public static List<int> reverseArray(List<int> a)
    {
        int[] arr = a.ToArray();
        int j = arr.Length-1;
        for(int i = 0; i<arr.Length;i++)
        {
            int change = arr[i];
            
                if (j > i)
                {
                    arr[i] = arr[j];
                    arr[j] = change;
                    j--;
                } 
            
        }
        return arr.ToList();
  }