C#求一组数的众数

        private int GetModeNum(List<int> listValue)
        {
            List<int> listName = new List<int>(); //众数
            List<int> listNum = new List<int>();  //众数的数量
            int index = 0;
            foreach (var i in listValue)
            {
                int count = 0;
                if (!listName.Contains(i))
                {
                    foreach (var j in listValue)
                    {
                        if (i == j)
                        {
                            count++;
                        }
                    }
                    listName.Add(i);
                    listNum.Add(count);
                    index++;
                }
            }
            int max = 0, maxCount = 0, maxIndex = 0;
            for (int i = 0; i < index; i++)
            {
                max = max > listNum[i] ? max : listNum[i];
            }
            for (int i = 0; i < index; i++)
            {
                if (max == listNum[i])
                {
                    maxIndex = i;
                    maxCount++;
                }
            }
            if (maxCount > 0 && maxCount <= 1)
            {
                return listName[maxIndex];
            }
            else
            {
                return -1;
            }
        }

//调用
int a = this.GetModeNum(new List<int>() { 1, 2, 28, 36, 2, 1, 5, 1, 18, 28, 6, 15, 2, 2, 5, 5, 5,5 });
if (a != -1)
{
      Console.WriteLine("最多的数为：" + a);
}
else
{
      Console.WriteLine("最多的数有重复！");
}
Console.ReadLine();