1+ import os
2+ 3+ 4+ class _Node :
5+ '''
6+ Creates a Node with two fields:
7+ 1. element (accesed using ._element)
8+ 2. link (accesed using ._link)
9+ '''
10+ __slots__ = '_element' , '_link'
11+ 12+ def __init__ (self , element , link ):
13+ '''
14+ Initialses _element and _link with element and link respectively.
15+ '''
16+ self ._element = element
17+ self ._link = link
18+ 19+ 20+ class StackLL :
21+ '''
22+ Consists of member funtions to perform different
23+ operations on the linked list.
24+ '''
25+ 26+ def __init__ (self ):
27+ '''
28+ Initialses head, tail and size with None, None and 0 respectively.
29+ '''
30+ self ._head = None
31+ self ._tail = None
32+ self ._size = 0
33+ 34+ def __len__ (self ):
35+ '''
36+ Returns length of stack.
37+ '''
38+ return self ._size
39+ 40+ def isempty (self ):
41+ '''
42+ Returns True if stack is empty, otherwise False.
43+ '''
44+ return self ._size == 0
45+ 46+ def push (self , e ):
47+ '''
48+ Pushes the passed element at the beginning of the linked list.
49+ That means, on the top of our stack.
50+ '''
51+ newest = _Node (e , None )
52+ 53+ if self .isempty ():
54+ self ._head = newest
55+ self ._tail = newest
56+ else :
57+ newest ._link = self ._head
58+ self ._head = newest
59+ self ._size += 1
60+ 61+ def pop (self ):
62+ '''
63+ Removes element from the beginning of the linked list.
64+ That means, pops element that is on the top.
65+ Returns the removed element.
66+ '''
67+ if self .isempty ():
68+ print ("Stack is Empty. Cannot perform Pop operation." )
69+ return
70+ 71+ e = self ._head ._element
72+ self ._head = self ._head ._link
73+ self ._size = self ._size - 1
74+ 75+ if self .isempty ():
76+ self ._tail = None
77+ 78+ return e
79+ 80+ def top (self ):
81+ '''
82+ Peeks at the element on the top of the stack.
83+ '''
84+ if self .isempty ():
85+ print ("Stack is Empty. Cannot perform Pop operation." )
86+ return
87+ 88+ e = self ._head ._element
89+ return e
90+ 91+ def display (self ):
92+ '''
93+ Utility function to display the Stack.
94+ '''
95+ if self .isempty () == 0 :
96+ p = self ._head
97+ while p :
98+ print (p ._element )
99+ p = p ._link
100+ else :
101+ print ("Empty" )
102+ 103+ ###############################################################################
104+ 105+ def options ():
106+ '''
107+ Prints Menu for operations
108+ '''
109+ options_list = ['Push' , 'Pop' , 'Top' ,
110+ 'Display Stack' , 'Exit' ]
111+ 112+ print ("MENU" )
113+ for i , option in enumerate (options_list ):
114+ print (f'{ i + 1 } { option } )
115+ 116+ choice = int (input ("Enter choice: " ))
117+ return choice
118+ 119+ 120+ def switch_case (choice ):
121+ '''
122+ Switch Case for operations
123+ '''
124+ os .system ('cls' )
125+ if choice == 1 :
126+ elem = int (input ("Enter Item: " ))
127+ S .push (elem )
128+ 129+ elif choice == 2 :
130+ print ('Popped item is: ' , S .pop ())
131+ 132+ elif choice == 3 :
133+ print ("Item on top is: " , S .top ())
134+ 135+ elif choice == 4 :
136+ print ("Stack:" )
137+ S .display ()
138+ print ("\n " )
139+ 140+ elif choice == 5 :
141+ import sys
142+ sys .exit ()
143+ 144+ ###############################################################################
145+ 146+ 147+ S = StackLL ()
148+ while True :
149+ choice = options ()
150+ switch_case (choice )
0 commit comments