Merge sort for singly linked list

// C Program 
// Merge sort for singly linked list
#include <stdio.h>
#include <stdlib.h> //for malloc function

// Linked List LinkNode
struct LinkNode
{
	int data;
	struct LinkNode *next;
};
// Singly linked list 
struct SingleLL
{
	struct LinkNode *head;
	struct LinkNode *tail;
};
// Returns the new linked list
struct SingleLL *newLinkedList()
{
	// Create memory of head and tail Nodes
	struct SingleLL *sll = (struct SingleLL *) malloc(sizeof(struct SingleLL));
	if (sll == NULL)
	{
		printf("Memory overflow\n");
	}
	else
	{
		sll->head = NULL;
		sll->tail = NULL;
	}
	return sll;
}
// Add new Node at end of linked list 
void appendNode(struct SingleLL *sll, struct LinkNode *node)
{
	if (sll->head == NULL)
	{
		sll->head = node;
	}
	else
	{
		// Append the node at last position
		sll->tail->next = node;
	}
	sll->tail = node;
}
// Handles the request of adding new node in linked list
void addNode(struct SingleLL *sll, int data)
{
	// Create dynamic node
	struct LinkNode *node = (struct LinkNode *) malloc(sizeof(struct LinkNode));
	if (node == NULL)
	{
		printf("Memory overflow to Create LinkNode\n");
		return;
	}
	else
	{
		// Set initial node value
		node->data = data;
		node->next = NULL;
	}
	appendNode(sll, node);
}
// Display linked list element
void display(struct SingleLL *sll)
{
	if (sll->head == NULL)
	{
		printf("\n Empty linked list\n");
		return;
	}
	struct LinkNode *temp = sll->head;
	// iterating linked list elements
	while (temp != NULL)
	{
		printf(" %d →", temp->data);
		// Visit to next node
		temp = temp->next;
	}
	printf(" NULL\n");
}
// Returns the middle node of given linked list
struct LinkNode *findMiddle(struct LinkNode *node)
{
	// Define auxiliary variable
	struct LinkNode *middle = node;
	struct LinkNode *fast = node;
	// Execute the loop until here fast variable is not null 
	// and its two next node are exist
	while (fast != NULL && fast->next != NULL && fast->next->next != NULL)
	{
		// visit to second next node
		fast = fast->next->next;
		// visit to next node
		middle = middle->next;
	}
	// Return the middle node
	return middle;
}
// sorted merging of node in given sorted sublist
struct LinkNode *sortedMerge(struct LinkNode *x, struct LinkNode *y)
{
	if (x == NULL)
	{
		return y;
	}
	else if (y == NULL)
	{
		return x;
	}
	else
	{
		if (x->data <= y->data)
		{
			x->next = sortedMerge(x->next, y);
			return x;
		}
		else
		{
			y->next = sortedMerge(x, y->next);
			return y;
		}
	}
}
// Splitting the linked list node, 
// And combine node using sorted merge function
struct LinkNode *mergeSort(struct LinkNode *node)
{
	if (node == NULL || node->next == NULL)
	{
		return node;
	}
	else
	{
		// Find middle node
		struct LinkNode *middle = findMiddle(node);
		// Sort right sublist
		struct LinkNode *right = mergeSort(middle->next);
		// split the linked list
		middle->next = NULL;
		// Sort left sublist
		struct LinkNode *left = mergeSort(node);
		return sortedMerge(left, right);
	}
}
// Handles the request to perform merge sort
void sort(struct SingleLL *sll)
{
	if (sll->head == NULL)
	{
		return;
	}
	// Set new head
	sll->head = mergeSort(sll->head);
	struct LinkNode *node = sll->head;
	// Find last node
	while (node != NULL && node->next != NULL)
	{
		// visit to next node
		node = node->next;
	}
	// Set new tail
	sll->tail = node;
}
int main()
{
	// Create a linked list
	struct SingleLL *sll = newLinkedList();
	// Given of linked list
	// 3 → 11 → 8 → 5 → -2 → 16 → 9 → NULL
	// Construct linked list
	addNode(sll, 3);
	addNode(sll, 11);
	addNode(sll, 8);
	addNode(sll, 5);
	addNode(sll, -2);
	addNode(sll, 16);
	addNode(sll, 9);
	printf("\n Before sort \n");
	display(sll);
	// perform sort
	sort(sll);
	printf("\n After sort \n");
	display(sll);
	return 0;
}

Output

 Before sort
 3 → 11 → 8 → 5 → -2 → 16 → 9 → NULL

 After sort
 -2 → 3 → 5 → 8 → 9 → 11 → 16 → NULL