import java.util.*;

public class LinkedMenu {

Node head;

static class Node

{

int data;

Node next;

Node(int d)

{

data=d;

next=null;

}

}

public static LinkedMenu add(LinkedMenu li,int b)

{

Node newNode=new Node(b);

if(li.head==null)

{

li.head=newNode;

}

else

{

Node last=li.head;

while(last.next!=null)

{

last=last.next;

}

last.next=newNode;

}

return li;

}

public static LinkedMenu insert(LinkedMenu li,int index,int data)

{

Node newNode=new Node(data);

Node count=li.head;

int c=0;

if(li.head==null)

{

li.head=newNode;

}

while(count.next!=null)

{

c++;

count=count.next;

}

if(c>index)

{

if(index==0)

{

Node start=li.head;

li.head=newNode;

newNode.next=start;

}

else if(c==index)

{

Node last=li.head;

while(last.next!=null)

{

last=last.next;

}

last.next=newNode;

}

else

{

Node curr=li.head;

int a=0;

Node d=curr.next;

while(a<index-1)

{

curr=curr.next;

d=d.next;

a++;

}

curr.next=newNode;

newNode.next=d;

}

}

else

{

System.out.println("Invalid index");

}

return li;

}

public static LinkedMenu delete(LinkedMenu li,int index)

{

Node c=li.head;

if(li.head==null)

{

System.out.println("linked list does not exist");

}

int count=0;

while(c.next!=null)

{

count++;

c=c.next;

}

if(index>count)

{

System.out.println("Invalid input");

}

else

{

Node d=li.head;

int a=0;

if(index==0)

{

li.head=d.next;

}

else if(index==count)

{

d=li.head;

while(d.next.next!=null)

{

d=d.next;

}

d.next=null;

}

else

{

Node dd=d.next.next;

while(a<(index-1))

{

d=d.next;

dd=dd.next;

a++;

}

d.next=dd;

}

}

return li;

}

public static LinkedMenu display(LinkedMenu li)

{

Node curr=li.head;

if(li.head==null)

{

System.out.println("Linked list does not exist");

}

else

{

while(curr.next!=null)

{

System.out.print(curr.data);

curr=curr.next;

}

System.out.print(curr.data);

//System.out.println(" ");

}

return li;

}

public static void main(String[] args)

{

LinkedMenu li=new LinkedMenu();

Scanner sc=new Scanner(System.in);

int index;

int n;

/* int n=sc.nextInt();

for(int i=0;i<n;i++)

{

int b=sc.nextInt();

add(li,b);

}*/

String s="yes";

while(s.equals("yes")||s.equals("y"))

{

System.out.println("enter your choice");

System.out.println("1:Make a list");

System.out.println("2:insert");

System.out.println("3:Delete");

System.out.println("4:Display");

int opt=sc.nextInt();

switch(opt)

{

case 1:

System.out.println("Enter the number of elements:");

n=sc.nextInt();

System.out.println("Enter the elements: ");

for(int i=0;i<n;i++)

{

int b=sc.nextInt();

add(li,b);

}

break;

case 2:

if(li.head==null)

{

System.out.println("no list found ");

System.out.println("make a list first");

System.out.println("Enter the number of elements:");

n=sc.nextInt();

System.out.println("Enter the elements: ");

for(int i=0;i<n;i++)

{

int b=sc.nextInt();

add(li,b);

}

}

System.out.println("Enter the index where you want to insert");

index=sc.nextInt();

int data=sc.nextInt();

insert(li,index,data);

System.out.println("Do you want to continue");

s=sc.next();

break;

case 3:

if(li.head==null)

{

System.out.println("no list found ");

System.out.println("make a list first");

System.out.println("Enter the number of elements:");

n=sc.nextInt();

System.out.println("Enter the elements: ");

for(int i=0;i<n;i++)

{

int b=sc.nextInt();

add(li,b);

}

}

System.out.println("Enter the index where you want to delete");

index=sc.nextInt();

delete(li,index);

System.out.println("Do you want to continue");

s=sc.next();

break;

case 4:

if(li.head==null)

{

System.out.println("no list found ");

System.out.println("make a list first");

System.out.println("Enter the number of elements:");

n=sc.nextInt();

System.out.println("Enter the elements: ");

for(int i=0;i<n;i++)

{

int b=sc.nextInt();

add(li,b);

}

}

System.out.println("The elements of the list are:");

display(li);

System.out.println("Do you want to continue");

s=sc.next();

break;

default:

System.out.println("the option tha you have entered is not valid");

System.out.println("Do you want to continue");

s=sc.next();

}

}

if(s.equals("no")||s.equals("n"))

{

System.out.println("Thanks");

}

}

}