Question

JAVA - Circular Doubly Linked List

Does anybody could help me with this method below(previous)?

public E previous() {
// Returns the previous Element
return null;
}

Explanation:

We have this class with these two implemented inferfaces:

New Java Class Java Class Create a new Java class. Source folder: cmoore/src Browse... Package: edu.ics 211.h06 Browse... Enclosing type: Browse... Name: Modifiers: CircularDoublyLinkedList<E> public package abstract final protected private static Superclass: java.lang.Object Browse... Interfaces: edu.ics 211.04.IList211<E> java.lang.Iterable<E> Add... Remove Which method stubs would you like to create? public static void main(String[] args) Constructors from superclass Inherited abstract methods Do you want to add comments? (Configure templates and default value here) Generate comments Cancel Finish

The interfaces are:

package edu.ics211.h04;

/**
 * Interface for a List211.
 *
 * @author Cam Moore
 * @param  the generic type of the Lists.
 */
public interface IList211 {
  /**
   * Gets the item at the given index.
   * @param index the index.
   * @return the item at the given index.
   */
  E get(int index);

  /**
   * Sets the item at the given index.
   * @param index the index.
   * @param element the new element to set.
   * @return the old element at index.
   */
  E set(int index, E element);

  /**
   * Returns the index of the given obj or -1.
   * @param obj the object to find.
   * @return the index of the given obj or -1.
   */
  int indexOf(Object obj);

  /**
   * Returns the size of this list.
   * @return the size of this list.
   */
  int size();

  /**
   * Adds e to the end of the list.
   * @param e the item to add.
   * @return true if successful, false otherwise.
   */
  boolean add(E e);

  /**
   * Adds element to the list at the given index.
   * @param index the index.
   * @param element the element to add.
   */
  void add(int index, E element);

  /**
   * Removes the element at the given index.
   * @param index the index.
   * @return The element removed from the list.
   */
  E remove(int index);
}

Inside CircularDoublyLinkedList we have another class that implements

public interface ListIterator {
  void add(E e); // Inserts the specified element to the list. (Optional for this assignment)
  boolean hasNext(); // Returns true if this list iterator has more elements while traversing in the forward direction.
  boolean hasPrevious(); // Returns true if this list iterator has more elements while traversing in the reverse direction.
  E next(); // Returns the next Element.
  int nextIndex(); // Returns the index of the next element.
  E previous(); // Returns the previous Element
  int previousIndex(); // Returns the index of the previous element.
  void remove(); // Removes from the list the last element that was returned.
  void set(E e); // Replaces the last element returned. (Optional for this assignment)

}

Thank you very much for your help!!

Answer 1

You can refer the below C code for finding the previous element of Circular Doubly Linked list:

#include <stdio.h>

#include <stdlib.h>

struct node

{   int val;

    struct node *next;

    struct node *prev;    

};

typedef struct node n;

void PreviousElement();

n *new, *ptr, *prev, *ptr_prev=NULL;

n *first = NULL, *last = NULL;

int number = 0;

void main()

{  
     n *previous;
     previous=PreviousElement();
}    
n PreviousElement()

{

    int key, i, f = 0;

    printf("\nEnter the value of which you want to find previous element:");

    scanf("%d", &key);

    if (first == last && first == NULL)

        printf("\nList is empty no elemnets in list to search");

    else

    {

        for (ptr = first,i = 0;i < number;i++,ptr = ptr->next)

        {   
            if (ptr->val == key)

            {   ptr_prev=ptr->prev;        

                f = 1;

return  ptr_prev;

            }    

        }

        if (f == 0)

            printf("\n the value is not found in linkedlist");

    }

return ptr_prev;

  }