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  • Algorithm design: can you provide a solution to the multiple knapsack problem?

    - by MalcomTucker
    I am looking for a pseudo-code solution to what is effectively the Multiple Knapsack Problem (optimisation statement is halfway down the page). I think this problem is NP Complete so the solution doesn't need to be optimal, rather if it is fairly efficient and easily implemented that would be good. The problem is this: I have many work items, with each taking a different (but fixed and known) amount of time to complete. I need to divide these work items into groups so as to have the smallest number of groups (ideally), with each group of work items taking no longer than a given total threshold - say 1 hour. I am flexible about the threshold - it doesnt need to be rigidly applied, though should be close. My idea was to allocate work items into bins where each bin represents 90% of the threshold, 80%, 70% and so on. I could then match items that take 90% to those that take 10%, and so on. Any better ideas?

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  • What design pattern should be used to create an emulator?

    - by Facon
    I have programmed an emulator, but I have some doubts about how to organizate it properly, because, I see that it has some problems about classes connection (CPU <- Machine Board). For example: I/O ports, interruptions, communication between two or more CPU, etc. I need for the emulator to has the best performance and good understanding of the code. PD: Sorry for my bad English.

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  • Icons: How does a developer with no design skill make his/her application icons look pretty?

    - by Martin
    I probably spend far too much time trying to make my visual interfaces look good, and while I'm pretty adept at finding the right match between usability and style one area I am hopeless at is making nice looking icons. How do you people overcome this (I'm sure common) problem? I'm thinking of things like images on buttons and perhaps most important of all, the actual application icon. Do you rely on third party designers, in or out of house? Or do you know of some hidden website that offers lots of icons for us to use? I've tried Google but I seem to find either expensive packages that are very specific, millions of Star Trek icons or icons that look abysmal at 16x16 which is my preferred size on in-application buttons. Any help/advice appreciated.

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  • How to Map a table with another lookup table using JPA?

    - by Sameer Malhotra
    Hi, I have two tables: 1) Application(int appid, int statusid, String appname, String appcity with getter and Setter methods) 2) App_Status(int statusid,String statusDescription with setter and getter methods) I want to map Application table with App_Status so that I don't have to query separately App_Status table in order to get the statusDescription. One thing I have to careful is that no matter what (Insert,update or delete) to the Application table the App_Status table should be unaffected means its a read only table which is maintained by the DBA internally and used only for lookup table. I am using JPA annotations so please suggest how to handle this.

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  • Modeling many-to-one with constraints?

    - by Greg Beech
    I'm attempting to create a database model for movie classifications, where each movie could have a single classification from each of one of multiple rating systems (e.g. BBFC, MPAA). This is the current design, with all implied PKs and FKs: TABLE Movie ( MovieId INT ) TABLE ClassificationSystem ( ClassificationSystemId TINYINT ) TABLE Classification ( ClassificationId INT, ClassificationSystemId TINYINT ) TABLE MovieClassification ( MovieId INT, ClassificationId INT, Advice NVARCHAR(250) -- description of why the classification was given ) The problem is with the MovieClassification table whose constraints would allow multiple classifications from the same system, whereas it should ideally only permit either zero or one classifications from a given system. Is there any reasonable way to restructure this so that a movie having exactly zero or one classifications from any given system is enforced by database constraints, given the following requirements? Do not duplicate information that could be looked up (i.e. duplicating ClassificationSystemId in the MovieClassification table is not a good solution because this could get out of sync with the value in the Classification table) Remain extensible to multiple classification systems (i.e. a new classification system does not require any changes to the table structure)? Note also the Advice column - each mapping of a movie to a classification needs to have a textual description of why that classification was given to that movie. Any design would need to support this.

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  • join 03 table in the database codeIgniter

