[C# Lambda] 比對2個List差異 (List內容是多欄位Class)

class GroupedItem
{
    public string A { get; set; }
    public string B { get; set; }
    public int TotalC { get; set; }
}

class Program
{
    static void Main()
    {
        List<GroupedItem> list1 = new List<GroupedItem>
        {
            new GroupedItem { A = "A1", B = "B1", TotalC = 10 },
            new GroupedItem { A = "A2", B = "B2", TotalC = 15 },
            new GroupedItem { A = "A3", B = "B3", TotalC = 20 }
        };

        List<GroupedItem> list2 = new List<GroupedItem>
        {
            new GroupedItem { A = "A1", B = "B1", TotalC = 10 },
            new GroupedItem { A = "A2", B = "B2", TotalC = 16 },
            new GroupedItem { A = "A4", B = "B4", TotalC = 25 }
        };

        var groupedAndSelected1 = list1.GroupBy(item => new { item.A, item.B })
                                       .Select(group => new GroupedItem
                                       {
                                           A = group.Key.A,
                                           B = group.Key.B,
                                           TotalC = group.Sum(item => item.TotalC)
                                       });

        var groupedAndSelected2 = list2.GroupBy(item => new { item.A, item.B })
                                       .Select(group => new GroupedItem
                                       {
                                           A = group.Key.A,
                                           B = group.Key.B,
                                           TotalC = group.Sum(item => item.TotalC)
                                       });

        var result = CompareGroupedItems(groupedAndSelected1.ToList(), groupedAndSelected2.ToList());

        Console.WriteLine("Added items:");
        foreach (var item in result.AddedItems)
        {
            Console.WriteLine($"A={item.A}, B={item.B}, TotalC={item.TotalC}");
        }

        Console.WriteLine("Removed items:");
        foreach (var item in result.RemovedItems)
        {
            Console.WriteLine($"A={item.A}, B={item.B}, TotalC={item.TotalC}");
        }
    }

    static (List<GroupedItem> AddedItems, List<GroupedItem> RemovedItems) CompareGroupedItems(List<GroupedItem> list1, List<GroupedItem> list2)
    {
        var addedItems = list1.Except(list2, new GroupedItemComparer()).ToList();
        var removedItems = list2.Except(list1, new GroupedItemComparer()).ToList();

        return (addedItems, removedItems);
    }
}

class GroupedItemComparer : IEqualityComparer<GroupedItem>
{
    public bool Equals(GroupedItem x, GroupedItem y)
    {
        if (x == null || y == null)
            return false;

        return x.A == y.A && x.B == y.B && x.TotalC == y.TotalC;
    }

    public int GetHashCode(GroupedItem obj)
    {
        return (obj.A + obj.B + obj.TotalC).GetHashCode();
    }
}