Re: Algorithm for performing a rollup

From:
Lew <lew@nospam.lewscanon.com>
Newsgroups:
comp.lang.java.programmer
Date:
Sun, 18 Mar 2007 00:03:00 -0400
Message-ID:
<utGdnfzafsBoJGHYnZ2dnUVZ_o2vnZ2d@comcast.com>
Chris <spam_me_not@goaway.com> wrote:

input:
{"A", "A", "A", "B", "B", "C", "D", "D"}

output:
"A", 3
"B", 2
"C", 1
"D", 2


Arne gave the hint with the Map idea. Here's a version of how I would attempt
such a thing:

First off, let's put the Strings into a List so we can go all Collections.

public class Foo
{

   public static void main( String [] args )
   {
     List< String > starters =
         Arrays.asList( "A", "A", "A", "B", "B", "C", "D", "D" );

     Map< String, Integer > kounts = new HashMap();
     for( String key : starters )
     {
       Integer k = kounts.get( key );
       if ( k == null )
       {
         kounts.put( key, 1 );
       }
       else
       {
         kounts.put( key, k + 1 );
       }
     }

     List< String > outters = new ArrayList< String >();
     outters.addAll( kounts.keySet() );
     Collections.sort( outters );

     for ( String key : outters )
     {
       System.out.println( "\""+ key + "\", "+ kounts.get( key ));
     }
   }
}

-- Lew

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