Solved

Count comparisons in sort algorithms??

Posted on 2003-10-27
7
704 Views
Last Modified: 2007-12-19
I'm interested in tracking the number of comparisons in some sort algorithms to compare them.
Im not exactly sure where this counter need to be incremented.  If anyone has any help, thanks.
Some of the sorts I am using include the following.

INSERTION
-------------------------------------------------------------------------------------
template <class T>
void InsertionSort(T A[], int size)
{
  for(int j=1; j<size; j++)
    {
      T key = A[j];
      int i = j - 1;
      while ((i >= 0) && (A[i] > key))
        {
          A[i+1] = A[i];
          i -= 1;
        }
      A[i+1] = key;
    }
}

HEAPSORT
------------------------------------------------------------------------------
template <class T>
void Heapsort(T A[], int size)
{
  BuildHeap(A, size);
  for(i=size; i>1; i--)
    {
      int tmp = A[0];
      A[0] = A[i-1];
      A[i-1] = tmp;
      size--;
      Heapify(A, 1, size);
    }
}

template <class T>
void BuildHeap(T A[], int size)
{
  for(i=size/2; i>0; i--)
    Heapify(A, i, size);
}

template <class T>
void Heapify(T A[], int i, int size)
{
  int  l = 2 * i;
  int  r = 2 * i + 1;
  int largest = 0;

  if(l <= heapsize && A[l-1] > A[i-1])
    largest = l;
  else
    largest = i;

  if(r <= heapsize && A[r-1] > A[largest-1])
    largest = r;
  if(largest != i)
    {
      int tmp = A[i-1];
      A[i-1] = A[largest-1];
      A[largest-1] = tmp;
      Heapify(A, largest, heapsize);
    }
}

0
Comment
Question by:killer455
  • 4
  • 3
7 Comments
 
LVL 7

Expert Comment

by:MrNed
ID: 9631526
Um, you would need to increment a counter everytime you compare elements in the array.

INSERTION - Inside the while loop
HEAPSORT - Twice for each call of Heapify()

I dont think you really want comparisons of non-array elements.
0
 

Author Comment

by:killer455
ID: 9631890
So if I were to place a counter in the heapify function, is there a way I can use that in the original heapsort function in order to produce output after heapsort is done running?
Does this run into making the variable global? If so how is this done?
0
 
LVL 7

Expert Comment

by:MrNed
ID: 9631900
There are many ways you could do it:
1. Use a global variable to count the number of comparisons
2. Create a property for the class and use that to store the count
3. Return the count from the Heapify function

Decide what you're after and have a go. Im not inclined to do too much until I can see you're trying to figure it out.
0
Free Tool: ZipGrep

ZipGrep is a utility that can list and search zip (.war, .ear, .jar, etc) archives for text patterns, without the need to extract the archive's contents.

One of a set of tools we're offering as a way to say thank you for being a part of the community.

 

Author Comment

by:killer455
ID: 9635830
I guess im confused, sorry :(  I modofied it to return the compares??

HEAPSORT
------------------------------------------------------------------------------
template <class T>
void Heapsort(T A[], int size)
{
  BuildHeap(A, size);
  for(i=size; i>1; i--)
    {
      int tmp = A[0];
      A[0] = A[i-1];
      A[i-1] = tmp;
      size--;
      Heapify(A, 1, size);
    }
}

template <class T>
void BuildHeap(T A[], int size)
{
  for(i=size/2; i>0; i--)
    Heapify(A, i, size);
}

template <class T>
void Heapify(T A[], int i, int size)
{
  int compares;
  comapres +=2;
  int  l = 2 * i;
  int  r = 2 * i + 1;
  int largest = 0;

  if(l <= heapsize && A[l-1] > A[i-1])
    largest = l;
  else
    largest = i;

  if(r <= heapsize && A[r-1] > A[largest-1])
    largest = r;
  if(largest != i)
    {
      int tmp = A[i-1];
      A[i-1] = A[largest-1];
      A[largest-1] = tmp;
      Heapify(A, largest, heapsize);
    }
return compares;
}
0
 
LVL 7

Accepted Solution

by:
MrNed earned 60 total points
ID: 9637411
You declared the int compares locally inside the Heapify function. This means that when the function exits, that variable is wiped out. To return it successfully, you need to modify the function declaration to return an int rather than a void.

Since you call the Heapify function recursively, you should capture the return value of the Heapify (A, largest, heapsize) call and add that to you compares counter before returning it.
0
 

Author Comment

by:killer455
ID: 9637633
Well I cant declare it in the heapsort() function because heapify is called both from buildheap and heapsort right?

If I capture it only from Heapify(A, largest, heapsize) won't that make the count on compares inaccurate?

Well sorry for the additional questions, i'm just very confused on how this is done.  If I didnt mention im a beginning programmer so some things that are basically obvious to advanced programmers, are kinda new to me.

Thanks for your continued help.

Ben

0
 
LVL 7

Expert Comment

by:MrNed
ID: 9647698
This is what im thinking, although there are other ways to do it.

template <class T>
void Heapsort(T A[], int size)
{
int count;
  count = BuildHeap(A, size);
  for(i=size; i>1; i--)
    {
      int tmp = A[0];
      A[0] = A[i-1];
      A[i-1] = tmp;
      size--;
      count += Heapify(A, 1, size);
    }
printf("count = %d\n",count);
}

template <class T>
int BuildHeap(T A[], int size)
{
int count=0;
  for(i=size/2; i>0; i--)
    count += Heapify(A, i, size);
return count;
}

template <class T>
int Heapify(T A[], int i, int size)
{
  int count;
  count +=2;
  int  l = 2 * i;
  int  r = 2 * i + 1;
  int largest = 0;

  if(l <= heapsize && A[l-1] > A[i-1])
    largest = l;
  else
    largest = i;

  if(r <= heapsize && A[r-1] > A[largest-1])
    largest = r;
  if(largest != i)
    {
      int tmp = A[i-1];
      A[i-1] = A[largest-1];
      A[largest-1] = tmp;
      count += Heapify(A, largest, heapsize);
    }
return count;
}
0

Featured Post

Free Tool: Path Explorer

An intuitive utility to help find the CSS path to UI elements on a webpage. These paths are used frequently in a variety of front-end development and QA automation tasks.

One of a set of tools we're offering as a way of saying thank you for being a part of the community.

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

Introduction This article is the first in a series of articles about the C/C++ Visual Studio Express debugger.  It provides a quick start guide in using the debugger. Part 2 focuses on additional topics in breakpoints.  Lastly, Part 3 focuses on th…
  Included as part of the C++ Standard Template Library (STL) is a collection of generic containers. Each of these containers serves a different purpose and has different pros and cons. It is often difficult to decide which container to use and …
The goal of the video will be to teach the user the difference and consequence of passing data by value vs passing data by reference in C++. An example of passing data by value as well as an example of passing data by reference will be be given. Bot…
The viewer will learn how to use the return statement in functions in C++. The video will also teach the user how to pass data to a function and have the function return data back for further processing.

830 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