Hi all !

Please don't take this the wrong way - I don't want to be offensive or anything, but I've seen many solutions here which employ a method that is, in my humble opinion, highly not recommended: creating a huge array of 100000 ints and simply generating the whole lot in O(N) time - which is both time and memory-consuming. Due to the excessively permissive limits, these solutions actually work, but I believe this isn't how a good coder should solve the problem. Instead, all I can tell you is that a solution exists that needs very little memory (no arrays) and works in O(log N) time.

could you please tell me as a hint??
Is it require a math solution ??
I was puzzled by this problem for a whole day.
thanks in advance.