去除A和B数组中的交集

那位同学碰到新的算法题了。

去除A和B数组中的交集 ，即去除A和B数组中重复次数少的部分如A:111B:11,即去除B中的11

下面是我的解决方案，另希望他最后面试能过： 

    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;
        }
        

    }