据说2017年10月2日反过来还是这样诶！——暴力求解法

namespace DateSwap
{
    class MainClass
    {
        public static void Main()
        {
            DateTime date = new DateTime(1, 1, 1);
            int count = 0;
            Dictionary<string, int> dic = new Dictionary<string, int>();
            for (;;)
            {
                if (date.Year == 9999 && date.Month == 12 && date.Day == 31) break;
                int ysize = 0, msize = 0, dsize = 0;
                string defaultDateString = DateTimeToString(date);
                //将各部分分开
                string[] ns = defaultDateString.Split(‘a‘);
                //得到各个部分的长度
                ysize = ns[0].Length;
                msize = ns[1].Length;
                dsize = ns[2].Length;

                //去掉本来的a,然后翻转
                string removed = defaultDateString.Replace("a", "");
                string changed = ReverseToArray(removed);

                DateTime ReverseDate = ReverseDateTime(changed, ysize, msize, dsize);
                if (date == ReverseDate) 
                {
                    Write(date.ToString("yyyy-MM-dd") + "\t" + ReverseDate.ToString("yyyy-MM-dd") + "\t");
                    WriteLine(date == ReverseDate);
                    count++;
                    string s = date.ToString("yyyy");
                }
                date = date.AddDays(1);
            }
            WriteLine(count);
            
        }

        private static string DateTimeToString(DateTime date)
        {
            return date.Year.ToString() +"a"+ date.Month.ToString() +"a"+ date.Day.ToString();
        }

        public static string ReverseToArray(string date)
        {
            char[] c = date.ToCharArray();
            Array.Reverse(c);
            return new string(c);
        }

        public static DateTime ReverseDateTime(string dateString, int ysize, int msize, int dsize)
        {
            List<char> list = new List<char>();
            for (int i = 0; i < ysize; i++)
                list.Add(dateString[i]);
            string year = new string(list.ToArray());
            list.Clear();

            for (int i = ysize; i < msize + ysize; i++)
                list.Add(dateString[i]);
            string month = new string(list.ToArray());
            list.Clear();

            for (int i = ysize + msize; i < msize + ysize + dsize; i++)
                list.Add(dateString[i]);
            string day = new string(list.ToArray());
            list.Clear();

            DateTime newdate;
            try
            {
                newdate = new DateTime(int.Parse(year), int.Parse(month), int.Parse(day));
            }
            catch(Exception)
            {
                newdate = new DateTime(9999, 12, 31, 1, 12, 3);
            }
            return newdate;
        }
    }
}