JavaScript Interview Question: Queue

queue.js

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Solve some arbitrary problem using a queue.
 * The interviewer has asked to provide a solution to a problem
 * using a Queue as the data structure. Using the native Array
 * in JavaScript with restricted access to its full list of methods
 * is one possible solution.
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

//Queues implement the FIFO method. First in, first out.
class Queue {
  constructor() {
    this.queue = [];
  }
  
  add(record) {
    // Use Array#unshift to add record at the beginning of the array.
    this.queue.unshift(record);
  }
  
  remove() {
    //Remove and return the last element in the array.
    return this.queue.pop();
  }
}

//Test it.
(() => {
  let queue = new Queue();

  queue.add(1);
  queue.add(2);
  queue.add(3);
  
  let result = queue.remove();
  
  console.log(result);
})();

weave-queue.js

/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Weave, or merge the results of two queues together into a 
 * single queue.
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

class Queue {
  constructor() {
    this.queue = [];
  }
  
  add(record) {
    this.queue.unshift(record);
  }
  
  remove() {
    return this.queue.pop();
  }

  peek() {
    return this.queue[this.queue.length - 1];
  }
}


// Test it.
(() => {
  let q1 = new Queue();
  let q2 = new Queue();
  
  // Populate Queue 1
  '1975'.split('').map(n => q1.add(parseInt(n)));
  
  // Populate Q2
  'The Year of the Hare'.split(' ').forEach(word => q2.add(word));

  // Merge the two queues together, but alternate between the two queues as they are added.
  function weave(source1, source2) {
    let queue = new Queue();
    while (q1.peek() || q2.peek()) {
    if (q1.peek()) {
      queue.add(q1.remove());
    }
    
    if (q2.peek()) {
      queue.add(q2.remove());
    }
  }
    
    return queue;
  }
  
  let combinedQueue = weave(q1, q2);
  console.log('Combined Queue', combinedQueue);
  
})();