OJ Board

I think that there is a mistake in the second image. The subscript of the last number should be i, x(i-1) and not i, x(i). I hope some admin notices this and fix the mistake. I don't know where else to report this so I am posting this here.

The whole image is dirty and small, magnifying doesn't help. Guessing the problem took me more time than solving it on the contest.

I'm getting TLE. My aproach is simply calculating sum R times. Can somebody give some hints plz? I don't know another solution for this problem.

Try to convert the problem into result = a^r; Find that in ln(r).

Thanks lyhung. You said to convert problem to A^r, so I tried to think different and I think I can use n*n matrix A that contains 1 & 0 (for given sum rules), and multiply A^r into original numbers, but I don't know how to compute A^r efficiently (instead of multiplying A into itself r times). Plz give me some more hint. Maybe I haven't understood your previous hint at all .
BTW, sorry for my very bad English

Finally accepted with time 0.100 . Special thanX to lyhung