Question

Implement the EasyStack interface with the MyStack class. You can use either a linked list or a dynamic array to implement the data structure.

A stack is a specialised form of list in which you can only get and remove the element most recently added to the stack.

The class should be able to work with the following code:

EasyStack stack = new MyStack();

NB: You cannot import anything from the standard library for this task. The data structure must be of your own creation, not a modified form of a pre-existing class.

public interface EasyStack {
  
   /**
   * Returns true if the stack is empty, else false.
   *
   * @return   whether the stack is empty
   */
   public boolean empty();
  
   /**
   * Returns the most recently added array, null if empty.
   *
   * @return   the most recently added array
   */
   public int[] peek();
  
   /**
   * Returns and removes the most recently added array, null if empty.
   *
   * @return   the most recently added array
   */
   public int[] pop();
  
   /**
   * Appends the array to the end of the stack. Does nothing if the array is empty or null.
   *
   * @param arr   the array to be added
   */
   public void push(int[] arr);
  
   /**
   * Finds the distance from the end of the stack the closest array with equal contents.
   * Returns -1 if the array is not present.
   *
   * @return   the distance from end
   */
   public int distance(int[] arr);
  
   /**
   * Returns the size of the stack
   *
   * @return   the size of the stack
   */
   public int size();
  
   /**
   * Returns true if the contents of the stack equal the contents of another stack, else false
   *
   * @return   whether the two stacks are equal
   */
   public boolean equals(EasyStack stack);
}

Answer 1

public interface EasyStack {
/**
* Returns true if the stack is empty, else false.
*
* @return whether the stack is empty
*/
public boolean empty();
  
/**
* Returns the most recently added array, null if empty.
*
* @return the most recently added array
*/
public int[] peek();
  
/**
* Returns and removes the most recently added array, null if empty.
*
* @return the most recently added array
*/
public int[] pop();
  
/**
* Appends the array to the end of the stack. Does nothing if the array is empty or null.
*
* @param arr the array to be added
*/
public void push(int[] arr);
  
/**
* Finds the distance from the end of the stack the closest array with equal contents.
* Returns -1 if the array is not present.
*
* @return the distance from end
*/
public int distance(int[] arr);
  
/**
* Returns the size of the stack
*
* @return the size of the stack
*/
public int size();
  
/**
* Returns true if the contents of the stack equal the contents of another stack, else false
*
* @return whether the two stacks are equal
*/
public boolean equals(EasyStack stack);
}

class MyStack implements EasyStack
{
   private class Node
   {
       int array[];
       Node next;
       Node prev;
      
       Node(int arr[])
       {
           array = new int[arr.length];
           for(int i=0; i<array.length; i++)
           {
               array[i] = arr[i];
           }
           next = null;
           prev = null;
       }
      
       public boolean equals(Node node)
       {
           if(array.length!=node.array.length)
               return false;
           for(int i=0; i<array.length; i++)
           {
               if(array[i]!=node.array[i])
                   return false;
           }
           return true;
       }
   }
  
   private Node first;
   private int size;
  
   public MyStack()
   {
       first = null;
       size = 0;
   }
     
   /**
* Returns true if the stack is empty, else false.
*
* @return whether the stack is empty
*/
public boolean empty()
{
        return first==null;
}
  
/**
* Returns the most recently added array, null if empty.
*
* @return the most recently added array
*/
public int[] peek()
{
        if(empty()) return null;
        return first.array;
}
  
/**
* Returns and removes the most recently added array, null if empty.
*
* @return the most recently added array
*/
public int[] pop()
{
        if(empty()) return null;
        int arr[] = first.array;
        first = first.next;
        first.prev = null;
        size--;
       return arr;
}
  
/**
* Appends the array to the end of the stack. Does nothing if the array is empty or null.
*
* @param arr the array to be added
*/
public void push(int[] arr)
{
        Node newnode = new Node(arr);
        newnode.next = first;
        newnode.prev = null;
        first = newnode;
        size++;
}
  
/**
* Finds the distance from the end of the stack the closest array with equal contents.
* Returns -1 if the array is not present.
*
* @return the distance from end
*/
public int distance(int[] arr)
{
        Node node = first;
        int len = node.array.length;
        int dis = 0;
        while(node!=null)
        {
            node = node.next;
            dis++;
            if(len==node.array.length)
                break;
        }
        if(node==null)
            return -1;
        return dis;
}
  
/**
* Returns the size of the stack
*
* @return the size of the stack
*/
public int size()
{
        return size;
}
  
/**
* Returns true if the contents of the stack equal the contents of another stack, else false
*
* @return whether the two stacks are equal
*/
public boolean equals(EasyStack stack)
{
        if(stack instanceof MyStack){
       
        Node node1 = first;
        MyStack stk = (MyStack)stack;
        Node node2 = stk.first;
        while(node1!=null && node2!=null)
        {
            if(!node1.equals(node2))
                break;
            node1 = node1.next;
            node2 = node2.next;
        }
        if(node1==null && node2==null)
            return true;
        return false;
        }
        return false;
}
}

class Driver
{
   public static void main (String[] args)
   {
       EasyStack stack = new MyStack();
   }
}