队列

队列基本操作有两种: 向队列的后端位置添加实体，称为入队，并从队列的前端位置移除实体，称为出队。跟超市排队差不多吧，前面的结算好，就出队，后面刚刚来的入队。

队列中元素先进先出 FIFO (first in, first out)的示意

 

复杂度

时间复杂度

获取：O(n)

查询：O(n)

插入：O(1)

删除：O(1)

空间复杂度

O(n)

 

Queue:队列是在链表的基础上进行操作的。

import LinkedList from '../linked-list/LinkedList';

export default class Queue {//队列类，队列其实就是一端添加，一端删除的链表
  constructor() {
    // We're going to implement Queue based on LinkedList since the two
    // structures are quite similar. Namely, they both operate mostly on
    // the elements at the beginning and the end. Compare enqueue/dequeue
    // operations of Queue with append/deleteHead operations of LinkedList.
    this.linkedList = new LinkedList();//linkedList属性是一个链表对象
  }

  /**
   * @return {boolean}
   */
  isEmpty() {//返回真假值，队列是否是空的
    return !this.linkedList.head;
  }

  /**
   * Read the element at the front of the queue without removing it.
   * @return {*}
   */
  peek() {//读取队列的头节点
    if (!this.linkedList.head) {
      return null;
    }

    return this.linkedList.head.value;
  }

  /**
   * Add a new element to the end of the queue (the tail of the linked list).
   * This element will be processed after all elements ahead of it.
   * @param {*} value
   */
  enqueue(value) {//入队，在队列的结尾加入新值
    this.linkedList.append(value);
  }

  /**
   * Remove the element at the front of the queue (the head of the linked list).
   * If the queue is empty, return null.
   * @return {*}
   */
  dequeue() {//出队，在队列的开头删除值，返回出队的值
    const removedHead = this.linkedList.deleteHead();
    return removedHead ? removedHead.value : null;
  }

  /**
   * @param [callback]
   * @return {string}
   */
  toString(callback) {//返回队列的字符串值的数组的字符串
    // Return string representation of the queue's linked list.
    return this.linkedList.toString(callback);
  }
}

note:

1.进队相当于尾插法，出对相当于头删法。

2.队列非空,队列方法非空。

it('should create empty queue', () => {
    const queue = new Queue();
    expect(queue).not.toBeNull();
    expect(queue.linkedList).not.toBeNull();
  });

Received: {"linkedList": {"compare": {"compare": [Function defaultCompareFunction]}, "head": null, "tail": null}}

import LinkedList from '../linked-list/LinkedList';
export default class Queue {//队列类，队列其实就是一端添加，一端删除的链表  constructor() {    // We're going to implement Queue based on LinkedList since the two    // structures are quite similar. Namely, they both operate mostly on    // the elements at the beginning and the end. Compare enqueue/dequeue    // operations of Queue with append/deleteHead operations of LinkedList.    this.linkedList = new LinkedList();//linkedList属性是一个链表对象  }
  /**   * @return {boolean}   */  isEmpty() {//返回真假值，队列是否是空的    return !this.linkedList.head;  }
  /**   * Read the element at the front of the queue without removing it.   * @return {*}   */  peek() {//读取队列的头节点    if (!this.linkedList.head) {      return null;    }
    return this.linkedList.head.value;  }
  /**   * Add a new element to the end of the queue (the tail of the linked list).   * This element will be processed after all elements ahead of it.   * @param {*} value   */  enqueue(value) {//入队，在队列的结尾加入新值    this.linkedList.append(value);  }
  /**   * Remove the element at the front of the queue (the head of the linked list).   * If the queue is empty, return null.   * @return {*}   */  dequeue() {//出队，在队列的开头删除值，返回出队的值    const removedHead = this.linkedList.deleteHead();    return removedHead ? removedHead.value : null;  }
  /**   * @param [callback]   * @return {string}   */  toString(callback) {//返回队列的字符串值的数组的字符串    // Return string representation of the queue's linked list.    return this.linkedList.toString(callback);  }}