Project Euler – Problem 3

Problem 3 showcases the use of functions, a while loop, and a call to the Math library.

using System;

class Program
{
    // Function that checks whether a number is prime
    static bool isPrime(long n)
    {
        int i;

        for (i=2;i<=Math.Sqrt(n);i++)
        {
            if (n%i==0) return false;
        }
        return true;

    }

    // Function that returns the next prime after a given number
    static long nextPrime(long n)
    {
        n++;

        while (!isPrime (n))
        {
            n++;
        }

        return n;

    }

    // Function that returns the largest prime factor of a number
    static long LargestPrimeFactor(long n)
    {
        long i=2;

        while (!isPrime (n))
        {
            if (n%i==0){
                n = n/i;
            } else {
                i=nextPrime(i);
            }
        }

        return n;
    }

    static void Main(string[] args)
    {
        Console.WriteLine("{0}", LargestPrimeFactor(600851475143));

        Console.ReadKey();
    }
}