/// <summary>
/// 结构：用于统计每个数出现的次数
/// </summary>
struct Stats
{
  //数字，出现的次数
  public double Number;
  public int Count;
  //构造函数
  public Stats(double n, int c) 
  { 
    Number = n;
    Count = c;
  }
}
/// <summary>
/// 计算数组的众数
/// </summary>
/// <param name="array">数组</param>
/// <param name="threshold">数量阈值，众数数量若多于次数则认为没有众数</param>
/// <returns></returns>
private static double[] ModeOf(double[] array, int threshold = 5)
{
  //数组排序-统计各元素数量-按各元素数量排序-再统计最多的元素
  //1.输入合法性检验
  if (array == null || array.Length == 0 || threshold < 1)
  {
    return new double[] { };
  }
  //2.制作数组副本，后面的操作将不修改数组本身
  double[] tempArray = new double[array.Length];
  array.CopyTo(tempArray,0);
  //3.数组排序
  double temp;
  for (int i = 0; i < tempArray.Length; i++)
  {
    for (int j = i; j < tempArray.Length; j++)
    {
      if (tempArray[i] < tempArray[j])
      {
        temp = tempArray[i];
        tempArray[i] = tempArray[j];
        tempArray[j] = temp;
      }
    }
  }
  //4.统计不同的元素数
  int counter = 1;
  for (int i = 1; i < tempArray.Length; i++)
  {
    if (tempArray[i] != tempArray[i - 1])
    {
      counter++;
    }
  }
  //5.统计各个元素数量
  int flag = 0;
  Stats[] statsArray = new Stats[counter];
  statsArray[flag].Number = tempArray[0];
  statsArray[flag].Count = 1;
  for (int i = 1; i < tempArray.Length; i++)
  {
    if (tempArray[i] == statsArray[flag].Number)
    {
      statsArray[flag].Count++;
    }
    else
    {
      flag++;
      statsArray[flag].Number = tempArray[i];
      statsArray[flag].Count = 1;
    }
  }
  //6.按元素在原数组内数量（Count属性）降序排列
  // 数量相等的元素则按大小升序排列
  for (int i = 0; i < statsArray.Length; i++)
  {
    for (int j = i; j < statsArray.Length; j++)
    {
      if (statsArray[i].Count < statsArray[j].Count ||
        (statsArray[i].Count == statsArray[j].Count &&
          statsArray[i].Number > statsArray[j].Number))
      {
        temp = statsArray[i].Number;
        statsArray[i].Number = statsArray[j].Number;
        statsArray[j].Number = temp;
        temp = statsArray[i].Count;
        statsArray[i].Count = statsArray[j].Count;
        statsArray[j].Count = (int)temp;
      }
    }
  }
  //7.统计众数数量
  int count = 1;
  if (statsArray.Length > threshold &&
    statsArray[threshold].Count == statsArray[0].Count)
  {
    //众数多余阈值数量，则认为没有众数
    return new double[] { };
  }
  else
  {
    for (int i = 1; i < statsArray.Length && i < threshold; i++)
    {
      if (statsArray[i].Count == statsArray[i - 1].Count)
      {
        count++;
      }
      else break;
    }
  }
  //8.生成返回众数数组
  double[] result = new double[count];
  for (int i = 0; i < count; i++)
  {
    result[i] = statsArray[i].Number;
  }
  return result;
}

static void Main(string[] args)
{
  //示例数组1
  double[] arr1 = new double[] 
  {
    3, 2, 7, 4, 8, 8, 5,
    5, 6, 5, 4, 3, 4, 9,
    1, 1, 1, 2, 2, 0, 6
  };
  double[] d1 = ModeOf(arr1);
  if (d1.Length != 0)
  {
    Console.Write("数组 1 有 " + d1.Length + " 个众数：");
    for (int i = 0; i < d1.Length; i++)
    {
      Console.Write(d1[i] + " ");
    }
    Console.WriteLine();
  }
  else
  {
    Console.WriteLine("数组 1 没有众数");
  }
  //示例数组2
  double[] arr2 = new double[] 
  {
    1, 2, 3, 4, 5, 6
  };
  double[] d2 = ModeOf(arr2);
  if (d2.Length != 0)
  {
    Console.Write("数组 2 有 " + d2.Length + " 个众数：");
    for (int i = 0; i < d2.Length; i++)
    {
      Console.Write(d2[i] + " ");
    }
    Console.WriteLine();
  }
  else
  {
    Console.WriteLine("数组 2 没有众数");
  }
  Console.ReadLine();
}