PHP merge intervals

mergeintervals.php

<?php

/*
* PHP7 implementation of merging intervals
* It will remove intersections between intervals, for example: [(1, 5), (3,8), (12, 15)] will turn
* into [(1, 8), (12, 15)].
* Based on: https://www.geeksforgeeks.org/merging-intervals/
*/

function merge_intervals(array $data) : array {
	if (count($data) <= 1) {
		return $data;
	}

	$stack = [];

	$stack[] = $data[0];

	for ($i = 1; $i < count($data); $i++) {
		$top = end($stack);

		if ($top['end'] < $data[$i]['start']) {
			array_push($stack, $data[$i]);
		} else if ($top['end'] < $data[$i]['end']) {
			$top['end'] = $data[$i]['end'];
			array_pop($stack);
			array_push($stack, $top);
		}
	}

	return $stack;
}

// Note: intervals must be sorted previously based on start
$d1 = [
	[
		'start' => 0,
		'end' => 200
	],
	[
		'start' => 150,
		'end' => 250
	],
	[
		'start' => 251,
		'end' => 255
	]
];

$r1 = merge_intervals($d1);

var_dump($r1);