【ProjectEuler】ProjectEuler_020

using System;using System.Collections.Generic;using System.Text;namespace projecteuler020{    class Program    {        static void Main(string[] args)        {            F1();        }        private static void F1()        {            Console.WriteLine(new System.Diagnostics.StackTrace().GetFrame(0).GetMethod());            DateTime timeStart = DateTime.Now;            string result = "1";            int maxValue = 100;            int sum = 0;            for (int i = 1; i <= maxValue; i++)            {                result = longMulti(result, i);            }            for (int i = result.Length - 1; i >= 0; i--)            {                sum += result[i] - '0';            }            Console.WriteLine("100! = " + result);            Console.WriteLine("The sum of these digits is " + sum);            Console.WriteLine("Total Milliseconds is " + DateTime.Now.Subtract(timeStart).TotalMilliseconds + "\n\n");        }        private static string longMulti(string s1, int n)        {            string result = "0";            for (int i = 0; i < n; i++)            {                result = longAdd(result, s1, 0);            }            return result;        }        /// <summary>        /// 超大数字表达式加法        /// </summary>        /// <param name="s1">数1</param>        /// <param name="s2">数2</param>        /// <param name="c">后面的数的进位，范围0~2</param>        /// <returns></returns>        private static string longAdd(string s1, string s2, int c)        {            //s1,s2的末位Index            int l1 = s1.Length - 1;            int l2 = s2.Length - 1;            int x;            //如果2个数都不为空            if (l1 >= 0 && l2 >= 0)            {                x = s1[l1] - '0' + s2[l2] - '0' + c;                return longAdd(s1.Substring(0, l1), s2.Substring(0, l2), x / 10) + (x % 10).ToString();            }            //下面的情况，s1和s2中至少有一个为空，我们要做的是找到那个不为空的进行下一步操作            //把不为空的值放到s1里            if (l2 >= 0)            {                s1 = s2;                l1 = l2;            }            else if (l1 == -1)   //表示全为空，判断最后的进位，如果没进位，返回空白，结束递归            {                if (c != 0)                {                    return c.ToString();                }                return "";            }            x = s1[l1] - '0' + c;            //如果s1只有1位            if (l1 == 0)            {                return x.ToString();            }            //如果s1有不止一位            return longAdd(s1.Substring(0, l1), "", x / 10) + (x % 10).ToString();        }    }}/*Void F1()100! = 93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000The sum of these digits is 648Total Milliseconds is 436.5554*/