Do you mean your code works fine in that case and fails in another? In which one, what's the input and what does your code return? If you post your code, follow this guide: https://docs.codewars.com/training/troubleshooting/#post-discourse

The highest or lowest element respectively is a single element at each edge, even if there are more than one with the same value.

It's explained in the description.

And how many 1s has 256 in binary? You have to return the next higher number with the same amount of 1s in its binary form. 128 has 1 too.