;
        if(cur.val == key){//有两种情况 cur=head或者cur不等于head
            if(cur == this.dummyHead.next) {//cur==head时
                this.dummyHead.next = this.dummyHead.next.next;
                this.dummyHead.next.next.prev = null;
            }else {//cur不等于head又有两种情况
                //1.cur在中间位置2.cur在最后的位置
                cur.prev.next = cur.next;
                //判断是不是最后一个节点
                //要删除的节点不是最后一个节点
                if(cur.next!=null){
                    cur.next.prev = cur.prev;
                }else {
                    this.last = cur.prev;
                }
            }
            return;
        }else {
            cur = cur.next;
        }

    }
        //删除所有值为key的节点
        public void removeAllKey(int key){
        ListNode cur = this.dummyHead.next;
        while (cur!=null) {
            if(cur.val == key){
                if(cur == this.dummyHead.next) {
                    this.dummyHead.next = this.dummyHead.next.next;
                    this.dummyHead.next.prev = null;
                }else {
                    cur.prev.next = cur.next;
                    //判断如果是最后一个节点
                    if(cur.next == null) {
                        this.last = cur.prev;
                    }else {
                        cur.next.prev = cur.prev;
                    }
                }
            }
            cur = cur.next;
        }
    }

        public void clear(){
        ListNode cur = this.dummyHead.next;
        ListNode curNext = cur.next;
        while (cur!=null) {
            cur.prev = null;
            cur.next = null;
            cur = curNext;
        }
        this.dummyHead = null;
        this.last = null;
    }
}
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