Question

iImplement a Singly Linked List detectLoop in Java, it would check whether the linked list contains a loop. Print true if yes, false if not.
Test by using the following code:

                LL<Integer> L = new LL<>();
        for (int i = 1000; i > 0; i-=3) sl.add(i);   
                try {
                        L.insert(122, L.getNode(70), L.getNode(21));
                        if (L.detectLoop()) System.out.println("True");
                        else System.out.println("False.");
            }

       catch(Exception e){
                        e.printStackTrace();
                }

class Linkedlist<E>{
        private static class Node<E>{
                private E element;
                private Node<E> next;
                public Node(E e, Node<E> n){
                        element = e;
                        next = n;
                }
                public E getE(){
                        return element;
                }
                public Node<E> getNext(){
                        return next;
                }
                public void setE(E e){
                        element = e;
                }
                public void setNext(Node<E> n){
                        next = n;
                }
        }
        private Node<E> head;
        public Linkedlist(){
                head = null;
        }
        public void add(E e){
                Node<E> temp = new Node<>(e, head);                 
                head = temp;
        }
        public void insert(E e, Node<E> p, Node<E> n){
                p.setNext(new Node<>(e, n));      
        }
        public Node<E> getNode(int i) throws Exception{
                Node<E> temp = head;
                while (i > 0){
                        if (temp == null) throw new Exception("OoB");
                        temp = temp.getNext();
                        i--;
                }
                return temp;
        }
        
}

Answer 1

As you asked me to write the detectloop function using your code provided by you I created a new function detectloop in class Linkedlist. I used Floyd's cycle finding algo to find a loop in the linked list. After that, I created a LinkedList_test class to test the detectloop function. Every change I have done in the code are in BOLD.

Code:-

class Linkedlist<E>

{

    private static class Node<E>

    {

        private E element;

        private Node<E> next;

       

        public Node(E e, Node<E> n)

        {

            element = e;

            next = n;

        }

       

        public E getE()

        {

            return element;

        }

       

        public Node<E> getNext()

        {

            return next;

        }

       

        public void setE(E e)

        {

            element = e;

        }

                

        public void setNext(Node<E> n)

        {

            next = n;

        }

    }

   

    private Node<E> head;

   

    public Linkedlist()

    {

        head = null;

    }

   

    public void add(E e)

    {

        Node<E> temp = new Node<>(e, head);                

        head = temp;

    }

    public void insert(E e, Node<E> p, Node<E> n)

    {

        p.setNext(new Node<>(e, n));     

    }

       

    public Node<E> getNode(int i) throws Exception

   {

        Node<E> temp = head;

        while (i > 0)

        {

            if (temp == null) throw new Exception("OoB");

            temp = temp.getNext();

            i--;

        }

        return temp;

    }

   

    //i am creating detect loop function using Floydd's Cycle finding algoritham

    public boolean detectLoop()

    {

        //created two pointers slow and fast

        //slow pointer move by one Node

        //fast pointer move by two Node

        Node<E> fast=head;

        Node<E> slow=head;

       

        //loop is going to run until every condiotn in loop is true

        while(fast!=null && slow!=null &&fast.next!=null)

        {

            //fast move by two node

            fast=fast.next.next;

            //slow move by one node

            slow=slow.next;

           

            //if they point to same node anytime that means there is a loop in the linked list

            if(fast==slow)

            {

                return true;

            }

           

        }

        return false;

    }

       

}

public class Linkedlist_test

{

    public static void main (String[] args)

    {

        Linkedlist<Integer> L = new Linkedlist<>();

        for (int i = 1000; i > 0; i-=3)

        L.add(i);  

        try

        {

            L.insert(122, L.getNode(70), L.getNode(21));

            if (L.detectLoop()) System.out.println("True");

            else System.out.println("False.");

        }

        catch(Exception e)

        {

            e.printStackTrace();

        }

    }

}

output:-