Merge K sorted linked lists

//C Program
//Merge K sorted linked lists
#include <stdio.h>

#include <stdlib.h> //for malloc function

//Structure of doubly linked list
struct Node
{
	int data;
	struct Node *next;
	struct Node *prev;
};
//insert Node element of end of linked list
void insert(struct Node **head, int value)
{
	//Create a dynamic node
	struct Node *node = (struct Node *) malloc(sizeof(struct Node));
	if (node == NULL)
	{
		printf("Memory overflow\n");
	}
	else
	{
		//Set data value
		node->data = value;
		node->next = NULL;
		node->prev = NULL;
		if ( *head == NULL)
		{
			*head = node;
		}
		else
		{
			struct Node *temp = *head;
			//Find last node
			while (temp != NULL && temp->next != NULL)
			{
				temp = temp->next;
			}
			//Add new node to last position
			temp->next = node;
			node->prev = temp;
		}
	}
}
//This function are displayed group of given linked lists
void print_list(struct Node *list[], int size)
{
	if (size <= 0)
	{
		printf("Empty linked list");
	}
	else
	{
		struct Node *temp = NULL;
		for (int i = 0; i < size; i++)
		{
			temp = list[i];
			//Traverse doubly linked list 
			while (temp != NULL)
			{
				//print node value
				printf("%3d", temp->data);
				temp = temp->next;
			}
			printf("\n");
		}
		printf("\n");
	}
}
// This function arrange the linked list node in sorted order
// by using swapping node operation
void update_record(struct Node *head)
{
	int temp = 0;
	//Sort given linked list
	while (head != NULL && head->next != NULL && head->next->data < head->data)
	{
		temp = head->data;
		head->data = head->next->data;
		head->next->data = temp;
		head = head->next;
	}
}
//This function is sorted given linked list elements
void sort(struct Node *auxiliary[], int size)
{
	int position = -1, source = -1, temp = 0;
	//Get first node position of given linked lists
	for (int i = 0; i < size && position == -1; ++i)
	{
		if (auxiliary[i] != NULL)
		{
			//When list i are not null
			position = i;
		}
	}
	if (position != -1)
	{
		//When need to sort list elements
		source = -1;
		temp = position;
		//Find smallest node location of lists
		for (int i = position + 1; i < size; ++i)
		{
			if (auxiliary[i] != NULL && auxiliary[i]->data < auxiliary[temp]->data)
			{
				source = i;
				temp = i;
			}
		}
		if (source != -1)
		{
			temp = auxiliary[position]->data;
			//Swap node value
			auxiliary[position]->data = auxiliary[source]->data;
			auxiliary[source]->data = temp;
			//after swap arrange second list elements in sorted order. 
			update_record(auxiliary[source]);
		}
		//visit next node
		auxiliary[position] = (auxiliary[position])->next;
		//Recursive executed, until when given list need sorting operation
		sort(auxiliary, size);
	}
}
//This function are handle the request to sort elements in given linked lists
//Assuming that given linked list contains sorted elements
void *sort_list(struct Node *list[], int size)
{
	//This is used to store first node of each linked list
	struct Node *auxiliary[size];
	int i = 0;
	//This loop are obtain the first node of each linked list
	for (i = 0; i < size; i++)
	{
		//Get first node of lists
		auxiliary[i] = list[i];
	}
	sort(auxiliary, size);
	struct Node *head = list[0];
	i = 0;
	//This loop are combining linked lists nodes
	while (i < size - 1)
	{
		if (head->next == NULL)
		{
			i++;
			head->next = list[i];
			//This is not important but given multiple lists and each list are share their nudes to other
			list[i] = list[0];
		}
		head = head->next;
	}
}
//This function are display given linked list elements 
void display(struct Node *head)
{
	while (head != NULL)
	{
		//print node value
		printf("%3d", head->data);
		head = head->next;
	}
}
int main()
{
	struct Node *list[4] = {
		NULL
	};
	//Add Linked list elements
	//Add first list element
	insert( & list[0], 1);
	//similar way add other elements
	insert( & list[0], 3);
	insert( & list[0], 14);
	insert( & list[0], 19);
	//Add second list element
	insert( & list[1], 0);
	insert( & list[1], 0);
	insert( & list[1], 2);
	insert( & list[1], 4);
	//Add third list element
	insert( & list[2], -3);
	insert( & list[2], 5);
	insert( & list[2], 8);
	insert( & list[2], 12);
	insert( & list[2], 12);
	insert( & list[2], 15);
	insert( & list[2], 17);
	//Add fourth list element
	insert( & list[3], 8);
	insert( & list[3], 15);
	insert( & list[3], 44);
	//Get size of linked list
	int k = sizeof(list) / sizeof(list[0]);
	//Before 
	print_list(list, k);
	sort_list(list, k);
	printf(" After Sort \n ");
	//After sort display the linked list elements
	display(list[0]);
	return 0;
}

Output

  1  3 14 19
  0  0  2  4
 -3  5  8 12 12 15 17
  8 15 44

 After Sort
  -3  0  0  1  2  3  4  5  8  8 12 12 14 15 15 17 19 44