Heapsort.c

#include <stdio.h>

void heapify(int arr[], int n, int i)
{
    int largest = i;
    int left = 2 * i + 1;
    int right = 2 * i + 2;

    if (left < n && arr[left] > arr[largest])
        largest = left;

    // If the right child is larger than the largest so far
    if (right < n && arr[right] > arr[largest])
        largest = right;

    // If the largest element is not the root
    if (largest != i)
    {
        // Swap the largest element with the root
        int temp = arr[i];
        arr[i] = arr[largest];
        arr[largest] = temp;

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

void heapsort(int arr[], int n)
{
    // Build a max heap
    int i;
    for (i = n / 2 - 1; i >= 0; i--)
        heapify(arr, n, i);

    // One by one extract elements from the heap
    for (i = n - 1; i > 0; i--)
    {
        // Move the current root to the end
        int temp = arr[0];
        arr[0] = arr[i];
        arr[i] = temp;

        // Call max heapify on the reduced heap
        heapify(arr, i, 0);
    }
}

int main()
{
    int arr[] = {12, 21, 13, 5, 1, 7};
    int i;
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Original array: ");
    for (i = 0; i < n; i++)
        printf("%d ", arr[i]);

    heapsort(arr, n);

    printf("\nSorted array: ");
    for (i = 0; i < n; i++)
        printf("%d ", arr[i]);

    return 0;
}