Question

Instructions:

SLLStack (12 pts)

● Using the two properties below, implement the stack

interface using the SLLNode class from Lab 2:

○ top_node → SLLNode object or None

○ size → int, keep track of stack size

● Implement the push( ), pop( ), top( ) methods

● Use SLLNode methods:

get_item( ), set_item( ), get_next( ), set_next( )

● (5 pts) In push(item):

○ Create new SLLNode with item

○ Add new node before top node

○ Update top_node and size properties

● (5 pts) In pop( ):

○ If empty, raise Exception('Empty stack: cannot pop')

○ Remove top node and return its item

○ Remove any links from old top node

○ Update top_node and size properties

● (2 pts) In top( ):

○ If empty, raise Exception('Empty stack: no top')

○ Return top node’s item

Code:

class SLLStack:
   def __init__(self):
       # NOTE: DO NOT EDIT THIS CODE
       # constructor: set properties top_node, size
       self.top_node = None
       self.size = 0

   def __repr__(self):
       # NOTE: DO NOT EDIT THIS CODE
       # string representation of SLLStack object
       display = []
       node = self.top_node
       while node != None:
           display.append(str(node.get_item()))
           node = node.get_next()
       display = ', '.join(display)
       return 'top [' + display + ']'

   def is_empty(self):
       # NOTE: DO NOT EDIT THIS CODE
       # check if stack is empty
       return self.size == 0

   def push(self,item):
       # TODO: Write your code here...
       # TODO: add new node (with item) before top_node
       # TODO: update top_node and size properties

       pass # TODO: remove this line

   def pop(self):
       # TODO: Write your code here...
       # TODO: if empty, raise Exception('Empty stack: cannot pop')
       # TODO: remove top node and return its item
       # TODO: remove any links from old top_node (Hint: set to None)
       # TODO: update top_node and size properties
  
       pass # TODO: remove this line

   def top(self):
       # TODO: Write your code here...
       # TODO: if empty, raise Exception('Empty stack: no top')
       # TODO: return top_node's item

       pass # TODO: remove this line

Answer 1

ANSWER:

• I have provided the properly commented code in both text and image format so you can easily copy the code as well as check for correct indentation.
• I have provided the output image of the code so you can easily cross-check for the correct output of the code.
• Have a nice and healthy day!!

CODE TEXT

# sample class SLLNode, as not provided in question
class SLLNode:
def __init__(self,item):
# constructor: set properties item, next_node
self.item = item
self.next = None
  
# method get_item()
def get_item(self):
# return item value
return self.item
  
# method set_item()
def set_item(self,item):
# set item value
self.item = item
  
# method get_next()
def get_next(self):
# return next node
return self.next
  
# method set_next():
def set_next(self,node):
# set next value
self.next = node

# class SLLStack
class SLLStack:
def __init__(self):
# NOTE: DO NOT EDIT THIS CODE
# constructor: set properties top_node, size
self.top_node = None
self.size = 0
  
def __repr__(self):
# NOTE: DO NOT EDIT THIS CODE
# string representation of SLLStack object
display = []
node = self.top_node
while node != None:
display.append(str(node.get_item()))
node = node.get_next()
display = ', '.join(display)
return 'top [' + display + ']'
  
  
def is_empty(self):
# NOTE: DO NOT EDIT THIS CODE
# check if stack is empty
return self.size == 0
  
def push(self,item):
# TODO: Write your code here...
# TODO: add new node (with item) before top_node
# new node, SLLNode object with value item
node = SLLNode(item)
# seting next value of node to top_node, using set_next method
node.set_next(self.top_node)
  
# TODO: update top_node and size properties
# updating top_node to node
self.top_node = node
# updating size, by incrementing by 1
self.size += 1
  
def pop(self):
# TODO: Write your code here...
# TODO: if empty, raise Exception('Empty stack: cannot pop')
if self.size == 0:
raise Exception('Empty stack: cannot pop')
  
# TODO: remove top node and return its item
# defining next_node and assigning it next node to top node
# using get_next() method
next_node = self.top_node.get_next()
# fetching value from top_node using get_item method
top_value = self.top_node.get_item()
  
# TODO: remove any links from old top_node (Hint: set to None)
# assigning next of top_node to none, using set_next
self.top_node.set_next(None)
  
# TODO: update top_node and size properties
# updating top_node to next_node
self.top_node = next_node
# decrementing size by 1
self.size -= 1
  
# returning top_value
return top_value
  
def top(self):
# TODO: Write your code here...
# TODO: if empty, raise Exception('Empty stack: no top')
if self.size == 0:
raise Exception('Empty stack: no top')
  
# TODO: return top_node's item
# using get_item method
return self.top_node.get_item()
  
## example
# defining stack
stack = SLLStack()
# pushing values 0 to 9 in stack
for i in range(10):
stack.push(i)
  
# displaying stack
print("Initial stack:",stack)

# displaying top value
print("Top value:",stack.top())

# displaying pop value and left stack
pop = stack.pop()
print("Pop value:",pop,",Left stack:",stack)

CODE IMAGE

OUTPUT IMAGE