At least it can't be used for cheating

First of all thank you for your reply.

How do you know this?

Like I had no Idea this was the case and was stuck for like half a day.

Yeah that's what we have to find, whether the number is of the form x^3 OR x^3+ 4 (for any positive x)

We have to say yes if it's of the form x^3 And no if it's of the form x^3+4

I don't know what you mean

Okay, I think I get it and I understood the i,j you used were different basically Si,j means jth character of Si in what you said right.

So basically we trace back to either if i becomes 0 or j becomes 1.

If j becomes 1 find that element then go to Si,j using order like just increment by 1(A->B->c->A) like that.

If i becomes 0 then we just find that character then increase in order by 1 to get to Si,j.

And if it's divisible by 2 it's second character of replacement and if not, it's first replacement.

What's the difficulty according to you?

I'm sorry, I get that we can trace back so say str='A' and I want to find i=4,j=2, I trace back to i=3,j=1 So now I have to find S 3,1 after that I am a bit lost, can you please explain a bit.

Thanks again.

Hi, thanks for your reply.

I am trying to understand your method(I am a bit slow).

What would you say is the difficulty of this problem?