#Reverse a string

s = input("Enter a string: ") #Input string from user

print(s[::-1]) #Use slicing to reverse the string. The [::-1] slice notation means to take the string and step backwards, effectively reversing it. The result is printed to the console.

#using for loop

s = input("Enter a string: ") #Input string from user

rev_str = "" #Initialize an empty string to store the reversed string

for char in s:

rev_str = char + rev_str #Prepend each character to the rev_str, effectively reversing the string

print(rev_str) #Print the reversed string to the console

#Using recursion

def rev_string(s): #Definition of a recursive function that takes a string as an argument

if len(s) == 0: #Base case: if the string is empty, return an empty string

return s

else:

return rev_string(s[1:]) + s[0] #Recursive case: call the function on the substring starting from the second character and append the first character at the end

s = input("Enter a string: ") #Input string from user

print(rev_string(s)) #Call the recursive function and print the reversed string to the console

#using built-in function

s = input("Enter a string: ") #Input string from user

print(''.join(reversed(s))) #Use the built-in reversed() function to reverse the string and join the characters back together using ''.join(). The result is printed to the console.

#using stack

s = input("Enter a string: ") #Input string from user

stack = [] #Initialize an empty list to be used as a stack

for char in s: #Loop through each character in the input string

stack.append(char) #Push each character onto the stack

rev_str = "" #Initialize an empty string to store the reversed string

while stack: #While the stack is not empty

rev_str += stack.pop() #Pop characters from the stack and append them to rev_str, effectively reversing the string

print(rev_str) #Print the reversed string to the console

#using list comprehension

s = input("Enter a string: ") #Input string from user

rev_str = ''.join([s[i] for i in range(len(s)-1, -1, -1)]) #Use a list comprehension to create a list of characters in reverse order and join them back together using ''.join(). The result is stored in rev_str.

print(rev_str) #Print the reversed string to the console

#using recursion with slicing

def rev_string(s): #Definition of a recursive function that takes a string as an argument

if len(s) == 0: #Base case: if the string is empty, return an empty string

return s

else:

return rev_string(s[1:]) + s[0] #Recursive case: call the function on the substring starting from the second character and append the first character at the end

s = input("Enter a string: ") #Input string from user

print(rev_string(s)) #Call the recursive function and print the reversed string to the console

#using recursion with slicing and a helper function

def rev_string_helper(s, index): #Definition of a helper function that takes a string and an index as arguments

if index < 0: #Base case: if the index is less than 0, return an empty string

return ""

else:

return s[index] + rev_string_helper(s, index - 1) #Recursive case: append the character at the current index to the result of calling the helper function with the index decremented by 1

def rev_string(s): #Definition of the main function that takes a string as an argument

return rev_string_helper(s, len(s) - 1) #Call the helper function with the string and the index of the last character

s = input("Enter a string: ") #Input string from user

print(rev_string(s)) #Call the main function and print the reversed string to the console

#time complexity of all the above methods is O(n) where n is the length of the input string, as each method processes each character of the string once to reverse it.