Check if timeranges overlap

Question

I need to check whether an entered time range overlaps with another time range This thread PHP function to check time between the given range? gives a simple explanation on how to check if one date is with a range

I altered the second example function/if-case to the following:

    if(check_slot_range('2014-06-26 06:00:00','2014-06-26 10:00:00', '2014-06-26 07:00:00') OR check_slot_range('2014-06-26 06:00:00','2014-06-26 10:00:00', '2014-06-26 09:00:00')){
      echo "OVERLAP";
    }else{
      echo "NO OVERLAP";
    }

Only the following give an overlap:

• Range '2014-06-26 07:00:00' to '2014-06-26 09:00:00'

• Range '2014-06-26 05:00:00' to '2014-06-26 09:00:00'

• Range '2014-06-26 07:00:00' to '2014-06-26 11:00:00'

This one does not throw the overlap:

• Range '2014-06-26 05:00:00' to '2014-06-26 11:00:00'

How do I need to change the if-clause to catch the overlap for the last example?

For clarification, here the function to compare

    function check_slot_range($start_date, $end_date, $todays_date)
{

  $start_timestamp = strtotime($start_date);
  $end_timestamp = strtotime($end_date);
  $today_timestamp = strtotime($todays_date);

  return (($today_timestamp >= $start_timestamp) && ($today_timestamp <= $end_timestamp));


}

Answer 1

To check for an overlap, you simply check if low1 <= high2 AND high1 >= low2 (instead of date >= low AND date <= high as in the example above)

You can thus create a new function that checks for this condition like this:

function check_ranges_overlap($start_date_1, $end_date_1, $start_date_2, $end_date_2)
{
    $start_timestamp_1 = strtotime($start_date_1);
    $end_timestamp_1 = strtotime($end_date_1);
    $start_timestamp_2 = strtotime($start_date_2);
    $end_timestamp_2 = strtotime($end_date_2);

    return (($start_timestamp_1 <= $end_timestamp_2) && ($end_timestamp_1 >= $start_timestamp_2));
}