Question 5 - Past Year - 2 Mark Questions - Chapter 3 - Stacks

Write a Python program to check if a string is a palindrome or not.

Answer:

A palindrome is a sequence of characters that read the same backwards as forwards. 

Example: level, madam, refer, etc.

To check if a string is palindrome:

• First, insert all characters of the string into a stack. 
• Then, using a for loop, keep popping the elements of the stack and compare them with corresponding characters of the string from the beginning. 
• If at any point, there is a mismatch, then the string is not a palindrome.

Code:

def push(stack,x):

stack.append(x)

return

def pop_stack(stack):

if len(stack)==0:

return

else:

c=stack.pop()

return c

def compare(string,stack):

for i in range(len(string)):

if string[i]!= pop_stack(stack):

return False

return True

stack=[]

input_string=input("Enter a string: ")

for a in input_string:

push(stack,a)

cmp=compare(input_string,stack)

if cmp:

print("Entered string is a palindrome")

else:

print("Entered string is not a palindrome")

Output:

Enter a string: madam

Entered string is a palindrome