Java实现双链表的示例代码

目录

• 一、双向链表是什么
• 二、具体方法实现
• 定义结点
• 下标访问异常
• 获取链表长度
• 打印链表
• 清空链表
• 头插法
• 尾插法
• 指定位置插入
• 查找元素
• 删除第一次出现的关键字
• 删除所有值为key的节点
• 三、完整代码

一、双向链表是什么

双向链表也叫双链表，是链表的一种，它的每个数据结点中都有两个指针，分别指向直接后继和直接前驱。所以，从双向链表中的任意一个结点开始，都可以很方便地访问它的前驱结点和后继结点。一般我们都构造双向循环链表。

LinkedList底层就是一个双向链表，我们来实现一个双向链表。

这里多一个尾指针，方便我们对尾插操作从O(n)降到O(1).每个结点多了前驱结点，方便我们对链表进行操作。

二、具体方法实现

定义结点

class ListNode {
        int value;
        ListNode next;
        ListNode prev;

        public ListNode(int value) {
            this.value = value;
        }
    }

下标访问异常

public class IndexWrongException extends RuntimeException{
    public IndexWrongException() {
    }

    public IndexWrongException(String message) {
        super(message);
    }
}

获取链表长度

class ListNode {
        int value;
        ListNode next;
        ListNode prev;

        public ListNode(int value) {
            this.value = value;
        }
    }

打印链表

class ListNode {
        int value;
        ListNode next;
        ListNode prev;

        public ListNode(int value) {
            this.value = value;
        }
    }

清空链表

public void clear(){
        if(this.head == null) {
            return;
        }
        ListNode cur = this.head;
        while(cur != null) {
            ListNode curNext = cur.next;
            cur.prev = null;
            cur.next = null;
            cur = curNext;
        }
        head = null;
        tail = null;
    }

头插法

public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            this.head = node;
            this.tail = node;
            return;
        }
        node.next = this.head;
        this.head.prev = node;
        this.head = node;
    }

尾插法

public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            this.head = node;
            this.tail = node;
            return;
        }
        tail.next = node;
        node.prev = tail;
        tail = node;
    }

指定位置插入

public void addIndex(int index,int data) throws IndexWrongException{
        if(index < 0 || index > size()) {
            throw new IndexWrongException("输入下标不合法");
        }
        ListNode node = new ListNode(data);
        if(index == 0) {
            addFirst(data);
            return;
        }
        if(index == size()) {
            addLast(data);
            return;
        }
        ListNode cur = this.head;
        while(index != 0) {
            cur = cur.next;
            index--;
        }
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }

查找元素

public boolean contains(int key){
        if(head == null) {
            return false;
        }
        ListNode cur = this.head;
        while(cur != null) {
            if(cur.value == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }

删除第一次出现的关键字

public void remove(int key){
        ListNode cur = head;
        while(cur != head) {
            if(cur.value == key) {
                if(cur == head) {
                    head = head.next;
                    if(head.next != null) {
                        head.prev = null;
                    }else {
                        tail = null;
                    }
                }else {
                    cur.prev.next = cur.next;
                    if(cur.next != null) {
                        cur.next.prev = cur.prev;
                    }else {
                        tail = cur.prev;
                        tail.next = null;
                        }
                    }
                return;
                }
            cur = cur.next;
            }
        }

删除所有值为key的节点

public void removeAllKey(int key){
        ListNode cur = head;
        while(cur != head) {
            if(cur.value == key) {
                if(cur == head) {
                    head = head.next;
                    if(head.next != null) {
                        head.prev = null;
                    }else {
                        tail = null;
                    }
                }else {
                    cur.prev.next = cur.next;
                    if(cur.next != null) {
                        cur.next.prev = cur.prev;
                    }else {
                        tail = cur.prev;
                        tail.next = null;
                    }
                }
            }
            cur = cur.next;
        }
    }

三、完整代码

public class LinkedList {
    static class ListNode {
        int value;
        ListNode next;
        ListNode prev;

        public ListNode(int value) {
            this.value = value;
        }
    }
    ListNode head;
    ListNode tail;
    //头插法
    public void addFirst(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            this.head = node;
            this.tail = node;
            return;
        }
        node.next = this.head;
        this.head.prev = node;
        this.head = node;
    }
    //尾插法
    public void addLast(int data){
        ListNode node = new ListNode(data);
        if(head == null) {
            this.head = node;
            this.tail = node;
            return;
        }
        tail.next = node;
        node.prev = tail;
        tail = 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) throws IndexWrongException{
        if(index < 0 || index > size()) {
            throw new IndexWrongException("输入下标不合法");
        }
        ListNode node = new ListNode(data);
        if(index == 0) {
            addFirst(data);
            return;
        }
        if(index == size()) {
            addLast(data);
            return;
        }
        ListNode cur = this.head;
        while(index != 0) {
            cur = cur.next;
            index--;
        }
        node.next = cur;
        cur.prev.next = node;
        node.prev = cur.prev;
        cur.prev = node;
    }
    //查找是否包含关键字key是否在单链表当中
    public boolean contains(int key){
        if(head == null) {
            return false;
        }
        ListNode cur = this.head;
        while(cur != null) {
            if(cur.value == key) {
                return true;
            }
            cur = cur.next;
        }
        return false;
    }
    //删除第一次出现关键字为key的节点
    public void remove(int key){
        ListNode cur = head;
        while(cur != head) {
            if(cur.value == key) {
                if(cur == head) {
                    head = head.next;
                    if(head.next != null) {
                        head.prev = null;
                    }else {
                        tail = null;
                    }
                }else {
                    cur.prev.next = cur.next;
                    if(cur.next != null) {
                        cur.next.prev = cur.prev;
                    }else {
                        tail = cur.prev;
                        tail.next = null;
                        }
                    }
                return;
                }
            cur = cur.next;
            }
        }
    //删除所有值为key的节点
    public void removeAllKey(int key){
        ListNode cur = head;
        while(cur != head) {
            if(cur.value == key) {
                if(cur == head) {
                    head = head.next;
                    if(head.next != null) {
                        head.prev = null;
                    }else {
                        tail = null;
                    }
                }else {
                    cur.prev.next = cur.next;
                    if(cur.next != null) {
                        cur.next.prev = cur.prev;
                    }else {
                        tail = cur.prev;
                        tail.next = null;
                    }
                }
            }
            cur = cur.next;
        }
    }
    //得到单链表的长度
    public int size(){
        ListNode cur = head;
        int count = 0;
        while(cur != null) {
            cur = cur.next;
            count++;
        }
        return count;
    }
    public void display(){
        ListNode cur = head;
        while (cur != null) {
            System.out.print(cur.value+" ");
            cur = cur.next;
        }
        System.out.println();
    }
    public void clear(){
        if(this.head == null) {
            return;
        }
        ListNode cur = this.head;
        while(cur != null) {
            ListNode curNext = cur.next;
            cur.prev = null;
            cur.next = null;
            cur = curNext;
        }
        head = null;
        tail = null;
    }
}

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