[SOLVED] How to check if a list of intervals (Joda-Time) fully covers a month in Java

How to check if a list of intervals (Joda-Time) fully covers a month in Java

I'm using Joda-Time library in Java to keep track a list of time intervals. I want to check if a list of Interval objects fully covers every minute of a month. There's about 30 intervals of varying length from a few hours to a few days.

I thought a cheap way to do this is to sort the list of intervals by start time, then successively check if there is a break between the intervals within the range of the month. If yes, then the month is not fully covered.

I'm stuck on the first part, sorting the list. I planned to use Arrays.sort(), but it needs the elements to implement the comparable interface. However, after looking through the source, Joda-Time's Interval class doesn't seem to have one I can override, and I can't extend it to write my own compareTo method.

Other than writing my own sorting method, anyone know an easier way to accomplish this? Thanks

Solution

You can use next method

static boolean covers(Interval month, List<Interval> intervals)
{
  //assumes intervals are sorted already on start times
  final MutableInterval monthInterval = new MutableInterval(month);
  start: for (final Interval interval : intervals)
  {
     if (interval.getStartMillis() <= monthInterval.getStartMillis()
        && interval.getEndMillis() > monthInterval.getStartMillis())
     {
        if (interval.getEndMillis() > monthInterval.getEndMillis())
        {
           return true;
        }
        monthInterval.setStartMillis(interval.getEndMillis());
        // continue start;  // loop continues regardless
     } else {
           if (interval.overlaps(month)) return false;
     }
  }
  return monthInterval.getStartMillis()== monthInterval.getEndMillis();
}

Example

   static final List<Interval> intervals = new ArrayList<Interval>();
   static
   {
      intervals.add(new Interval(new DateTime(1990, 05, 15, 00, 00, 00, 00), new DateTime(1990, 05, 18, 00, 00, 00, 00)));
      intervals.add(new Interval(new DateTime(1990, 04, 28, 00, 00, 00, 00), new DateTime(1990, 05, 18, 00, 00, 00, 00)));
      intervals.add(new Interval(new DateTime(1990, 05, 17, 00, 00, 00, 00), new DateTime(1990, 05, 21, 00, 00, 00, 00)));
      intervals.add(new Interval(new DateTime(1990, 05, 21, 00, 00, 00, 00), new DateTime(1990, 05, 29, 00, 00, 00, 00)));
      intervals.add(new Interval(new DateTime(1990, 05, 22, 00, 00, 00, 00), new DateTime(1990, 05, 25, 00, 00, 00, 00)));
      intervals.add(new Interval(new DateTime(1990, 05, 27, 00, 00, 00, 00), new DateTime(1990, 06, 02, 00, 00, 00, 00)));
   }

   public static void main(String[] args)
   {
      final DateTime startOfMonth = new DateTime(1990, 05, 01, 00, 00);
      final Interval monthInterval = new Interval(startOfMonth, startOfMonth.plusMonths(1));

      covers(monthInterval, intervals);
   }

   static boolean covers(Interval month, List<Interval> intervals)
   {
      final MutableInterval monthInterval = new MutableInterval(month);
      start: for (final Interval interval : intervals)
      {
         if (interval.getStartMillis() <= monthInterval.getStartMillis()
            && interval.getEndMillis() > monthInterval.getStartMillis())
         {
            if (interval.getEndMillis() > monthInterval.getStartMillis())
            {
               return true;
            }
            monthInterval.setStartMillis(interval.getEndMillis());
            continue start;
         }
      }
      return monthInterval.getStartMillis()== monthInterval.getEndMillis();
   }