链表 js实现

链表的基本概念

链表是一种线性数据结构，由一系列节点组成，每个节点包含数据和指向下一个节点的指针（或引用）。与数组不同，链表在内存中是非连续存储的，插入和删除操作更高效。

单向链表的实现

以下是 JavaScript 中单向链表的实现代码，包含节点类和链表类的基本操作：

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

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

  // 在链表尾部添加节点
  append(data) {
    const newNode = new ListNode(data);
    if (!this.head) {
      this.head = newNode;
    } else {
      let current = this.head;
      while (current.next) {
        current = current.next;
      }
      current.next = newNode;
    }
    this.size++;
  }

  // 在指定位置插入节点
  insertAt(data, index) {
    if (index < 0 || index > this.size) return false;
    const newNode = new ListNode(data);
    if (index === 0) {
      newNode.next = this.head;
      this.head = newNode;
    } else {
      let current = this.head;
      let prev = null;
      let i = 0;
      while (i < index) {
        prev = current;
        current = current.next;
        i++;
      }
      newNode.next = current;
      prev.next = newNode;
    }
    this.size++;
    return true;
  }

  // 删除指定位置的节点
  removeAt(index) {
    if (index < 0 || index >= this.size) return null;
    let current = this.head;
    if (index === 0) {
      this.head = current.next;
    } else {
      let prev = null;
      let i = 0;
      while (i < index) {
        prev = current;
        current = current.next;
        i++;
      }
      prev.next = current.next;
    }
    this.size--;
    return current.data;
  }

  // 获取节点数据
  getData(index) {
    if (index < 0 || index >= this.size) return null;
    let current = this.head;
    let i = 0;
    while (i < index) {
      current = current.next;
      i++;
    }
    return current.data;
  }

  // 打印链表数据
  print() {
    let current = this.head;
    const result = [];
    while (current) {
      result.push(current.data);
      current = current.next;
    }
    console.log(result.join(" -> "));
  }
}

双向链表的实现

双向链表的节点包含指向前一个和后一个节点的指针，以下是实现代码：

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;
  }

  // 在尾部添加节点
  append(data) {
    const newNode = new DoublyListNode(data);
    if (!this.head) {
      this.head = newNode;
      this.tail = newNode;
    } else {
      newNode.prev = this.tail;
      this.tail.next = newNode;
      this.tail = newNode;
    }
    this.size++;
  }

  // 在头部添加节点
  prepend(data) {
    const newNode = new DoublyListNode(data);
    if (!this.head) {
      this.head = newNode;
      this.tail = newNode;
    } else {
      newNode.next = this.head;
      this.head.prev = newNode;
      this.head = newNode;
    }
    this.size++;
  }

  // 删除指定位置的节点
  removeAt(index) {
    if (index < 0 || index >= this.size) return null;
    let current = this.head;
    if (index === 0) {
      this.head = current.next;
      if (this.head) this.head.prev = null;
      else this.tail = null;
    } else if (index === this.size - 1) {
      current = this.tail;
      this.tail = current.prev;
      this.tail.next = null;
    } else {
      let i = 0;
      while (i < index) {
        current = current.next;
        i++;
      }
      current.prev.next = current.next;
      current.next.prev = current.prev;
    }
    this.size--;
    return current.data;
  }
}

链表的常见操作

• 查找节点：遍历链表直到找到目标数据或到达末尾。
• 反转链表：通过迭代或递归方式反转链表节点的指向。
• 检测环：使用快慢指针（Floyd 算法）判断链表是否有环。

应用场景

链表适合动态数据管理，如实现队列、栈、哈希表的链地址法等场景。其优势在于高效的插入和删除操作，但随机访问效率较低。