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;
       }
   }
}

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

public class A3Driver {
  
   public static void main(String[] args) {
      
  
       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

/*
 * 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 n = new Node(val);
        if (front == null) {
            front = end = n;
        } else {
            end.next = n;
            end = n;
        }
    }

    /*
     * 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
         */
        E result = front.value;
        front = front.next;
        return result;
    }

    /*
     * Grading:
     * Correctly shows an item from the queue - 1pt
     * Handles special cases - 0.5pt
     */
    public E peek() {
        /*
         * Show a node from the list
         */
        return front.value;
    }

    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;
        }
    }
}