Question

I have a situation that I can not wrap my head around at the moment. Multiple Time Overlaps. I’ve seen many posts on two times that overlap but nothing that has multiple times overlapping.

Here’s the data I would like to place in:

<?php
//RUN EACH Class Selection for Monday
foreach($class as $Classes){
    $time[] = array($ClassStartTime, $ClassEndTime, $classID);
}

OverLapFunction($time);
?>

Which would then post the classID and Overlapping Amount. Has anyone run into this situation before? Or figured out how to do this?

Answer 1

Say your data is like this:

$classes = array(
    array(
       'name' => 'A',
       'day'  => 'Monday',
       'start'=> '08:00AM',
       'end'  => '11:00AM',
    ),
    array(
       'name' => 'B',
       'day'  => 'Monday',
       'start'=> '10:00AM',
       'end'  => '11:30AM',
    ),
    array(
       'name' => 'C',
       'day'  => 'Monday',
       'start'=> '12:00PM',
       'end'  => '04:00PM',
    ),
    array(
       'name' => 'D',
       'day'  => 'Monday',
       'start'=> '03:00PM',
       'end'  => '06:00PM',
    ),
);

You just need a nested foreach, like this:

$overlap = array();
foreach ($classes as $class1) {
    foreach ($classes as $class2) {
        if ($class1['day'] != $class2['day'] || $class1 == $class2) continue;
        if (strtotime($class1['start']) <  strtotime($class2['end']) &&
            strtotime($class1['start']) >= strtotime($class2['start']))
        {
            $array = array($class1['name'], $class2['name']);
            sort($array);
            if (!in_array($array, $overlap)) $overlap[] = $array;
        }
    }
}

Basically, it compares each class to all classes. If $class1 start time is less than $class2 end time and $class1 start time is more than $class2 start time: they overlap. Keep in mind that each class will be compared to each other twice (e.g.: A to B, B to A), so if it doesn’t match on the first pass, it will in the second.

This’ll give you:

Array
(
    [0] => Array
        (
            [0] => B
            [1] => A
        )

    [1] => Array
        (
            [0] => D
            [1] => C
        )

)

If you were to change class D to:

array(
   'name' => 'D',
   'day'  => 'Monday',
   'start'=> '10:00AM',
   'end'  => '03:00PM',
),

…effectively overlapping all classes, you’d get:

Array
(
    [0] => Array
        (
            [0] => A
            [1] => B
        )

    [1] => Array
        (
            [0] => B
            [1] => D
        )

    [2] => Array
        (
            [0] => C
            [1] => D
        )

    [3] => Array
        (
            [0] => A
            [1] => D
        )

)