Question

Is there an efficient way of calculating whether 2 or more dates overlap in PHP?

Ex.

• Date1: Start1 = 2012-03-10 / End1 = 2012-05-10
• Date2: Start2 = 2012-04-25 / End2 = 2012-06-01
• Date3: Start3 = 2012-07-15 / End3 = 2012-08-20

In the example above Date1 and Date2 overlaps, Date3 is OK.

Answer 1

If your dates are in YYYY-MM-DD format then you can just do a string comparison (they dont have to be valid dates either OR after 1970 if using strtotime() for unix timestamps)

if( ($date1['start']>=$date2['start'] && $date1['start']<=$date2['end']) || ($date1['end']>=$date2['start'] && $date1['end']<=$date2['end']) || ($date1['start']<=$date2['start'] && $date1['end']>=$date2['end']) )
{
    // overlap
}

this checks if start or end of date1 is between the start and end of date2 OR if date1 surrounds date2

.

thanks to @Germann-Arlington –

if($date1['start']<=$date2['end'] && $date2['start']<=$date1['end']) { // overlap }