arrrrggggg this is smart and so obvious!! I totally forgot about gsub.

I agree :)

Test cases include paired arrays of differing lengths for the Java version.

Thanks!

Think this should be harder than 7 kyu.

Please don't post issues without concrete elements. Read this: https://docs.codewars.com/training/troubleshooting/

In my code there is an error but it's not actually in my code, I think it's in your solutions.

In the instructions please add a note that the arrays are of the same length.

I went down a rabbit hole playing with different lengths trying to figure out that assumption. The instructions note that for the C language, but it appears to hold true generally.

Thanks!

Nice use of composition.

You're right, but it's more readable imo. It depends on people I guess.

This doesn't need the () % is ahead of - in order of operations

'return s1' ?