SplPriorityQueue::compare

(PHP 5 >= 5.3.0, PHP 7, PHP 8)

SplPriorityQueue::compare — Compare priorities in order to place elements correctly in the heap while sifting up

Description

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

Compare priority1 with priority2.

Parameters

priority1: The priority of the first node being compared.
priority2: The priority of the second node being compared.

Return Values

Result of the comparison, positive integer if priority1 is greater than priority2, 0 if they are equal, negative integer otherwise.

Note:
Multiple elements with the same priority will get dequeued in no particular order.

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User Contributed Notes 2 notes

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Anonymous ¶

15 years ago

At this time, the documentation sais "Note: Multiple elements with the same priority will get dequeued in no particular order."

If you need elements of equal priority to maintain insertion order, you can use something like:

<?php

class StablePriorityQueue extends SplPriorityQueue {
    protected $serial = PHP_INT_MAX;
    public function insert($value, $priority) {
        parent::insert($value, array($priority, $this->serial--));
    }
}

?>

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Anonymous ¶

1 year ago

To create a min-heap priority queue, and have extract() give you the lowest priority:

class MinPriorityQueue extends SplPriorityQueue {
    public function compare($priority1, $priority2) {
        if ($priority1 === $priority2) return 0;
        return $priority1 > $priority2 ? 1 : -1; 
    }
}

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