palindrome_chain_length.py

"""
Number is a palindrome if it is equal to the number with digits in reversed order.
For example, 5, 44, 171, 4884 are palindromes and 43, 194, 4773 are not palindromes.

Write a method palindrome_chain_length which takes a positive number and
returns the number of special steps needed to obtain a palindrome.
The special step is: "reverse the digits, and add to the original number".
If the resulting number is not a palindrome,
repeat the procedure with the sum until the resulting number is a palindrome.

If the input number is already a palindrome, the number of steps is 0.

Input will always be a positive integer.

For example, start with 87:

87 + 78 = 165; 165 + 561 = 726; 726 + 627 = 1353; 1353 + 3531 = 4884

4884 is a palindrome and we needed 4 steps to obtain it, so palindrome_chain_length(87) == 4

"""


def palindrome_chain_length(n):
    # parameter n is a positive integer
    # your function should return the number of steps
    rev_n = int(str(n)[::-1])
    step = 0

    if n == rev_n:
        return step

    while n != rev_n:
        n += rev_n
        rev_n = int(str(n)[::-1])
        step += 1

    return step


from unittest import TestCase


class TestPalindromeChain(TestCase):
    def test_palindrome_chain_length(self):
        self.assertEquals(4, palindrome_chain_length(87))