质数算法

class Program
{
        static List<int> _PrimeFactos = null;

        static void Main(string[] args)
        {            
            var number = 0;
            string numberString = null;
            do
            {
                Console.WriteLine("Input a range number:");
                numberString = Console.ReadLine();
            } while (!int.TryParse(numberString, out number));

            //Performance Profiler 1
            var watcher = new Stopwatch();
            watcher.Start();
            CalcPrimes1(number);
            Console.WriteLine();
            Console.WriteLine("Algorithm 1: {0}:{1}.{2}", watcher.Elapsed.Minutes, watcher.Elapsed.Seconds,watcher.Elapsed.Milliseconds);
            watcher.Stop();

            //Performance Profiler 2
            Console.WriteLine();
            watcher.Restart();
            CalcPrimes2(number);
            Console.WriteLine();
            Console.WriteLine("Algorithm 2: {0}:{1}.{2}", watcher.Elapsed.Minutes, watcher.Elapsed.Seconds, watcher.Elapsed.Milliseconds);
            watcher.Stop();

            Console.ReadKey();
        }

        static void CalcPrimes1(int number)
        {
            Console.Write("2 ");
            for (var i = 3; i <= number; i += 2)
            {
                if (IsPrime1(i))
                    Console.Write(i + " ");
            }
        }

        static void CalcPrimes2(int number)
        {
            Console.Write("2 ");
            for (var i = 3; i <= number; i += 2)
            {
                if (IsPrime2(i))
                    Console.Write(i + " ");
            }
        }

        static bool IsPrime1(int number)
        {
            if (number == 2)
                return true;
            int squareRoot = Convert.ToInt32(Math.Sqrt(number));
            for (var i = 2; i <= squareRoot; i++)
                if (number % i == 0)
                    return false;
            return true;
        }

        static bool IsPrime2(int number)
        {
            if (_PrimeFactos == null)
            {//init for prime factors
                _PrimeFactos = new List<int>();
                _PrimeFactos.Add(2);
            }
            foreach (var factor in _PrimeFactos)
            {
                if (number % factor == 0)
                    return false;
            }
            if (!_PrimeFactos.Contains(number))
                _PrimeFactos.Add(number);
            return true;
        }
}