PHP SplPriorityQueue compare() Function

The SplPriorityQueue::compare() function is an inbuilt function in PHP which is used to compare the priority queue elements to place at a particular order in the heap data structure.

Syntax:

int SplPriorityQueue::compare( 
    mixed $priority1 , mixed $priority2 )

Parameters: This function accepts two parameters as mentioned above and described below:

• priority1: This parameter holds the priority of the first node that is  being compared.
• priority2: This parameter holds the priority of the second node that is  being compared.

Return Value: This function returns the result of the comparison function. It returns +ve integer if priority1 is greater than priority2, 0 if both are equal and -ve integer otherwise. 

Example:

<?php

// Declare a class
class priorityQueue extends SplPriorityQueue {
    
    // Compare function to compare priority
    // queue elements
    public function compare($p1, $p2) {
        if ($p1 === $p2) return 0;
        return $p1 < $p2 ? -1 : 1;
    }
}

// Create an object of priority queue
$obj = new priorityQueue();

// Insert elements into the queue
$obj->insert("Geeks",2);
$obj->insert("GFG",1);
$obj->insert("G4G",3);
$obj->insert('G',4);

// Display the priority queue elements
var_dump($obj);

?>

object(priorityQueue)#1 (3) {
  ["flags":"SplPriorityQueue":private]=>
  int(1)
  ["isCorrupted":"SplPriorityQueue":private]=>
  bool(false)
  ["heap":"SplPriorityQueue":private]=>
  array(4) {
    [0]=>
    array(2) {
      ["data"]=>
      string(1) "G"
      ["priority"]=>
      int(4)
    }
    [1]=>
    array(2) {
      ["data"]=>
      string(3) "G4G"
      ["priority"]=>
      int(3)
    }
    [2]=>
    array(2) {
      ["data"]=>
      string(5) "Geeks"
      ["priority"]=>
      int(2)
    }
    [3]=>
    array(2) {
      ["data"]=>
      string(3) "GFG"
      ["priority"]=>
      int(1)
    }
  }
}

Reference: https://www.php.net/manual/en/splpriorityqueue.compare.php