We cannot know what you're doing wrong without knowing your code, sorry.

"For this Kata you need to write a function that takes a string of characters and returns the length, as an integer value, of longest alphanumeric palindrome that could be made by rearranging the characters."

I think this more clearly and concisely explains the goal.

The emphasized part is saying that the final palindrome should never have a letter appearing more in it than in the original string.

So you can't do aaabb -> aabbaa, because that would turn a's, count from 3 to 4. You could do aaabb -> abba though, as 2 <= 3.

I do agree that the description is quite lacking, but as this doesn't seem like a suggestion, I'm marking as resolved.

Review the definition of factor: https://www.britannica.com/science/factor-mathematics

You're thinking about prime factors, and that's another thing.

1 is not a prime number. Therefore 1 cannot be considered a "factor", but 1 is a divisor of the base. Consider renaming the kata and objectives.

Since z/Z is the last letter to find, we only have to index to m/M.

This version of kata does not have inputs with adjacent +.

1. It is unfortunate that the kata's requirement's changed to include pieces with holes. My original solution would have sufficed.
2. "There are no borders touching each others." Would the following shape be allowed (python)?

"\n".join(["++--+","++--+","| |","+---+"])

This has been changed by Voile. Now the function expects long long and it's ok.