To avoid code like: (double) 1 / ((double) n * (double) n);

You can simply write 1./(n*n). The dot behind the 1 will turn its type to double, and divison between double and int gives double.

I'd recommend storing the size of the initial array to avoid recalculating it every time we drop 1 element.

Nice kata idea and nice solution you implemented. Cheers

Nearly identical to my own solution, a suggestion for you though, try using move() for the result = temp for better eficiency.

Instead of calling lowercased() on each character, you can call it only once on the string itself, making it more efficient. Cheers!