I need an optimal algorithm to find the largest divisor of a number N. Preferably in C++ or C#

Question

I am currently using the following code but its very slow for large numbers

        static int divisor(int number)
        {
            int i;
                    


        

Answer 1

A solution if you know the smallest divisor is to apply the following formula:

largest_d = N - N % smallest_d

where N is the number whose largest divisor you're looking for.

def largest_divisor(N, smallest_divisor):
   return N - N % smallest_divisor

This code with a random big number (N = 94e15) and a random big divisor (divisor = 21e3) finished running the program in Python in 0.000740051269531 s.

Hope this helps.