Heapsort swap and comparisons. How to pass them through two functions

Question

I'm trying to count swaps and comparisons of Heap Sort algorithm in c++. So far I have written main function and also two methods(both for heap sort algorithm).

int main()
{
    int countComp = 0, countSwap = 0;
    int arr[] = {12, 11, 13, 5, 6, 7};
    int n = sizeof(arr)/sizeof(arr[0]);

    heapSort(arr, n, countComp, countSwap);

    cout << "Sorted array is \n";
    printArray(arr, n);

    cout << "comparisons: " << countComp <<  " swaps: " << countSwap << endl;
}

I know I'm making somekind of logical mistake because it is very confusing to me to pass variables through parameters and then call those functions with recursion.

void heapify(int arr[], int n, int i, int& countComparisons, int& countSwaps)
{
    int largest = i;  // Initialize largest as root
    int l = 2*i + 1;  // left = 2*i + 1
    int r = 2*i + 2;  // right = 2*i + 2

    // If left child is larger than root
    if (l < n && arr[l] > arr[largest])
    {
        countComparisons++;
        largest = l;
    }

    // If right child is larger than largest so far
    if (r < n && arr[r] > arr[largest])
    {
        countComparisons++;
        largest = r;
    }

    // If largest is not root
    if (largest != i)
    {
        countSwaps++;
        swap(arr[i], arr[largest]);

        // Recursively heapify the affected sub-tree
        heapify(arr, n, largest, countComparisons, countSwaps);
    }
}

// main function to do heap sort
void heapSort(int arr[], int n, int& countComparisons, int& countSwaps)
{
    // Build heap (rearrange array)
    for (int i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i, countComparisons, countSwaps);

    // One by one extract an element from heap
    for (int i=n-1; i>=0; i--)
    {
        countSwaps++;
        // Move current root to end
        swap(arr[0], arr[i]);

        // call max heapify on the reduced heap
        heapify(arr, n, 0, countComparisons, countSwaps);
    }
}

I'm pretty sure mistake is related with parameter which is being passed by reference. Could someone correct me please. I'm stuck with this problem. Or maybe there is a better way to count swaps and comparisons?

If I run this, I get answer : comparisons: 12 swaps: 16

Answer 1

Sorted array is
13, 12, 11, 5, 7, 6,
comparisons: 12 swaps: 16

You have an error in heapSort which lead to the wrong sort result. It also causes increased number of comparisons and swaps in a failed attempt to sort successfully. Change n to i in the second call to heapify

void heapSort(int arr[], int n, int& countComparisons, int& countSwaps)
{
    for(int i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i, countComparisons, countSwaps);

    for(int i = n - 1; i >= 0; i--)
    {
        countSwaps++;
        swap(arr[0], arr[i]);
        //heapify(arr, n, 0, countComparisons, countSwaps);
        heapify(arr, i, 0, countComparisons, countSwaps); //<=== changed `n` to `i`
    }
}

Result:

Sorted array is
5, 6, 7, 11, 12, 13,
comparisons: 7 swaps: 11

Test on ideone