链表是什么？JS中怎样实现链表结构

class Node {
    constructor(data) {
        this.data = data; // 节点存储的数据
        this.next = null; // 指向下一个节点的引用，初始为null
    }
}

class LinkedList {
    constructor() {
        this.head = null; // 链表的头部，初始为空
        this.size = 0;    // 链表中节点的数量
    }

    // 添加节点到链表末尾
    append(data) {
        const newNode = new Node(data);
        if (!this.head) {
            // 如果链表为空，新节点就是头部
            this.head = newNode;
        } else {
            // 遍历到链表末尾，将新节点添加到最后
            let current = this.head;
            while (current.next) {
                current = current.next;
            }
            current.next = newNode;
        }
        this.size++;
    }

    // 在链表头部添加节点
    prepend(data) {
        const newNode = new Node(data);
        newNode.next = this.head; // 新节点的next指向原头部
        this.head = newNode;      // 新节点成为新的头部
        this.size++;
    }

    // 在指定位置插入节点
    insertAt(data, index) {
        if (index < 0 || index > this.size) {
            console.error("插入位置无效");
            return;
        }
        if (index === 0) {
            this.prepend(data);
            return;
        }

        const newNode = new Node(data);
        let current = this.head;
        let previous;
        let count = 0;

        while (count < index) {
            previous = current;
            current = current.next;
            count++;
        }

        newNode.next = current;
        previous.next = newNode;
        this.size++;
    }

    // 查找节点（按数据）
    find(data) {
        let current = this.head;
        while (current) {
            if (current.data === data) {
                return current; // 找到并返回节点
            }
            current = current.next;
        }
        return null; // 未找到
    }

    // 删除指定数据的节点
    delete(data) {
        if (!this.head) {
            return null;
        }

        if (this.head.data === data) {
            this.head = this.head.next; // 如果是头部，直接移动头部指针
            this.size--;
            return;
        }

        let current = this.head;
        let previous = null;
        while (current && current.data !== data) {
            previous = current;
            current = current.next;
        }

        if (current) {
            previous.next = current.next; // 跳过当前节点，实现删除
            this.size--;
        } else {
            console.warn(`未找到数据为 ${data} 的节点`);
        }
    }

    // 遍历链表并打印所有节点数据
    printList() {
        let current = this.head;
        let listStr = "";
        while (current) {
            listStr += current.data + " -> ";
            current = current.next;
        }
        listStr += "null";
        console.log(listStr);
    }
}

// 示例用法
const myList = new LinkedList();
myList.append(10);
myList.append(20);
myList.prepend(5);
myList.insertAt(15, 2); // 5 -> 10 -> 15 -> 20 -> null
myList.printList(); // 输出: 5 -> 10 -> 15 -> 20 -> null

myList.delete(10);
myList.printList(); // 输出: 5 -> 15 -> 20 -> null

console.log("查找 15:", myList.find(15)?.data); // 输出: 查找 15: 15

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