I solved another problem: Palindrome chain length

This is a calculation problem about palindromes. A palindrome is a string that, when split in the middle, has left and right sides that are symmetric in reverse order. For example, “あいういあ” is a palindrome, while “あいうえお” is not. The same applies to numbers: 5, 44, 171, 4884 are palindromes, while 43, 194, 4773 are not.

This problem asks, for a given number, how many times a specific calculation must be performed to make it a palindrome. The calculation is: reverse the digits of the number and add it to the original number.

For example, if 87 is given, it becomes a palindrome after 4 calculations, so the return value is 4.

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

The tricky part is how to reverse the digits of a number. After some research, I found it surprisingly easy, and it can be done in one line. Reverse string in Python

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str(n)       # Convert number to string
str(n)[::-1] # Convert number to string and reverse it

This way, you can extract elements from the end of the string to the beginning one by one.

Here is my answer to the problem:

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def palindrome_chain_length(n):
    cnt=0
    while str(n) != str(n)[::-1] :
        cnt += 1
        n   += int(str(n)[::-1])
    return cnt

Wow, that’s convenient! Now I can sleep well tonight~