Question

Return a string for the content of SingleyLinkedList in reverse order by
using recursive algorithm.
Signature: String reverse (Node<E> yourVariableName)
Note: the class name should be SingleyLinkedList

just Convert the reverse method to recursive algorithm.

this is class SingleyLinkedList with reverse method:

class Main {
public static void main(String[] args) {
  
SinglyLinkedList<String> l=new SinglyLinkedList<String>();
l.addFirst("aaa");
l.addFirst("bbbb");
l.addFirst("ccc");
  
  
System.out.print(l.reverse());
}
}

class SinglyLinkedList<E>
{
  
private static class Node<E>
{
    private E element; // reference to the element stored at this node
    private Node<E> next; // reference to the subsequent node in the list
    public Node(E e, Node<E> n)
    {
    element = e;
   next = n;
   }
public E getElement( ) { return element; }
    public Node<E> getNext( ) { return next; }
    public void setNext(Node<E> n) { next = n; }
    }

private Node<E> head = null; // head node of the list (or null if empty)
    private Node<E> tail = null; // last node of the list (or null if empty)
    private int size = 0; // number of nodes in the list
      
    public SinglyLinkedList( ) { }
    public int size( ) { return size; }
    public boolean isEmpty( ) { return size == 0; }
      
    public Node<E> getHead( )
    { // returns the head node
   if (isEmpty( )) return null;
    return head;
    }

      
    public void addFirst(E e)
    { // adds element e to the front of the list
head = new Node<>(e, head); // create and link a new node
    if (size == 0)
    tail = head; // special case: new node becomes tail also
   size++;
}

public void addLast(E e) { // adds element e to the end of the list
Node<E> newest = new Node<>(e, null); // node will eventually be the tail
if (isEmpty())
head = newest; // special case: previously empty list
else
tail.setNext(newest); // new node after existing tail
tail = newest; // new node becomes the tail
size++;
}

public E first() { // returns (but does not remove) the first element
if (isEmpty()) return null;
return head.getElement();
}
  
public E last( )
{ // returns (but does not remove) the last element
if (isEmpty( )) return null;
return tail.getElement( );
}
      
    //implment this Method
public String reverse()
{
String s="";
SinglyLinkedList l2= new SinglyLinkedList();
Node c =head;
//define a new list and add the element of the current list to it in revrse order
//you should use one of the two method addFirst() or addLast() to add in reverse
while (c!=null){
l2.addFirst(c.element);
c=c.getNext();
}

//note that there are no comma after last elment.
Node r =l2.getHead();
while (r!=null){
s=s+Integer.toString((Integer)r.getElement()); //loop the new linked list to store the element on s
if(r.getNext()!=null){
s=s+", "; }
r=r.getNext();}
return s;

}
  
}
  
  

Answer 1

//recursive method
//to return the contents of the list in reverse order
String reverse(Node<E> head) {
if(head == null) {
return "";
}
  
// last node or only one node
if(head.next == null) {
return Integer.toString((Integer)head.getElement());//returning element
}
  
       String s = "";
         
s = reverse(head.getNext()); //recursive call
  
    s= Integer.toString((Integer)head.getElement())+","+s;
    return s;
}