找出数组中第二大数

如题，其实这个题目记得大学里教过的，即兴写了一个，记录代码如下：

    class Program
    {
        static void Main(string[] args)
        {
            int[] ar = { 1, 2, 6, 3, 4, 5 };
            try
            {
                Console.WriteLine(get2rdMax(ar).ToString());
            }
            catch(Exception exc)
            {
                Console.WriteLine(exc.Message);
            }
        }

        private static int get2rdMax(int[] ar)
        {
            int max=ar[1], s_max=ar[1];
            for (int i = 0; i < ar.Length; i++)
            {
                if (ar[i] > s_max)
                {
                    s_max = ar[i];
                    if (s_max > max)
                    {
                        max += s_max;
                        s_max = max - s_max;
                        max -= s_max;
                    }
                }
            }

            if (max == s_max)
                throw new Exception("no second max!");
            else
                return s_max;
        }
        

    } 

问上面这个问题的同学说{ 100, 3, 2, 6, 100, 9, 3, 4, 7 };就有漏洞了，我仔细查了下教科书中说的是不同的数。那么非得有重复的咋办呢？

以下是我的解决方案，并祝这位同学面试顺利！ 

    class Program
    {
        static void Main(string[] args)
        {
            int[] ar = { 1, 2, 6, 3, 4, 5 };
            int[] ar2 = { 100,100, 3, 2, 6, 100, 9, 3, 4, 7 };
            try
            {
                Console.WriteLine(get2rdMax(ar).ToString());
                Console.WriteLine(get2rdMax(ar2).ToString());
            }
            catch(Exception exc)
            {
                Console.WriteLine(exc.Message);
            }
        }

        private static int get2rdMax(int[] ar)
        {
            if (ar.Length < 2)
                throw new Exception("no second max!");

            int max=ar[0], s_max=ar[0];

            for (int i = 1; i < ar.Length; i++)
            {
                int index = ar[i];

                if (index == max)
                    continue;//重复值问题

                if (s_max == ar[0] && max == ar[0])
                {
                    s_max = index;
                }
                
                if (index > s_max)
                {
                    s_max = index;
                }

                if (s_max > max)
                {
                    max += s_max;
                    s_max = max - s_max;
                    max -= s_max;
                }
                
            }

            if (max == s_max)
                throw new Exception("no second max!");
            else
                return s_max;
        }
        

    }