8. Circular Linked List (Front, Rear, Position)

#include <stdio.h>
#include <stdlib.h>

struct node
{
	int info;
	struct node* link;
};

typedef struct node* NODE;

NODE getnode()
{
	NODE x;
	x = malloc(sizeof(struct node));

	return x;

}

NODE insert_front(int item, NODE last)
{
	NODE temp;
	temp = getnode();

	temp->info = item;
	temp->link = NULL;

	if(last == NULL)
	{
		last = temp;
		last->link = last;
		return last;
	}

	else
	temp->link = last->link;

	last->link = temp;
	return last;
}

NODE delete_front(NODE last)
{
	NODE temp;
	NODE first;

	if(last == NULL)
	{
		printf("Nothing to delete\n");
		return NULL;
	}

	if(last->link == last)
	{
		printf("The deleted item is %d\n",last->info);
		free(last);
		return NULL;
	}

	first = last->link;
	last->link = first->link;

	return last;
}


NODE insert_rear(int item, NODE last)
{
	NODE temp;
	temp = getnode();

	temp->info = item;
	temp->link = NULL;

	if(last == NULL)
	{
		last = temp;
		last->link = last;
		return last;
	}

	else
		temp->link = last->link;
		
	last->link = temp;

	return temp;

}

NODE delete_rear(NODE last)
{
	NODE cur;

	if(last == NULL)
	{
		printf("Nothing to delete\n");
		return NULL;
	}

	if(last->link == last)
	{
		printf("Item deleted is %d\n",last->info);
		free(last);
		return NULL;
	}

	cur = last->link;

	while(cur->link != last)
	{
		cur = cur->link;
	}

	cur->link = last->link;
	free(last);
	return cur;
}
/*****************************************************
CODE UNDER PROCESS. CHECK THE FILE CONTAINING SEPERATE CIRCULAR LINKED LIST AT POSITION
*******************************************************/

NODE insert_position(int item, NODE last, int pos)
{
	NODE prev,cur,temp;
	int count = 1;

	temp = getnode();
	temp->info = item;
	temp->link = NULL;


	if(last == NULL && pos == 1)
	{
		temp->link = temp;
		return temp;
	}

	if(last->link == last && pos == 2)
	{
		temp->link = last->link;
		last->link = temp;
		return last;
	} 

	if(pos == 1)
	{
		temp->link = last->link;
		last->link = temp;

		return temp;
	}


	prev = NULL;
	cur = last->link;

	while(cur->link != cur && pos !=count)
	{
		prev = cur;
		cur = cur->link;
		count++;
	}

	if( pos > count)
	{
		printf("Invalid position\n");
		return last;
	}

	prev->link = temp;
	temp->link = cur;


	return last;


}


NODE delete_position(NODE last, int pos)
{
	int count = 1;
	NODE cur,prev,temp;

	if(last == NULL)
	{
		printf("Nothing to delete\n");
		return last;
	}

	if(last->link == last && pos > 1)
	{
		printf("Invalid position\n");		//free(last);
		return last;
	}

	if(pos == 1)
	{
		printf("Deleted item is %d\n",last->info);
		free(last);
		return NULL;
	}

	
	prev = NULL;
	cur = last->link;

	while(cur ->link != last && pos !=count)
	{
		prev = cur;
		cur = cur->link;
		count++;
	}

	if(cur->link == last && pos > count)
	{
		printf("Invalid position\n");
		return last;
	}

	prev->link = cur->link;

	return last;
}


void display(NODE last)
{
	NODE cur;
	cur = last;

	if(last == NULL)
	{
		printf("Nothing to display\n");
		return;
	}



	cur = last;

	while(cur->link != last)
	{
		cur = cur->link;
		printf("%d\n",cur->info);
		
	}


	cur = cur->link;
	printf("%d\n", cur->info);


}




int main()
{
	int item,choice,pos;
	NODE last;

	while(1)
	{

		printf("1. IF\n");
		printf("2. IR\n");
		printf("3. DF\n");
		printf("4. DR\n");
		printf("5. IP\n");
		printf("6. DP\n");
		printf("7. display\n");
		scanf("%d",&choice);


		switch(choice)
		{
			case 1:
				printf("Enter the item: \n");
				scanf("%d",&item);
				last = insert_front(item,last);
				break;

			case 2:
				printf("Enter the item: \n");
				scanf("%d",&item);
				last = insert_rear(item,last);
				break;

			case 3:
				last = delete_front(last);
				break;

			case 4:
				last = delete_rear(last);
				break;
			
			case 5:
				printf("Enter the item: \n");
				scanf("%d",&item);
				printf("Enter the position\n");
				scanf("%d",&pos);
				last = insert_position(item,last,pos);
				break;

			case 6:
				printf("Enter the position\n");
				scanf("%d",&pos);
				last = delete_position(last,pos);
				break;
			
			case 7:
				display(last);
				break;
		}


	}
}