Question

ii. (30) A Stack is a container commonly used to provide a way to keep organized so that the last one pushed' onto the top of the stack is thth one 'popped (removed)- so stacks are called "last-in-first-out". on top of the stack is visible, but after removing the top item, t pushed item is visible, since it is back on top. The following Python co is a recursive definition of the class Stack. Read the code, and answer te Only the the previously questions which follow: class Stack (object) def init. (self): self.top = None self.restNone def push(self, item): if self.topNone: self.rest Stack) self.rest.push(self.top) self.top item else: self .top item def pop(self): if self.top None: return None else: item self.top self.top = self.rest.pop ( ) return item a. Identify, by circling and labeling, which parts of the method defi- nitions for push and pop are base case and recursive case b. Draw a class symbol diagram for Stack, giving all attributes and methods. For each attribute, specify its type. (Assume all items pushed and popped are integers.) c. Explain how this class definition is both structurally and function- ally recursive. d. A stack is empty if either nothing has yet been pushed onto it or everything that was pushed has been popped off the stack. Write a method enpty that returns True exactly when the stack is empty.

Answer 1

Solution:

a)

for push:

Base case:

if self.top==None

Recursive case:

the else part where

self.rest.push(self.push)

b)

stack cl noa Pope, to res ddo em teu

c)

Because push and pop are structurally defined in the class and within these functions, we can see that they are calling themselves recursively.

d)

def emptyStack:

if self.top==None

return true

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