linq 两个list交集差集处理

 public object QuitChat(string groupId, string receiveMark)
        {
            try
            {
                //用户Mark转换
                List<string> receiveMarks = receiveMark.Split(',').ToList();
                if (receiveMarks.Count > 0)
                {
                    //组和用户Mark判断
                    List<GroupMemberManageEntity> userMark = _groupMemberManageAccess.GetModelListByGroupId(groupId);

                    if (userMark != null && userMark.Count > 0)
                    {
                        //组成员信息
                        var userMarks = userMark.Select(t => t.UserMark).ToList();
                        //交集
                        var intersect = receiveMarks.Intersect(userMarks).ToList();
                        if (intersect.Count == 0)
                        {
                            return new
                            {
                                code = (int)ResultCodeEnum.ParameterError,
                                msg = "receiveMark=" + string.Join(",", receiveMarks) + "参数不对!"
                            };
                        }
                        //差集
                        var except = receiveMarks.Except(intersect).ToList();

                        if (except.Count > 0)
                        {
                            return new
                            {
                                code = (int)ResultCodeEnum.ParameterError,
                                msg = "receiveMark=" + string.Join(",", except) + "参数不对!"
                            };
                        }
                        else
                        {
                            //被移除的组信息更新为不可用
                            foreach (var item in receiveMarks)
                            {
                                var groupMemberManage = userMark.FirstOrDefault(t => t.UserMark == item);
                                if (groupMemberManage != null)
                                {
                                    _groupMemberManageAccess.Update(groupMemberManage.Id,
                                        0); //review 七月：将此方法修改为只根据ID更新状态。
                                }
                            }

                            RemoveDialogGroupSearchModel removeDialogGroupSearchModel = new RemoveDialogGroupSearchModel
                            {
                                GroupId = groupId,
                                UserMark = receiveMark
                            };
                            //调用聊天服务移除接口
                            return RemoveDialogGroup(removeDialogGroupSearchModel);
                        }
                    }
                    else
                    {
                        return new
                        {
                            code = (int)ResultCodeEnum.ParameterError,
                            msg = "receiveMark=" + string.Join(",", receiveMarks) + "参数不对!"
                        };
                    }
                }
            }
            catch (Exception ex)
            {
                LogHelper.WriteLogForDll("结束会话接口，可指定人员退出", ex, $"groupId:{groupId}/receiveMark:{receiveMark}");
                return new
                {
                    code = (int)ResultCodeEnum.SystemException,
                    msg = "系统异常!"
                };
            }

            return new
            {
                code = (int)ResultCodeEnum.RequestSucess,
                msg = ""
            };
        }