我的查询助手方法中是否缺少基本情况？

问题描述

我有一个类 ParkingLot，我需要编写一个名为 enter() 的方法来检查停车场是否有空位。如果是，我输入汽车车牌号并将空缺计数减 1。

到目前为止，除了停车场已满外，一切正常，我需要将 vacantSpaces 调整为 0。

到目前为止我所拥有的：

class ParkingLot {
  constructor(capacity,rate) {
    this.spaces = new Array(capacity).fill('vacant');
    this.rate = rate;
    this.revenue = 0;
    this.queue = new Queue();
  }

  /**
   * Returns the number of vacant parking spaces
   * @returns {Number}
   *  the total number of spaces where the value is "vacant".
   */

  get vacantSpaces() {
    return this.spaces.reduce(
      (sum,space,index) => sum + (space === 'vacant' ? 1 : 0),0
    );
  }

  /**
   * As cars enter the parking lot,the license plate number is entered and the car is parked in the first vacant space.
   * If the lot is full,the car is added to the queue to be parked when a spot is available.
   *
   * @param licensePlateNumber
   *  the license plate number of the car entering
   */

  enter(licensePlateNumber) {
    const lot = new ParkingLot(licensePlateNumber);

    if (this.spaces.length > 1) {
      lot.enter(licensePlateNumber);
      this.spaces.shift();
    }
    if (this.spaces.length < 1) {
      lot.vacantSpaces = 0;
    }
  }
}

这是我的测试用例：

test("is zero when lot is full",() => {
      const parkingLot = new ParkingLot(2,1);

      parkingLot.enter("460-QRJ");
      parkingLot.enter("127-HLN");

      expect(parkingLot.vacantSpaces).toEqual(0);
    });

我不断得到：

Error: expect(received).toEqual(expected) // deep equality

Expected: 0
Received: 1

我是否遗漏了边缘情况，或者我当前的逻辑设置不正确？

解决方法

您的 enter 实现中的一些问题：

• 不要创建新的停车场。您只需要使用当前的parkingLot 实例(this)。
• 不要在 shift 数组上调用 this.spaces（想象一下所有会移动到邻近地点的汽车！）。而是找到免费位置（使用 indexOf）并在那里写下车牌号。
• 您不能将 this.vacantSpaces 更新为属性。它是一个吸气剂，而不是一个数字。无需更新任何内容，因为此 getter 将在调用时动态计算有多少空闲空间。

这是更正后的版本。我还添加了一个 leave 方法，并扩展了测试以便队列也被使用：

class ParkingLot {
  constructor(capacity,rate) {
    this.spaces = new Array(capacity).fill('vacant');
    this.rate = rate;
    this.revenue = 0;
    // Unless you have a very efficient Queue implementation,use a native 
    // Array,which already provides Queue operations
    this.queue = []; 
  }

  /**
   * Returns the number of vacant parking spaces
   * @returns {Number}
   *  the total number of spaces where the value is "vacant".
   */

  get vacantSpaces() {
    return this.spaces.reduce(
      (sum,space,index) => sum + (space === 'vacant' ? 1 : 0),0
    );
  }

  /**
   * As cars enter the parking lot,the license plate number is entered and the car is parked in the first vacant space.
   * If the lot is full,the car is added to the queue to be parked when a spot is available.
   *
   * @param licensePlateNumber
   *  the license plate number of the car entering
   */

  enter(licensePlateNumber) {
    // Don't create a new parkingLot. You want to use the current parkingLot instance (this)
    let space = this.spaces.indexOf('vacant');
    if (space >= 0) { // found a free spot
      this.spaces[space] = licensePlateNumber; // Overwrite 'vacant' with license place number
      // Don't shift the spaces array
    } else { // No free space
      this.queue.push(licensePlateNumber); // add to end of the queue
      // Don't write a value to this.vacantSpaces -- it already dynamically provides an updated value
    }
  }

  leave(licensePlateNumber) {
    let space = this.spaces.indexOf(licensePlateNumber);
    if (space >= 0) { // found its spot
      this.spaces[space] = 'vacant'; // Overwrite license place number with 'vacant'
      if (this.queue.length) { // There is a car waiting for a space
        this.enter(this.queue.shift()); // Attribute the first car in the queue to the new free space
      }
    }
  }
}

const parkingLot = new ParkingLot(2,1);

parkingLot.enter("460-QRJ");
parkingLot.enter("127-HLN");

console.log("vacant spaces: ",parkingLot.vacantSpaces);

parkingLot.enter("300-BEL");

console.log("vacant spaces: ",parkingLot.vacantSpaces);

parkingLot.leave("460-QRJ");

console.log("vacant spaces: ",parkingLot.vacantSpaces);

parkingLot.leave("127-HLN");

console.log("vacant spaces: ",parkingLot.vacantSpaces);