O(n)比O(nlogn)需要更多的时间

I was trying this problem on spoj. First of all I came up with a sort of trivial o(blogb) algorithm(refer the problem for whats b).But since the author of the problem mentioned the constraints as b belongs to [0,10^7] i was not convinced if it would pass.Anyways out of shear belief I coded it as follows problem on spoj. First of all