JavaScript Interview Question: Create a Queue using Stacks

queue-stack.js

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Create a Queue implementation using two stacks. Do not use an
 * array inside the Queue class. Queue should implement add() and
 * remove().
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

class Stack {
  constructor() {
    this.data = [];
  }
  
  push(record) {
    this.data.push(record);
  }
  
  pop() {
    return this.data.pop();
  }
  
  peek() {
    return this.data[this.data.length - 1];
  }
}

class Queue {
  constructor() {
    this.stackA = new Stack();
    this.stackB = new Stack();
  }
  
  add(record) {
    this.stackA.push(record);
  }
  
  remove() {
    while (this.stackA.peek()) {
      this.stackB.push(this.stackA.pop());
    }
    
    const returnValue = this.stackB.pop();
    
    while (this.stackB.peek()) {
      this.stackA.push(this.stackB.pop());
    }
    
    return returnValue;
  }
}

// Test it
(() => {
  let queue = new Queue();
  queue.add('A');
  queue.add('B');
  queue.add('C');
  
  console.log('remove 1', queue.remove());
  console.log('remove 2', queue.remove());
  console.log('remove 3', queue.remove());
})();