Implement a priority queue using SplPriorityQueue

PHP already has a built-in support for implementing a priority queue using SPL. We can use the SplPriorityQueue class to implement our priority queues. Here is the sample previous example using a linked list, but this time we are choosing SPL:

class MyPQ extends SplPriorityQueue { 

    public function compare($priority1, $priority2) { 
    return $priority1 <=> $priority2; 
    }

}

$agents = new MyPQ();

$agents->insert("Fred", 1); 
$agents->insert("John", 2);
$agents->insert("Keith", 3);
$agents->insert("Adiyan", 4);
$agents->insert("Mikhael", 2);

//mode of extraction
$agents->setExtractFlags(MyPQ::EXTR_BOTH); 

//Go to TOP
$agents->top();

while ($agents->valid()) {
    $current = $agents->current();
    echo $current['data'] . "\n";
    $agents->next();
}

This will produce the same result as the linked list example. The added advantage of extending to our own MyPQ class is that we can define whether...