C#大数阶乘算法

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using System;using System.Collections.Generic;using System.Linq;using System.Text;using System.Threading.Tasks;namespace 大数阶乘{    class Program    {        static void Main(string[] args)        {            Factorial fac = new Factorial(200000);            fac.Calculate();            Console.Write(fac.ToString());            Console.ReadKey();        }    }    public class Factorial    {        private int baseNumber = 100000;        public int BaseNumber        {            get            {                return baseNumber;            }        }        private int number;        private List<int> result = new List<int>();        public Factorial(int n)        {            number = n;            result = new List<int>();        }        public List<int> Calculate()        {            int digit = (int)System.Math.Log10(baseNumber);            int len = (int)(number * System.Math.Log10((number + 1) / 2) / digit);            len += 2;            int[] a = new int[len];            int i, j;            long c;            int m = 0;            a[0] = 1;            for (i = 2; i <= number; i++)            {                c = 0;                for (j = 0; j <= m; j++)                {                    long t = a[j] * i + c;                    c = t / baseNumber;                    a[j] = (int)(t % baseNumber);                }                while (c>0)                {                    m++;                    a[m] = (int)(c % baseNumber);                    c = c / baseNumber;                }            }            for (i = 0; i <= m; i++)            {                result.Add(a[i]);            }            return result;        }        public override string ToString()        {            if(result .Count ==0)            {                Calculate();            }            StringBuilder sb = new StringBuilder();            int digit = (int)System.Math.Log10(baseNumber);            sb.Append(result[result.Count - 1]);            for (int i = 0; i < result.Count; i++)            {                sb.Append(result[i].ToString().PadLeft(digit, '0'));            }            return sb.ToString();        }    }}

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