queue-dequeue

class Queue {

  constructor() {

    // Record the length of the queue , size 

    this.count = 0;

    // Record the first element of the queue 

    this.lowestCount = 0;

    // You can also use arrays here , But to get elements more efficiently , Use objects to store elements , 

    // and Stack Very similar , It's just that the principle of adding and removing elements is different 

    this.items = {};

  }

  // Is it an empty queue 

  isEmpty() {

    return this.count === 0;

  }
  // Number of queue elements 

  size() {

    return this.count - this.lowestCount;

  }

  // Clear queue 

  clear() {

    this.items = {};

    this.count = 0;

    this.lowestCount = 0;

  }

  // Add an item to the end of the queue 

  // The implementation method here and Stack The same way in the stack . take count As items The key in corresponds to the element as its value 

  enqueue(element) {

    this.items[this.count] = element;

    this.count++;

  }

  // Remove the first item , And return the removed element 

  dequeue() {

    if (this.isEmpty()) {

      return undefined;

    }

    const result = this.items[this.lowestCount];

    // Delete the first element 

    delete this.items[this.lowestCount];

    // The position of the first element added , Also move backward 

    this.lowestCount++;

    return result;

  }

  // Returns the first element in the queue , First added , It will also be the first element to be removed , The queue doesn't change , Just value 

  peek() {

    if (this.isEmpty()) {

      return undefined;

    }

    return this.items[this.lowestCount];

  }

  toString() {

    if (this.isEmpty()) {

      return '';

    }

    let queueString = this.items[this.lowestCount];

    for (let i = this.lowestCount + 1; i < this.count; i++) {

      queueString += `,${this.items[i]}`;

    }

    return queueString;

  }

}

class Deque {

  constructor() {

    this.count = 0;

    this.lowestCount = 0;
    this.items = {};

  }

  isEmpty() {

    return this.count === 0;

  }

  // Add elements to the front end 

  addFront(element) {

    if (this.isEmpty()) { // Empty queue 

      this.addBack(element);

    } else {

      this.lowestCount--;

      this.items[this.lowestCount] = element;

    }

  }
  // Add elements to the back end 

  addBack(element) {

    this.items[this.count] = element;

    this.count++;

  }
  // Remove... From the front end 

  removeFront() {

    if (this.isEmpty()) {

      return undefined;

    }

    const result = this.items[this.lowestCount];

    // Delete the first element 

    delete this.items[this.lowestCount];

    // The position of the first element added , Also move backward 

    this.lowestCount++;

    return result;

  }
  // Remove... From the back end 

  removeBack() {

    if (this.isEmpty()) {

      return undefined;

    }

    this.count--;

    const result = this.items[this.count];

    delete this.items[this.count];

    return result;

  }
  // Return the front most element 

  peekFront() {

    if (this.isEmpty()) {

      return undefined;

    }

    return this.items[this.lowestCount];

  }
  // Return the last element 

  peekBack() {

    if (this.isEmpty()) {

      return undefined;

    }

    return this.items[this.count - 1];

  }

}

const dequeue = new Deque();
dequeue.addFront(1);
dequeue.addBack(2);
dequeue.addFront(5);
dequeue.addBack('x');
dequeue.removeBack();
console.log(dequeue);