heapsort.c

#include <stdio.h>

  void swap(int *a, int *b) {
    int tmp = *a;
    *a = *b;
    *b = tmp;
  }

  void heapify(int arr[], int n, int i) {
    int max = i;
    int leftChild = 2 * i + 1;
    int rightChild = 2 * i + 2;

    if (leftChild < n && arr[leftChild] > arr[max])
      max = leftChild;

    if (rightChild < n && arr[rightChild] > arr[max])
      max = rightChild;

    if (max != i) {
      swap(&arr[i], &arr[max]);
      heapify(arr, n, max);
    }
  }

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

    for (int i = n - 1; i >= 0; i--) {
      swap(&arr[0], &arr[i]);

      heapify(arr, i, 0);
    }
  }

  void display(int arr[], int n) {
    for (int i = 0; i < n; ++i)
      printf("%d ", arr[i]);
    printf("\n");
  }

  int main() {
    int arr[] = {55,22,44,11,8,3,1,52,66,26};
    int n = sizeof(arr) / sizeof(arr[0]);

    printf("Original array:\n");
    display(arr, n);
    heapSort(arr, n);

    printf("Sorted array:\n");
    display(arr, n);
  }