namespace 过河卒
{
    class Program
    {
        const int RowsOFBoard = 20 , ColumnsOFboard = 20; 

        int X_Horse, Y_Horse, X_B, Y_B;

        static int result = 0;

        int[,] board = new int[RowsOFBoard, ColumnsOFboard];
        
        void InitBoard()                //根据马的位置初始化棋盘
        {
            board[X_Horse, Y_Horse] = 1;
            board[X_B, Y_B] = 5;
            for(int factor=-1;factor<3;factor+=2)
            {

                if (LegalJudge(X_Horse + factor * 1, Y_Horse + factor * 2)) 
                    board[X_Horse + factor * 1, Y_Horse + factor * 2] = 1;


                if (LegalJudge(X_Horse + factor * 2, Y_Horse + factor * 1))
                    board[X_Horse + factor * 2, Y_Horse + factor * 1] = 1;


                if (LegalJudge(X_Horse + factor * 1, Y_Horse + factor * -2))
                    board[X_Horse + factor * 1, Y_Horse + factor * -2] = 1;


                if (LegalJudge(X_Horse + factor * 2, Y_Horse + factor * -1))
                    board[X_Horse + factor * 2, Y_Horse + factor * -1] = 1;

            }

        }
         bool LegalJudge(int x,int y)
        {
            return x >= 0 && y >= 0 &&x<RowsOFBoard && y<ColumnsOFboard;
        }
        bool QuickJudge_Row(int x, int y)
        {
            return x <= X_B && board[x, y] != 1;
        }
        bool QuickJudge_Column(int x, int y)
        {
            return y <= Y_B && board[x, y] != 1;
        }


        void DFS(int x,int y)
        {
            if (x + 1 == X_B && y == Y_B)
            {
                result++;
                return;
            }    
                
            else
            {
                if(QuickJudge_Row(x+1,y))
                    DFS(x + 1, y);
            }                        

            if (x == X_B && y == Y_B)
            {
                result++;
                return;
            }
            else
            {
                if (QuickJudge_Column(x , y+1))
                    DFS(x, y+1);
            }         
        }

        //输出棋盘,测试用
         void CW()
        {
            for (int i = 0; i < board.GetLength(0); i++)
            {
                for (int t = 0; t < board.GetLength(1); t++)
                    Console.Write(board[i, t]+" ");
                Console.WriteLine("");
            }
        }

        static void Main(string[] args)
        {
            Program program = new Program();
            //Console.WriteLine("请分别输入马和B的坐标");
            string[] text = Console.ReadLine().Split(' ');

            program.X_Horse = Int32.Parse(text[2]);
            program.Y_Horse = Int32.Parse(text[3]);
            program.X_B = Int32.Parse(text[0]);
            program.Y_B = Int32.Parse(text[1]);


            program.InitBoard();
           // program.CW();
            program.DFS(0, 0);
            Console.WriteLine(result);
        }
    }
}

测试时B的坐标一旦大起来（十几）确实会耗时过多

比如：

15 17 5 8
119833848
DateTime costed is: 8183.4199ms

hxd们，瓶颈在哪里？