Hi, please don't attempt to do 1kyu katas unless you're confident in your skills, 1kyu katas are the most difficult ones. You should be doing 8kyu katas instead.

In any case, this is your code's issue, you can't create a array with size greater than 2^32 - 1. And this approach wouldn't work anyway ;-)

How can you tell that your code returns a correct result? Because it does not.

Did you try to debug your code in a step-through debugger and see what happens wrong, and when? Hint: the problem is related to the line j += " ".