Re: How to tell if an a date occurs multiple times in an array/collection

From:

Lew <lew@lewscanon.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 18 Nov 2009 11:07:43 -0800 (PST)

Message-ID:

<17c0067e-850f-438c-9cf0-09e2964bd54d@m35g2000vbi.googlegroups.com>

laredotornado wrote:

I have an array of Calendar objects. How can I tell if any of the
object's values in the array occurs more than once (e.g. two objects
with values "01-01-1999 9:00 AM")? If it is easier, I can convert the
Calendar[] array to some other type of collection.

If you load the data into a 'Set <Calendar>' you cannot have any
duplicates.

Set <Calendar> calends =
    new HashSet <Calendar> ( Arrays.asList( getArrayOfCalendars() ));

You can iterate over the array and load the counts into a
'Map <Calendar, Integer>'.

Map <Calendar, Integer> counts =
   new HashMap <Calendar, Integer>
   ( getArrayOfCalendars() .length * 4 / 3 );
for ( Calendar calend : getArrayOfCalendars() )
{
   Integer k = counts.get( calend );
   counts.put( calend, (k == null? 1 : k + 1) );
}
for ( Map.Entry <Calendar, Integer> entry : counts.entrySet() )
{
   if ( entry.getValue() > 1 )
   {
     System.out.println( "Duplicates found for "+ entry.getKey() );
   }
}

This should be about O(n) for performance.

--
Lew