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Below I have tried the Heap sort algorithm , The first part of the algorithm i.e to Build the Max Heap of the array is working properly , but the second part of the code on the line number 29 i.e DELETION PART , the code doesnt seem to be working.
I am trying to swap the root value of max heap with the last value and then heapify the array again, and let it loop until the for loop stops and gets the keys sorted.

But for some reason I am not getting what's wrong here.

Can you please ahve a quick look below .

Thank you .

Java
```public class demo {

public static void main(String[] args) {

int[] myarray = {4, 8, 1, 2, 9, 11, 0};

heapSort(myarray, myarray.length - 1);

System.out.println(Arrays.toString(myarray));

}

public static void heapSort(int[] array, int n) {
// n = total no. of elements
// n/2 -1 since we started array form 0
//  n/2 if array starts from index 1

// Build max heap
for (int i = n / 2 - 1; i >= 1; i--) {
maxHeapify(array, n, i);
}

//DELETION PART
for (int i = n; i >= 1; i--) {
swap(array, 1, i);
maxHeapify(array, n, 1);
}

}

//  i= start heapify from this index
//  n = total no. of elements
public static void maxHeapify(int[] array, int n, int i) {

int largest = i;
int l = (2 * i) + 1;
int r = (2 * i) + 2;

while (l <= n && array[l] > array[largest]) {
largest = l;
}

while (r <= n && array[r] > array[largest]) {
largest = r;
}

if (largest != i) {
swap(array, largest, i);
maxHeapify(array, n, largest);
}

}

private static void swap(int[] array, int index1, int index2) {

int indexOne = array[index1];
int indextwo = array[index2];

array[index2] = indexOne;
array[index1] = indextwo;
}```

What I have tried:

Tried googling and then landed here
Posted
Updated 15-Sep-20 8:20am
v2

## Solution 1

Compiling does not mean your code is right! :laugh:
Think of the development process as writing an email: compiling successfully means that you wrote the email in the right language - English, rather than German for example - not that the email contained the message you wanted to send.

So now you enter the second stage of development (in reality it's the fourth or fifth, but you'll come to the earlier stages later): Testing and Debugging.

Start by looking at what it does do, and how that differs from what you wanted. This is important, because it give you information as to why it's doing it. For example, if a program is intended to let the user enter a number and it doubles it and prints the answer, then if the input / output was like this:
```Input   Expected output    Actual output
1            2                 1
2            4                 4
3            6                 9
4            8                16```
Then it's fairly obvious that the problem is with the bit which doubles it - it's not adding itself to itself, or multiplying it by 2, it's multiplying it by itself and returning the square of the input.
So with that, you can look at the code and it's obvious that it's somewhere here:
C#
```private int Double(int value)
{
return value * value;
}```

Once you have an idea what might be going wrong, start using the debugger to find out why. Put a breakpoint on the first line of the method, and run your app. When it reaches the breakpoint, the debugger will stop, and hand control over to you. You can now run your code line-by-line (called "single stepping") and look at (or even change) variable contents as necessary (heck, you can even change the code and try again if you need to).
Think about what each line in the code should do before you execute it, and compare that to what it actually did when you use the "Step over" button to execute each line in turn. Did it do what you expect? If so, move on to the next line.
If not, why not? How does it differ?
Hopefully, that should help you locate which part of that code has a problem, and what the problem is.
This is a skill, and it's one which is well worth developing as it helps you in the real world as well as in development. And like all skills, it only improves by use!

BearGryllsRocks9999 15-Sep-20 10:39am
Hey man , Thanks for this.
OriginalGriff 15-Sep-20 11:01am
You're welcome!

## Solution 2

Quote:
But for some reason I am not getting what's wrong here.

Your code do not behave the way you expect, or you don't understand why !

There is an almost universal solution: Run your code on debugger step by step, inspect variables.
The debugger is here to show you what your code is doing and your task is to compare with what it should do.
There is no magic in the debugger, it don't know what your code is supposed to do, it don't find bugs, it just help you to by showing you what is going on. When the code don't do what is expected, you are close to a bug.
To see what your code is doing: Just set a breakpoint and see your code performing, the debugger allow you to execute lines 1 by 1 and to inspect variables as it execute.

Debugger - Wikipedia, the free encyclopedia[^]

Mastering Debugging in Visual Studio 2010 - A Beginner's Guide[^]
Basic Debugging with Visual Studio 2010 - YouTube[^]

http://docs.oracle.com/javase/7/docs/technotes/tools/windows/jdb.html[^]
https://www.jetbrains.com/idea/help/debugging-your-first-java-application.html[^]

The debugger is here to only show you what your code is doing and your task is to compare with what it should do.