C#斐波那契数列求法（比较阶乘和循环所用时间）

using system;

namespace consoleapp3
{
    class program
    {
        static void main(string[] args)
        {
            console.write("你要输入多少项？");
            int a = convert.toint32(console.readline());
            console.writeline();
            datetime dt1 = system.datetime.now;
            for (int i = 1; i <= a; i++)
            {
                console.write("\t{0}", j(i));
                if (i % 5 == 0)
                {
                    console.writeline();
                }
            }
            datetime dt2 = system.datetime.now;
            timespan ts = dt2.subtract(dt1);
            console.writeline("3变量循环方法用时{0}", ts.totalmilliseconds);//3变量循环方法所用时间

            datetime dt11 = system.datetime.now;
            for (int i = 1; i <= a; i++)
            {
                console.write("\t{0}", j1(i));
                if (i % 5 == 0)
                {
                    console.writeline();
                }
            }
            datetime dt22 = system.datetime.now;
            timespan ts1 = dt22.subtract(dt11);
            console.writeline("2变量循环方法用时{0}", ts1.totalmilliseconds);//2变量循环方法所用时间

            datetime dt111 = system.datetime.now;
            for (int i = 1; i <= a; i++)
            {
                console.write("\t{0}", j2(i));
                if (i % 5 == 0)
                {
                    console.writeline();
                }
            }
            datetime dt222 = system.datetime.now;
            timespan ts11 = dt222.subtract(dt111);
            console.writeline("递归方法用时{0}", ts11.totalmilliseconds);//递归方法所用时间
        }
        /// <summary>
        /// 3个变量循环求斐波那契数列
        /// </summary>
        /// <param name="b"></param>
        /// <returns></returns>
        static int j(int b)
        {
            int x = 1;
            int y = 1;
            if (b == 1 || b == 2)
            {
                return 1;
            }
            else
            {
                for (int i = 3; i <= b; i++)
                {
                    int z = x + y;
                    y = x;
                    x = z;
                }
                return x;
            }
        }
        /// <summary>
        /// 2个变量循环求斐波那契数列
        /// </summary>
        /// <param name="b"></param>
        /// <returns></returns>
        static int j1(int b)
        {
            int x = 1;
            int y = 1;
            if (b == 1 || b == 2)
            {
                return 1;
            }
            else
            {
                for (int i = 3; i <= b; i++)
                {
                    y = x + y;
                    x = y-x;
                }
                return y;
            }
        }

        /// <summary>
        /// 阶乘求斐波那契数列
        /// </summary>
        /// <param name="b"></param>
        /// <returns></returns>
        static int j2(int b)
        {
            if (b == 1 || b == 2)
            {
                return 1;
            }
            else
            {
                return j2(b - 1) + j2(b - 2);
            }
        }
    }
}