链表

基本概念

链表存储有序的元素集合，但不同于数组，链表中的元素在内存中并不是连续存储的，每个元素 由一个存储元素本身的节点和一个指向下一个元素的引用组成。

代码实现

// 节点类
class Node {
  constructor(val) {
    this.value = val;
    this.next = null;
  }
}


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

  // 向链表尾部添加一个新元素
  push(el) {
    let node = new Node(el);
    if (this.head) {
      let nextNode = this.head;
      while (nextNode.next != null) {
        nextNode = nextNode.next;
      }
      nextNode.next = node;
      this.length++;
    } else {
      this.head = node;
      this.length++;
    }
    return this.head;
  }

  // 向链表的特定位置插入元素
  insert(el, position) {
    let node = new Node(el);
    if (!this.head) {
      this.head = node;
    } else {
      if (position > this.length) {
        position = this.length;
      }
      let i = 1;
      let current = this.head;
      while (i < position) {
        current = current.next;
        i++;
      }
      node.next = current.next;
      current.next = node;
    }
    this.length++;
    return this.head;
  }

  // 获取指定位置处的元素
  getElementAt(index) {
    if (index >= this.length || index < 0) {
      return undefined;
    }
    let current = this.head;
    for (let i = 1; i <= index; i++) {
      current = current.next;
    }
    return current;
  }

  // 移除元素
  remove(index) {
    if (index < 0 || index >= this.length) {
      return this.head;
    }
    if (index === 0) {
      this.head = this.head.next;
      this.length--;
      return this.head;
    }
    let preNode = this.getElementAt(index - 1);
    let current = preNode.next;
    preNode.next = current.next;
    this.length--;
    return this.head;
  }

  // 返回元素在链表中的索引
  indexOf(val) {
    let current = this.head;
    for (let i = 0; i < this.length; i++) {
      if (current.value === val) {
        return i;
      }
      current = current.next;
    }
    return -1;
  }

  // 判断链表是否为空
  isEmpty() {
    return this.length === 0;
  }

  // 判断链表的长度
  size() {
    return this.length;
  }

  // toString方法
  toString() {
    let current = this.head;
    let stack = [];
    for (let i = 0; i < this.length; i++) {
      if(typeof current.value === 'object') {
        stack.push(`${JSON.stringify(current.value)}`); 
      } else {
        stack.push(`${current.value.toString()}`);
      }
      current = current.next;
    }
    return stack.join('->');
  }
}