Re: can this code be improved

From:
Patricia Shanahan <pats@acm.org>
Newsgroups:
comp.lang.java.programmer
Date:
Sat, 19 Aug 2006 22:12:41 GMT
Message-ID:
<t1MFg.8225$Qf.155@newsread2.news.pas.earthlink.net>
....

Seems to me that topSix should now contain the top six picks but I
could be wrong..


I'm afraid you are wrong, and the apparent over-selection of the high
numbers is due to bugs in your top six selection.

I've written a simple test program comparing the two methods. Take a
look at it, and take it for a test drive:

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class TopSixTest {

   public static void main(String[] args) {
     int[] data = new int[49];
     // Fixed seed for reproducibility
     Random rand = new Random(5);

     for (int i = 0; i < data.length; i++) {
       data[i] = 5;
     }
     System.out.println("data[i]==5");
     test(data);

     for (int i = 0; i < data.length; i++) {
       data[i] = i + 1;
     }
     System.out.println("data[i]==i+1");
     test(data);

     for (int i = 0; i < data.length; i++) {
       data[i] = 100 - i;
     }
     System.out.println("data[i]=100-i");
     test(data);

     testRandomData(rand);
     testRandomData(rand);
     testRandomData(rand);
   }

   /**
    * Test random permutation of numbers from 1000 through 1048
    *
    * @param rand
    */
   private static void testRandomData(Random rand) {
     int[] data = new int[49];
     List<Integer> dataList = new ArrayList<Integer>();
     for (int i = 0; i < data.length; i++) {
       dataList.add(new Integer(1000 + i));
     }
     Collections.shuffle(dataList, rand);
     for (int i = 0; i < data.length; i++) {
       data[i] = dataList.get(i).intValue();
     }
     System.out
         .println("Random permutation of 1000 through 1048");
     test(data);
     System.out.println("Actual positions of largest 6 elements");
     for (int i = 1048; i > 1042; i--) {
       System.out.printf("%d %d", i, dataList
           .indexOf(new Integer(i)));
       System.out.println();
     }
   }

   /**
    * Print the results of both methods on the input data
    *
    * @param data
    * "BigList" data, a 49 element frequency array.
    */
   private static void test(int[] data) {
     int[] printsTop = printsVersion(data.clone());
     int[] patsTop = patsVersion(data.clone());
     for (int i = 0; i < 6; i++) {
       System.out.printf("%d Print's %d Pats's %d", i,
           printsTop[i], patsTop[i]);
       System.out.println();
     }
   }

   private static int[] printsVersion(int[] BigList) {
     int[] topSix = new int[6];
     for (int count = 0; count <= topSix.length - 1; count++) {
       int lIndex = 0;
       int largest = BigList[0];
       for (int x = 0; x <= BigList.length - 1; x++) {
         for (int y = x + 1; y <= BigList.length - 2; y++)
           if (BigList[y] > largest) {
             largest = BigList[y];
             BigList[y] = 0;
             lIndex = y;
             topSix[count] = lIndex;
           }

       }
     }
     return topSix;
   }

   private static int[] patsVersion(int[] BigList) {
     int[] topSix = new int[6];
     for (int count = 0; count < topSix.length; count++) {
       int lIndex = 0;
       int largest = BigList[0];
       for (int x = 1; x < BigList.length; x++) {
         if (BigList[x] > largest) {
           largest = BigList[x];
           lIndex = x;
         }
       }
       topSix[count] = lIndex;
       BigList[lIndex] = 0;
     }
     return topSix;
   }

}

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