static void heapify(int arr[], int left, int right);
static void sort(int arr[], int left, int right);
static void siftup(int arr[], int left, int right, int key);

void heapsort(int arr[], int left, int right)
{
	/* transform input file into a heap */
	heapify(arr, (right+1)/2, right+1);

	/* sort the heap */
	sort(arr, left+1, right+1);
}

static void heapify(int arr[], int left, int right)
{
	int i;

	/* convert to heap */
	for(i = left; i > 0; i--)
		siftup(arr, i, right, arr[i-1]);
}

static void sort(int arr[], int left, int right)
{
	int i, key;

	for(i = right; i > 1; i--)
	{
		key = arr[i-1];
		arr[i-1] = arr[left-1];		/* move the biggest element to the rightmost position in array */

		/* move up the next biggest element to root */
		siftup(arr, left, i-1, key);
	}
}

static void siftup(int arr[], int left, int right, int key)
{
	int i, j;

	/* move down the tree */
	for(i = left, j = 2*i;  j <= right; i = j, j = 2*i)
	{
		/* j should point to the largest child */
		if(j < right && arr[j-1] < arr[j])
			j++;

		/* if child is smaller or equal to parent, than break out of loop */
		if(key >= arr[j-1])
			break;
		
		/* move up the child element */
		arr[i-1] = arr[j-1];
	}
	arr[i-1] = key;
}