if words is an "", then *(tmp++) = *words; *tmp = 0; this will set 2 zeros.

If each individual test gave the minimum required amount of memory for letters, then this solution, on empty words, would have exited and written out of memory limits for letters.

gcc -m32 ? (solution not suitable for 32 bit architectures?)

Maybe the '1' should be extended to 'uint64_t' instead of 'long'?

Functions "findIndex" and "rotate" are non-standard and also not available in the viewable code. So how can everyone come to this solution?

I tried to avoid memory allocation. And also build the array of primes only once for all tests.

Having looked at other people's solutions, I realized that you could think about replacing
prime_numbers[i] <= n_div_2
by
prime_numbers[i] <= n_sqrt
and then change the logic of the calculation (I admit, this part of the solution I did not work out very well).

And also it is worth finding a threshold for the input number, above which my solution will contain fewer steps. Otherwise, use a simple solution.

It was interesting for me to decide correctly (as far as I understand it), although it seems to me that it is a little higher than 7kyu.

Hopefully someone can benefit from this.

Good luck to everyone reading this!

@hobovsky - Thank you. (you can explain, I appreciate it.)

I take everything personally, too close to my heart. I am often told about this. ("This cruel world") Sorry.
Or do you need a different genre of response? Continuation? Action?

Yes, I understand this.
(You offend me.)
Have a nice day for me! =)

I know this, but I have no way to fix it.

Yes, a mistake.

I have already fixed this in the next submit.

Obviously so - unsigned char arr['{'];

If you need to explain something in detail for you, write to me in a personal.