Algorithm for finding overlapping events/times

Question

While working on custom calendar, I can\'t figure out how to find time slots that overlaps any other time slot.

Time slots start from 0 to 720 (9am to 9pm with each

Answer 1

To me it is easier to use timestamps for each start and end event, that way you can work with them directly or change them to date objects. To get the value, create a date object for each start and end, then:

var a.start = startDate.getTime();
var a.end = endDate.getTime();

For overlap:

if (a.start <= b.start && a.end > b.start ||
    a.start < b.end && a.end >= b.end) {
    // a overlaps b
}

You can leave them as date objects if you like, the above will work just as well.

Edit

Ok here's a working example:

Assuming a nominal date of 2012-05-15, then the events array looks like:

// Use iso8601 like datestring to make a local date object
function getDateObj(s) {
  var bits = s.split(/[- :]/);
  var date = new Date(bits[0], bits[1] - 1, bits[2]);
  date.setHours(bits[3], bits[4], 0);
  return date;
}

var events = [
  {id: 1, start: getDateObj('2012-05-15 09:00'), end: getDateObj('2012-05-15 09:30')}, 
  {id: 2, start: getDateObj('2012-05-15 09:30'), end: getDateObj('2012-05-15 11:30')}, 
  {id: 3, start: getDateObj('2012-05-15 09:20'), end: getDateObj('2012-05-15 12:00')}, 
  {id: 4, start: getDateObj('2012-05-15 12:20'), end: getDateObj('2012-05-15 12:30')}, 
  {id: 5, start: getDateObj('2012-05-15 18:00'), end: getDateObj('2012-05-15 19:00')}, 
  {id: 6, start: getDateObj('2012-05-15 18:20'), end: getDateObj('2012-05-15 19:20')}
];

function getOverlappingEvents(eventArray) {
  var result = [];
  var a, b;

  // Sort the event array on start time
  eventArray.sort(function(a, b) {
      return a.start - b.start;
    });

  // Get overlapping events
  for (var i=0, iLen=eventArray.length - 1; i b.start) ||
        (a.start < b.end && a.end >= b.end) ) {
       result.push([a.id, b.id]);
    }
  }
  return result;
}

// Run it    
alert(getOverlappingEvents(events).join('\n')); // 1,3 2,3 5,6