js 链表实现

链表基础概念

链表是一种线性数据结构，由一系列节点组成，每个节点包含数据部分和指向下一个节点的指针。与数组不同，链表的内存分配不要求连续，插入和删除操作效率更高。

单向链表实现

以下是单向链表的基本实现代码示例：

class ListNode {
  constructor(data) {
    this.data = data;
    this.next = null;
  }
}

class LinkedList {
  constructor() {
    this.head = null;
    this.size = 0;
  }

  // 添加节点到链表末尾
  add(data) {
    const node = new ListNode(data);
    if (!this.head) {
      this.head = node;
    } else {
      let current = this.head;
      while (current.next) {
        current = current.next;
      }
      current.next = node;
    }
    this.size++;
  }

  // 在指定位置插入节点
  insertAt(data, index) {
    if (index < 0 || index > this.size) return false;

    const node = new ListNode(data);
    if (index === 0) {
      node.next = this.head;
      this.head = node;
    } else {
      let current = this.head;
      let prev = null;
      let i = 0;

      while (i < index) {
        prev = current;
        current = current.next;
        i++;
      }
      node.next = current;
      prev.next = node;
    }
    this.size++;
    return true;
  }

  // 删除指定位置的节点
  removeFrom(index) {
    if (index < 0 || index >= this.size) return null;

    let removedNode;
    if (index === 0) {
      removedNode = this.head;
      this.head = this.head.next;
    } else {
      let current = this.head;
      let prev = null;
      let i = 0;

      while (i < index) {
        prev = current;
        current = current.next;
        i++;
      }
      removedNode = current;
      prev.next = current.next;
    }
    this.size--;
    return removedNode.data;
  }
}

双向链表实现

双向链表每个节点包含指向前后节点的指针：

class DoublyListNode {
  constructor(data) {
    this.data = data;
    this.prev = null;
    this.next = null;
  }
}

class DoublyLinkedList {
  constructor() {
    this.head = null;
    this.tail = null;
    this.size = 0;
  }

  // 添加到末尾
  add(data) {
    const node = new DoublyListNode(data);
    if (!this.head) {
      this.head = node;
      this.tail = node;
    } else {
      node.prev = this.tail;
      this.tail.next = node;
      this.tail = node;
    }
    this.size++;
  }
}

链表常用操作

打印链表内容：

printList() {
  let current = this.head;
  let str = "";
  while (current) {
    str += current.data + " -> ";
    current = current.next;
  }
  console.log(str + "null");
}

反转链表：

reverse() {
  let current = this.head;
  let prev = null;
  let next = null;

  while (current) {
    next = current.next;
    current.next = prev;
    prev = current;
    current = next;
  }
  this.head = prev;
}

性能特点

链表在插入和删除操作时时间复杂度为O(1)（已知位置情况下），而访问元素需要O(n)时间。适合频繁增删但随机访问较少的场景。