Solved

Java heap sorting questions

Posted on 2010-11-27
3
481 Views
Last Modified: 2012-05-10
Could anyone please help me to understand this code:
That is java class which sorts array.
Questions:
1) What are the numbers of steps you needed to build the heap, and to destroy the heap?
2) How to get the sum of the construction and destruction steps?


Website: http://www.iti.fh-flensburg.de/lang/algorithmen/sortieren/heap/heapen.htm

public class HeapSorter 
{
    private static int[] a;
    private static int n;

    public static void sort(int[] a0)
    {
        a=a0;
        n=a.length;
        heapsort();
    }

    private static void heapsort()
    {
        buildheap();
        while (n>1)
        {
            n--;
            exchange (0, n);
            downheap (0);
        } 
    }

    private static void buildheap()
    {
        for (int v=n/2-1; v>=0; v--)
            downheap (v);
    }

    private static void downheap(int v)
    {
        int w=2*v+1;    // first descendant of v
        while (w<n)
        {
            if (w+1<n)    // is there a second descendant?
                if (a[w+1]>a[w]) w++;
            // w is the descendant of v with maximum label

            if (a[v]>=a[w]) return;  // v has heap property
            // otherwise
            exchange(v, w);  // exchange labels of v and w
            v=w;        // continue
            w=2*v+1;
        }
    }

    private static void exchange(int i, int j)
    {
        int t=a[i];
        a[i]=a[j];
        a[j]=t;
    }

}    // end class HeapSorter

Open in new window

0
Comment
Question by:prog458
  • 2
3 Comments
 
LVL 37

Expert Comment

by:TommySzalapski
ID: 34224072
Since this is most likely a school assignment of some kind, we can't just give out answers but I can sure point you to how to solve it.

I don't see any destruction code, but the entire heap is stored in a single array. So how many steps would it take to 'destroy' that?

Your questions 1 and 2 appear to be the same. This is how you would count the construction steps. Look at how many times the for loop in buildheap runs. So for each of those you do downheap. What is the highest amount of steps that downheap could take? (Hint: the heap is a binary heap so the maximum height is known. You should know what it is too.)

Now just multiply those two numbers together.
0
 

Author Comment

by:prog458
ID: 34228020
Thanks for help i think i am getting there. How can i put those numbers into code. It would be ok with buildheap. How would i do with a downheap?
Theoretically it says h=log(Base2)(N+1)-1 - max hight.The thing is i want to generate that answer from code. Do you have any suggestions.
0
 
LVL 37

Accepted Solution

by:
TommySzalapski earned 500 total points
ID: 34228044
Are you trying to actually count the instructions? In that case just make a global variable start it at 0 and increment it in the loop in downheap and nowhere else.
If you want the runtime, you don't want or need it in the code. They want the average case runtime which you can see is O(n*lg(n))
The current hight of the heap can be calculated as the number of times the loop in downheap runs.
0

Featured Post

How your wiki can always stay up-to-date

Quip doubles as a “living” wiki and a project management tool that evolves with your organization. As you finish projects in Quip, the work remains, easily accessible to all team members, new and old.
- Increase transparency
- Onboard new hires faster
- Access from mobile/offline

Join & Write a Comment

Article by: Nadia
Linear search (searching each index in an array one by one) works almost everywhere but it is not optimal in many cases. Let's assume, we have a book which has 42949672960 pages. We also have a table of contents. Now we want to read the content on p…
Introduction This article is the second of three articles that explain why and how the Experts Exchange QA Team does test automation for our web site. This article covers the basic installation and configuration of the test automation tools used by…
This tutorial will introduce the viewer to VisualVM for the Java platform application. This video explains an example program and covers the Overview, Monitor, and Heap Dump tabs.
Viewers will learn how to properly install Eclipse with the necessary JDK, and will take a look at an introductory Java program. Download Eclipse installation zip file: Extract files from zip file: Download and install JDK 8: Open Eclipse and …

708 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

17 Experts available now in Live!

Get 1:1 Help Now