Finding the first available time for 2 users

script.php

<?php

/**

Give the data is this:

[
   {
      "name":"Joe",
      "meetings":[
         ["06:00", "08:00"],
         ["08:15", "09:30"]
      ]
   },
   {
      "name":"Sam",
      "meetings":[
         ["08:00", "08:30"],
         ["12:00", "13:00"]
      ]
   }
]

Step 1: divide into 2 meeting groups
Step 2: find wether the user 1 or 2 has the lastest end time
Step 3: find if the current end time also is the lastest for the second meeting


After this point, the points to scale are:

Available time for more users:

Option 1: group every 2 users and compare all of them with the same algorithm.

Option 2: recursion (this could also avoid multiple layer-loops)

*/


$meeting1 = ['meeting1' => [], 'meeting2' => []];
$meeting1['meeting1'][] = Carbon\Carbon::createFromFormat('H:i', '06:00');
$meeting1['meeting1'][] = Carbon\Carbon::createFromFormat('H:i', '08:00');
$meeting1['meeting2'][] = Carbon\Carbon::createFromFormat('H:i', '08:15');
$meeting1['meeting2'][] = Carbon\Carbon::createFromFormat('H:i', '09:30');


$meeting2 = ['meeting1' => [], 'meeting2' => []];
$meeting2['meeting1'][] = Carbon\Carbon::createFromFormat('H:i', '08:00');
$meeting2['meeting1'][] = Carbon\Carbon::createFromFormat('H:i', '08:30');
$meeting2['meeting2'][] = Carbon\Carbon::createFromFormat('H:i', '12:00');
$meeting2['meeting2'][] = Carbon\Carbon::createFromFormat('H:i', '13:00');


$timeslot = null;
foreach($meeting1 as $m) {
    if (null !== $timeslot && $timeslot->between($m[0], $m[1])) {
        $timeslot = null;
    } elseif (null !== $timeslot) {
        continue;
    }
     
	foreach($meeting2 as $m2) {
        if (null !== $timeslot && $timeslot->between($m2[0], $m2[1])) {
            $timeslot = null;
        } elseif (null !== $timeslot) {
            continue;
        }
        
        $start = $m2[0];
        if ($m[0]->isBefore($m2[0])) {
            $start = $m[0];
        }
        
        $end = $m2[1];
        if ($m[1]->isAfter($m2[1])) {
            $end = $m[1];
        }
        
        $timeslot = $end;
        
    }
}

dd($timeslot);

Version 2 turned the solution to cover more possible cases.