黑马程序员----计算1到n的数字中一共有多少1?最效率的方法

 

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace doomsday

{　　

　　  static long CountOne(long n)              

 　　 {
            long count = 0;
            long i = 1;
            long current = 0, after = 0, before = 0;
            while ((n / i) != 0)
            {
                current = (n / i) % 10;
                before = n / (i * 10);
                after = n - (n / i) * i;

                if (current > 1)
                    count = count + (before + 1) * i;
                else if (current == 0)
                    count = count + before * i;
                else if (current == 1)
                    count = count + before * i + after+ 1;

                i = i * 10;
            }
            return count;
        }

　　static void Main(string[] args)

　　{

            Console.WriteLine(CountOne(9999999999999));
            Console.ReadKey();

　　}

}

有很多方法解决这个问题，我觉得这个效率不错。