In class, we discussed the abstract data structure Stack. A stack is a collection of items where items are added to and removed from the top (LIFO). Use the Node class (an object with a data field and a pointer to the next element) to implement the stack data structure with the following operations:

Stack() creates a new stack that is empty. It needs no parameters and returns nothing

push(item) adds a new Node with value=item to the top of the stack. It needs the item and returns nothing.

pop() removes the top Node from the stack. It needs no parameters and returns the value of the Node removed from the stack. Modifies the stack.

peek() returns the value of the top Node from the stack but does not remove it. It needs no parameters. The stack is not modified.

isEmpty() tests to see whether the stack is empty. It needs no parameters and returns a boolean value.

len() returns the number of items on the stack. It needs no parameters and returns an integer. (You can add count in the Stacks constructor)

EXAMPLE

>>> x=Stack()

>>> x.pop()

'Stack is empty'

>>> x.push(2)

>>> x.push(4)

>>> x.push(6)

>>> x Top:Node(6)

Stack: 6 4 2

>>> x.pop()

6

>>> x Top:Node(4)

Stack: 4 2

>>> len(x)

2

>>> x.isEmpty()

False

>>> x.push(15)

>>> x Top:Node(15)

Stack: 15 4 2

>>> x.peek()

15

>>> x Top:Node(15)

Stack: 15 4 2

NOTE: To grade this assignment, the grading script will perform a series of mixed stack operations and compare the final status of your stack. Verify that all your methods work correctly when mixed together. Tips: - Make sure you update the top pointer according to the operation performed - Starter code contains the special methods __str__ and __repr__, use them to ensure the stack operations are updating the elements in the stack correctly - When a method is asking to return the value of a node, make sure you are returning node.value and not a Node object

Given below is the starter code: Please write the code in python 3

class Node: def __init__(self, value): self.value = value self.next = None def __str__(self): return "Node({})".format(self.value)

__repr__ = __str__

class Stack: ''' Creates an empty Stack with support for push and pop operations >>> x=Stack() >>> x.pop() 'Stack is empty' >>> x.push(2) >>> x.push(4) >>> x.push(6) >>> x Top:Node(6) Stack: 6 4 2 >>> x.pop() 6 >>> x Top:Node(4) Stack: 4 2 >>> len(x) 2 >>> x.peek() 4 ''' def __init__(self): self.top = None def __str__(self): temp=self.top out=[] while temp: out.append(str(temp.value)) temp=temp.next out=' '.join(out) return ('Top:{} Stack: {}'.format(self.top,out))

__repr__=__str__ def isEmpty(self):

def __len__(self): def peek(self):

def push(self,value):

def pop(self):