Question

Java queue linked list

/*
* Complete the enqueue(E val) method
* Complete the dequeue() method
* Complete the peek() method
* No other methods/variables should be added/modified
*/
public class A3Queue {
   /*
   * Grading:
   * Correctly adds an item to the queue - 1pt
   */
   public void enqueue(E val) {
       /*
       * Add a node to the list
       */
   }
   /*
   * Grading:
   * Correctly removes an item from the queue - 1pt
   * Handles special cases - 0.5pt
   */
   public E dequeue() {
       /*
       * Remove a node from the list and return it
       */
       return null;
   }
   /*
   * Grading:
   * Correctly shows an item from the queue - 1pt
   * Handles special cases - 0.5pt
   */
   public E peek() {
       /*
       * Show a node from the list
       */
       return null;
   }
  
   private Node front, end;
   private int length;
   public A3Queue() {
       front = end = null;
       length = 0;
   }
   private class Node {
       E value;
       Node next, prev;
       public Node(E v) {
           value = v;
           next = prev = null;
       }
   }
}

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public class A3Driver {
  
   public static void main(String[] args) {
      
       A3DoubleLL list = new A3DoubleLL<>();
       for(int i = 1; i < 10; i++) {
           list.add(i);
       }
       System.out.println("Before Swap");
       System.out.println(list.printList());
       System.out.println(list.printListRev());
       list.swap(4);
       System.out.println("After Swap");
       System.out.println(list.printList() + ":1,2,3,4,6,5,7,8,9,");
       System.out.println(list.printListRev() + ":9,8,7,6,5,4,3,2,1,");
       System.out.println();
      
       System.out.println("Hot Potatoe");
       A3CircleLL hotPotato = new A3CircleLL();
       hotPotato.playGame(5, 3);
       System.out.println("Correct:");
       System.out.println("Removed Player 4\nRemoved Player 3\nRemoved Player 5\nRemoved Player 2\nWinning player is 1");
       System.out.println();
      
       A3Queue queue = new A3Queue<>();
       queue.enqueue(5);
       queue.enqueue(20);
       queue.enqueue(15);
       System.out.println(queue.peek()+":5");
       System.out.println(queue.dequeue()+":5");
       queue.enqueue(25);
       System.out.println(queue.dequeue()+":20");
       System.out.println(queue.dequeue()+":15");

   }
}

Answer 1

If you have any doubts, please give me comment...

/*

* Complete the enqueue(E val) method

* Complete the dequeue() method

* Complete the peek() method

* No other methods/variables should be added/modified

*/

public class A3Queue<E> {

    /*

     * Grading: Correctly adds an item to the queue - 1pt

     */

    public void enqueue(E val) {

        /*

         * Add a node to the list

         */

        Node newItem = new Node(val);

        if (end == null) {

            front = newItem;

            end = front;

        } else {

            end.next = newItem;

            newItem.prev = end;

            end = newItem;

        }

        length++;

    }

    /*

     * Grading: Correctly removes an item from the queue - 1pt Handles special cases

     * - 0.5pt

     */

    public E dequeue() {

        /*

         * Remove a node from the list and return it

         */

        if (front != null) {

            E temp = front.value;

            front = front.next;

            length--;

            return temp;

        }

        return null;

    }

    /*

     * Grading: Correctly shows an item from the queue - 1pt Handles special cases -

     * 0.5pt

     */

    public E peek() {

        /*

         * Show a node from the list

         */

        if (front != null) {

            return front.value;

        }

        return null;

    }

    private Node front, end;

    private int length;

    public A3Queue() {

        front = end = null;

        length = 0;

    }

    private class Node {

        E value;

        Node next, prev;

        public Node(E v) {

            value = v;

            next = prev = null;

        }

    }

}

public class A3Driver {

    public static void main(String[] args) {

        A3Queue<Integer> queue = new A3Queue<>();

        queue.enqueue(5);

        queue.enqueue(20);

        queue.enqueue(15);

        System.out.println(queue.peek() + ":5");

        System.out.println(queue.dequeue() + ":5");

        queue.enqueue(25);

        System.out.println(queue.dequeue() + ":20");

        System.out.println(queue.dequeue() + ":15");

    }

}