Question

In Java: Initiate empty queue of strings and recreate .isempty, .size, .dequeue, .enqueue methods.

//You may not use the original methods of the stack api to answer.

import java.util.NoSuchElementException;

import edu.princeton.cs.algs4.Stack;

public class StringQueue {
   //You may NOT add any more fields to this class.
   private Stack stack1;
   private Stack stack2;

   /**
   * Initializes an empty queue.
   */
   public StringQueue() {

//TODO
   }

   /**
   * Returns true if this queue is empty.
   *
   * @return {@code true} if this queue is empty; {@code false} otherwise
   */
   public boolean isEmpty() {
       //TODO
   }

   /**
   * Returns the number of items in this queue.
   *
   * @return the number of items in this queue
   */
   public int size() {
       // TODO
   }

   /**
   * Adds the item to this queue.
   *
   * @param item the item to add
   */
   public void enqueue(String item) {
       // TODO
   }

   /**
   * Removes and returns the item on this queue that was least recently added.
   *
   * @return the item on this queue that was least recently added
   * @throws NoSuchElementException if the queue is empty
   */
   public String dequeue() throws NoSuchElementException {
       // TODO
   }
}

Answer 1

Solution:

import java.util.NoSuchElementException;

import edu.princeton.cs.algs4.Stack;

public class StringQueue {
//You may NOT add any more fields to this class.
private Stack stack1;
private Stack stack2;

/**
* Initializes an empty queue.
*/
public StringQueue() {

   stack1 = new Stack();

stack2 = new Stack();

  
}

/**
* Returns true if this queue is empty.
*
* @return {@code true} if this queue is empty; {@code false} otherwise
*/
public boolean isEmpty() {
return stack1.isEmpty();

}

/**
* Returns the number of items in this queue.
*
* @return the number of items in this queue
*/
public int size() {
return stack1.size() + stack2.size();

}

/**
* Adds the item to this queue.
*
* @param item the item to add
*/
public void enqueue(String item) {

if(item == null || item == "" || item == " ")

return;

    stack1.push(item);

}
  

/**
* Removes and returns the item on this queue that was least recently added.
*
* @return the item on this queue that was least recently added
* @throws NoSuchElementException if the queue is empty
*/
  public String dequeue() throws NoSuchElementException {
  
if(stack2.isEmpty())

{

while(!stack1.isEmpty())

{

stack2.push(stack1.pop());

}

}

String popped = stack2.pop();

if(stack1.isEmpty())

{

while(!stack2.isEmpty())

{ stack1.push(stack2.pop());

}

}

return popped;

}
}