Friday, 14 January 2022

Python program to implement stack operations using

A Stack is linear structure where insertions and deletions are done at one end called top of the stack. The principle of stack is LIFO, the lastly inserted element is deleted first.

Here are two implementations of stack using arrays. The first one uses arrays standard methods: append() and pop() to implement and the second one uses user defined functions.

1. Using Python array standard methods

# Python program to
# demonstrate stack implementation
# using list

stack = []

# append() function to push
# element in the stack
stack.append('10')
stack.append('20')
stack.append('30')

print('Initial stack')
print(stack)

# pop() function to pop
# element from stack in
# LIFO order
print('\nElements popped from stack:')
print(stack.pop())
print(stack.pop())
print(stack.pop())

print('\nStack after elements are popped:')
print(stack)


Output 

Initial stack
['10', '20', '30']

Elements popped from stack:
30
20
10

Stack after elements are popped:
[]

2. Using user defined functions 

# Creating a stack
def create():
    stack = []
    return stack

# Creating an empty stack
def is_empty(stack):
    return len(stack) == 0

# Adding items into the stack
def push(stack, item):
    stack.append(item)
    print("pushed item: " + item)

# Removing an element from the stack
def pop(stack):
    if (is_empty(stack)):
        {
        print("stack is empty")
        }
    return stack.pop()


stack = create()
push(stack, str(1)) #converting number to string using str()
push(stack, str(2))
push(stack, str(3))
push(stack, str(4))
print("-----------------------")
print("popped item: " + pop(stack))
print("popped item: " + pop(stack))
print("popped item: " + pop(stack))
print("popped item: " + pop(stack))
print("---------------------")
print("stack after popping an element: " + str(stack))


Output

pushed item: 1
pushed item: 2
pushed item: 3
pushed item: 4
-----------------------
popped item: 4
popped item: 3
popped item: 2
popped item: 1
---------------------
stack after popping an element: []

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