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Python Program to Check If a Number is Palindrome or Not

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Palindrome

Python programs to check if a number is a palindrome or not have been shown here. For example, 1221 is a palindrome because we get the same number irrespective of the direction (left to right or right to left) of reading. But 1234 is not a palindrome as we get 4321 if we read it from right to left.

The algorithm, time complexity and pseudocode of the program have been shown below.






1. Algorithm to check if a number is a palindrome or not


1. Take a number n as input.

2. Copy value of n to another variable say m i.e. m = n.

3. Initialize a variable to 0 say reverse = 0.

4. Perform r = n % 10.

5. Perform reverse = reverse * 10 + r.

6. Perform n = n / 10

7. If n = 0 go to step 8 else go to step 3.

8. Check If reverse == m

9. If step 8 is true then n is palindrome else n is not palindrome.




2. Pseudocode to check if a number is a palindrome or not


Input : A number $n$

Output : Palindrome or Not Palindrome

1. Procedure checkPalindrome($n$):

2. $reverse \leftarrow 0$

3. $m \leftarrow n$

4. Repeat until $n \neq 0$

5. $reverse \leftarrow reverse * 10 + (n \mod 10)$

6. $n \leftarrow n / 10$

7. If $reverse == m$:

8. Return "Palindrome"

9. Else:

10. Return "Not Palindrome"

11. End Procedure





3. Time complexity to check if a number is a palindrome or not


Time Complexity: O(log(n))

Where n is the input number.





4. Python Program & output to check if a number is a palindrome or not using iteration

Code has been copied
# ***************************************
#        alphabetacoder.com
# Python program to check if a number is
# a palindrome or not using iteration
# ***************************************

# take input of the number
n = int(input("Enter the number = "))

# initialize
m = n
revnum = 0

# find the reverse
while n != 0:
    # extract the unit digit
    r = n % 10
    # store the reverse number
    # give appropriate positional value
    # of each digit
    revnum = revnum * 10 + r
    # divide the number by 10
    n = n // 10

# check for palindrome
if m == revnum:
    print(m, "is a palindrome!")
else:
    print(m, "is not a palindrome!")

Output

Enter the number = 50505

50505 is a palindrome!





5. Python Program & output to check if a number is a palindrome or not using recursion

Code has been copied
# ***************************************
#        alphabetacoder.com
# Python program to check if a number is
# a palindrome or not using recursion
# ***************************************

# recursive function to check if
# a number is a palindrome or not
def check_palindrome(n, num, rev):
    if n == 0:
        # if reverse is same as original
        if num == rev:
            return 1
        else:
            return 0
    else:
        return check_palindrome(n // 10, num, (rev * 10 + n % 10))


def main():
    # take input of the number
    num = int(input("Enter the number = "))

    # check for palindrome
    # by calling the function
    # If the function returns 1,
    # then the number is palindrome
    # else the number is not palindrome
    if check_palindrome(num, num, 0) == 1:
        print(num, "is a palindrome!")
    else:
        print(num, "is not a palindrome!")


# driver code
main()

Output

Enter the number = 61916

61916 is a palindrome!





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