Determine when two datetime ranges overlap

Question

I have two datetime intervals, and I want to identify the overlapping period between them. For instance, if I have intervals:

• 01-12-2023 01:00:00 to 12-12-2023 15:00:00
• 10-12-2023 11:00:00 to 24-12-2023 16:00:00

I need to retrieve the common interval, which in this case is 10-12-2023 11:00:00 to 12-12-2023 15:00:00. How can I achieve this in PHP, either using native functions or a library like Carbon?

Here is my code :

<?php
require 'vendor/autoload.php';
use Carbon\Carbon;

$range1Start = Carbon::parse('2023-12-01 01:00:00');
$range1End = Carbon::parse('2023-12-12 15:00:00');

$range2Start = Carbon::parse('2023-12-10 11:00:00');
$range2End = Carbon::parse('2023-12-24 16:00:00');

if ($range1Start->lessThan($range2End) && $range2Start->lessThan($range1End)) {
    // Calculate the overlapping period
    $overlapStart = $range1Start->max($range2Start);
    $overlapEnd = $range1End->min($range2End);

    echo "Overlap: {$overlapStart->toDateTimeString()} to {$overlapEnd->toDateTimeString()}\n";
} else {
    echo "No overlap.\n";
}

Answer 1

There is a simple algorithm you can follow:

1. Determine the latest start and earliest end.
2. If the latest start is greater than earliest end: there is no overloapping.
3. Otherwise overlapping is take a place between latest start and earliest end.

Here is an example of implementation:

<?php
require 'vendor/autoload.php';
use Carbon\Carbon;

$range1Start = Carbon::parse('2023-12-01 01:00:00');
$range1End = Carbon::parse('2023-12-12 15:00:00');

$range2Start = Carbon::parse('2023-12-10 11:00:00');
$range2End = Carbon::parse('2023-12-24 16:00:00');


$maxStart = $range1Start->max($range2Start);
$minEnd = $range1End->min($range2End);

if ($maxStart->lessThan($minEnd)) {
    echo "Overlap: {$maxStart->toDateTimeString()} to {$minEnd->toDateTimeString()}\n";
} else {
    echo "No overlap.\n";
}