using System;

using System.Diagnostics;

using System.Linq;

using System.Numerics;

​

namespace nasdaq

{

    public class Program

    {

        public static void Main(string[] args)

        {

            var prod = Product(5, 2).ToList();

            prod.ForEach((p) => Console.WriteLine(p.ToString()));

            Console.WriteLine($"Sum : {prod.Aggregate((a, b) => a + b)}");

            Console.ReadLine();

        }

​

        public static BigInteger[] Product(int n, int c)

        {

            var stopwatch = Stopwatch.StartNew();

            stopwatch.Start();

​

            BigInteger[] myProduct = new BigInteger[n];

            BigInteger[] myRange = new BigInteger[n];

            for (long i = 0; i < n ; i++)

            {

                myRange[i] = i;

            }

​

            for (long i = 1; i < myRange.Length ; i++)

            {

                if (i <= c)

                {

                    myProduct[i] = i;

                }

                else

                {

                    myProduct[i] = i;

                    var range = myRange.SubArray(((i+1) - c), c);

                    var p = range.Aggregate((a, b) => a * b);

                    myProduct[i] = p;

                }

            }

            stopwatch.Stop();

            Console.WriteLine("Time: " +  stopwatch.ElapsedMilliseconds);

            return myProduct;

        }

​

    }

​

    public static class IntExtention

    {

        public static BigInteger[] SubArray(this BigInteger[] data, long index, long length)

        {

            BigInteger[] result = new BigInteger[length];

            Array.Copy(data, index, result, 0, length);

            return result;

        }

    }

}

​