--description--

In this challenge you will be creating a Priority Queue. A Priority Queue is a special type of Queue in which items may have additional information which specifies their priority. This could be simply represented with an integer. Item priority will override placement order in determining the sequence items are dequeued. If an item with a higher priority is enqueued after items with lower priority, the higher priority item will be dequeued before all the others.

For instance, let’s imagine we have a priority queue with three items:

[['kitten', 2], ['dog', 2], ['rabbit', 2]]

Here the second value (an integer) represents item priority. If we enqueue ['human', 1] with a priority of 1 (assuming lower priorities are given precedence) it would then be the first item to be dequeued. The collection would look like this:

[['human', 1], ['kitten', 2], ['dog', 2], ['rabbit', 2]]

We’ve started writing a PriorityQueue in the code editor. You will need to add an enqueue method for adding items with a priority, a dequeue method for removing and returning items, a size method to return the number of items in the queue, a front method to return the element at the front of the queue, and finally an isEmpty method that will return true if the queue is empty or false if it is not.

The enqueue should accept items with the format shown above (['human', 1]) where 1 represents the priority. dequeue and front should return only the item's name, not its priority.

--hints--

Your PriorityQueue class should have a enqueue method.

assert(
  (function () {
    var test = new PriorityQueue();
    return typeof test.enqueue === 'function';
  })()
);

Your PriorityQueue class should have a dequeue method.

assert(
  (function () {
    var test = new PriorityQueue();
    return typeof test.dequeue === 'function';
  })()
);

Your PriorityQueue class should have a size method.

assert(
  (function () {
    var test = new PriorityQueue();
    return typeof test.size === 'function';
  })()
);

Your PriorityQueue class should have a front method.

assert(
  (function () {
    var test = new PriorityQueue();
    return typeof test.front === 'function';
  })()
);

Your PriorityQueue class should have an isEmpty method.

assert(
  (function () {
    var test = new PriorityQueue();
    return typeof test.isEmpty === 'function';
  })()
);

Your PriorityQueue class should correctly keep track of the current number of items using the size method as items are enqueued and dequeued.

assert(
  (function () {
    var test = new PriorityQueue();
    test.enqueue(['David Brown', 2]);
    test.enqueue(['Jon Snow', 1]);
    var size1 = test.size();
    test.dequeue();
    var size2 = test.size();
    test.enqueue(['A', 3]);
    test.enqueue(['B', 3]);
    test.enqueue(['C', 3]);
    return size1 === 2 && size2 === 1 && test.size() === 4;
  })()
);

The front method should return the correct item at the front of the queue as items are enqueued and dequeued.

assert(
  (function () {
    var test = new PriorityQueue();
    test.enqueue(['David Brown', 2]);
    var front1 = test.front();
    test.enqueue(['Jon Snow', 1]);
    var front2 = test.front();
    test.dequeue();
    test.enqueue(['A', 3]);
    var front3 = test.front();
    test.enqueue(['B', 3]);
    test.enqueue(['C', 3]);
    test.dequeue();
    var front4 = test.front();
    return (
      front1 === 'David Brown' &&
      front2 === 'Jon Snow' &&
      front3 === 'David Brown' &&
      front4 === 'A'
    );
  })()
);

The isEmpty method should return true when the queue is empty.

assert(
  (function () {
    var test = new PriorityQueue();
    test.enqueue(['A', 1]);
    test.enqueue(['B', 1]);
    test.dequeue();
    var first = test.isEmpty();
    test.dequeue();
    return !first && test.isEmpty();
  })()
);

The priority queue should return items with a higher priority before items with a lower priority and return items in first-in-first-out order otherwise.

assert(
  (function () {
    var test = new PriorityQueue();
    test.enqueue(['A', 5]);
    test.enqueue(['B', 5]);
    test.enqueue(['C', 5]);
    test.enqueue(['D', 3]);
    test.enqueue(['E', 1]);
    test.enqueue(['F', 7]);
    var result = [];
    result.push(test.dequeue());
    result.push(test.dequeue());
    result.push(test.dequeue());
    result.push(test.dequeue());
    result.push(test.dequeue());
    result.push(test.dequeue());
    return result.join('') === 'EDABCF';
  })()
);

--seed--

--seed-contents--

function PriorityQueue () {
  this.collection = [];
  this.printCollection = function() {
    console.log(this.collection);
  };
  // Only change code below this line

  // Only change code above this line
}

--solutions--

function PriorityQueue() {
  this.collection = [];
  this.printCollection = function () {
    console.log(this.collection);
  };
  // Only change code below this line
  this.enqueue = function (newitem) {
    if (this.isEmpty()) {
      return this.collection.push(newitem);
    }

    this.collection = this.collection.reverse();
    var found_index = this.collection.findIndex(function (item) {
      return newitem[1] >= item[1];
    });
    if (found_index === -1) {
      this.collection.push(newitem);
    } else {
      this.collection.splice(found_index, 0, newitem);
    }
    this.collection = this.collection.reverse();
  };
  this.dequeue = function () {
    if (!this.isEmpty()) {
      return this.collection.shift()[0];
    } else {
      return "The queue is empty.";
    }
  };
  this.size = function () {
    return this.collection.length;
  };
  this.front = function () {
    return this.collection[0][0];
  };
  this.isEmpty = function () {
    return this.size() > 0 ? false : true;
  };
  // Only change code above this line
}