Example: Heap Sort in C in C

// Heap Sort in C
#include <stdio.h>

// Function to swap two integers
void swap(int *a, int *b) {
    int temp = *a;
    *a = *b;
    *b = temp;
}

// Function to heapify a subtree rooted with node i which is
// an index in arr[]. n is size of heap
void heapify(int arr[], int n, int i) {
    int largest = i; // Initialize largest as root
    int left = 2 * i + 1; // left child
    int right = 2 * i + 2; // right child

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

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

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

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

// Main function to sort an array of given size
void heapSort(int arr[], int n) {
    // Step 1: Build a max-heap (rearrange array)
    // Start from the last non-leaf node and go up to the root
    for (int i = n / 2 - 1; i >= 0; i--) {
        heapify(arr, n, i);
    }

    // Step 2: One by one extract an element from heap
    for (int i = n - 1; i > 0; i--) {
        // Move current root to end
        swap(&arr[0], &arr[i]);

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

// Function to print an array
void printArray(int arr[], int n) {
    for (int i = 0; i < n; ++i) {
        printf("%d ", arr[i]);
    }
    printf("\n");
}

int main() {
    // Step 1: Initialize an array
    int arr[] = {12, 11, 13, 5, 6, 7};
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Original array: ");
    printArray(arr, n);

    // Step 2: Perform heap sort
    heapSort(arr, n);

    printf("Sorted array: ");
    printArray(arr, n);

    return 0;
}