    - by python
    with my table. person_id serial NOT NULL, firstname character varying(30) NOT NULL, lastname character varying(30), email character varying(50), username character varying(20) NOT NULL, "password" character varying(100) NOT NULL, gender character varying(10), dob date, accesslevel smallint NOT NULL, company_id integer NOT NULL,//Reference to table company position_id integer NOT NULL,//Reference to table position company_id serial NOT NULL, company_name character varying(80) NOT NULL, description character varying(255), address character varying(100) NOT NULL, In my controller ........................ // load data $persons = $this->person_model->get_paged_list(10,0); // generate table data $this->load->library('table'); $this->table->set_empty("&nbsp;"); $this->table->set_heading('No', 'FirstName', 'LastName','E-mail','Company''Gender', 'Date of Birth', 'Actions'); foreach ($persons as $person){ $this->table->add_row(++$i, $person->firstname, $person->lastname, $person->email, $person->company_name, //HOW CAN I GOT THE POSITION TITLE ?, strtoupper($person->gender)=='M'? 'Male':'Female', date('d-m-Y',strtotime($person->dob)), } My model <?php class Person_Model extends Model { private $person= 'person'; function Person(){ parent::Model(); } function list_all(){ $this->db->order_by('person_id','asc'); return $this->db->get($person); } function count_all(){ return $this->db->count_all($this->person); } function get_paged_list($limit = 0, $offset = 0) { $this->db->limit($limit, $offset); $this->db->select("person.*, company.company_name as company"); $this->db->from('person'); $this->db->join('company','person.company_id = company.company_id','left'); //MY QUESTION:? CAN I JOIN MORE WITH TABLE POSITION? $query = $this->db->get(); return $query->result(); } function get_by_id($id){ $this->db->where('person_id', $id); return $this->db->get($this->person); } function save($person){ $this->db->insert($this->person, $person); return $this->db->insert_id(); } function update($id, $person){ $this->db->where('person_id', $id); $this->db->update($this->person, $person); } function delete($id){ $this->db->where('person_id', $id); $this->db->delete($this->person); } } ?>

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  • database design: table with large amount of columns (50+) or many sub tables with small amount of co

    - by Guillaume
    In our oroject we already have a lots of tables (100+). Some of them contains a lot of columns (50-100) and we are facing the need of adding more columns from time to time. What do you think is best - from maintenance and performance point of view - to split these huge tables in smaller entities or to keep the tables the way they are ? We are using an ORM tools, so we don't need to write custom request.

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  • Truncating a table referenced by a foreign key

    - by born to hula
    Hey, We have two tables in a SQL Server 2005 database, A and B.There is a service which truncates table A every day. Recently, a foreign key constraint was added to table B, referencing table A. As a result, it isn't possible truncating table A anymore, even if table B is empty. Is there any workaround to get the same result as truncating table A? I've already tried the approach below but the identity wasn't reset. DBCC CHECKIDENT (TABLENAME, RESEED, 0) PS. before anyone points this as a duplicate, the different thing here is that I'm not allowed to drop constraints, nor creating any.

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  • How to design the application to conform to the n-tier architecture? (Winform sample in .net with li

    - by AlexRednic
    Rather a simple question. But the implications are vast. Over the last few weeks I've been reading a lot of material about n-tier architecture and it's implementation in the .NET world. The problem is I couldn't find a relevant sample for Winforms with Linq (linq is the way to go for BLL right?). How did you guys manage to grasp the n-tier concept? Books, articles, relevant samples etc.

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  • read contents of a sql table into a data grid view

    - by syedsaleemss
    Im using c# .net windows application form. i have created a database named "resources" in SQL server 2005. In that i have a table named "resourcetable" which has two columns. now i need to read the data in the table into a datagridview. I can do this by using the connection string and querry by giving the table name. But my problem is i have a button and if i click on that button, an open dialog box should open and i should be able to select a database amomng many databases and in that selected database i have to select one table amomg many tables. i.e select a table ofa particular database. and the contents of that table are to be displayed in a datagridview.

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  • c++ design question: Can i query the base classes to find the number of derived classes satisfying a

    - by vivekeviv
    I have a piece of code like this class Base { public: Base(bool _active) { active = _active; } void Configure(); void Set Active(bool _active); private: bool active; }; class Derived1 : public Base { public: Derived1(bool active):Base(active){} }; similarly Derived 2 and Derived 3 Now if i call derived1Object.Configure, i need to check how many of the derived1Obj, derived2Obj,derived3Obj is active. Should i add this in the "Base" class like a function say, GetNumberOfActive()? And If the implementation is like this: class Imp { public: void Configure() { //Code instantiating a particular Derived1/2/3 Object int GetNumberOfActiveDerivedObj(); baseRef.Configure(int numberOfActiveDerivedClasses); } prive: Derived1 dObj1(true); Derived2 dObj2(false); Derived3 dObj3(true); }; should i calculate the numberOfActive Derived Objects in Imp Class? THanks

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  • SQL Server Express: Failed to add primary key after creating a database table

    - by Syd
    Scenario: I have created a database table. And when I tried to add a primary key (using the SQL Server Management Studiio) to the table, it failed with an error message "Saving changes is not permitted. The changes you have made requrie the following tables to be dropped and re-created. You have either made changes to a table that can't be recreated or enabled the option Prevent savign changes that require the table to be re-created." The environment is Windows 7. I have earlier installed it on a Windows XP SP2 and it worked. And yes, my table is empty (freshly created). My current workaround is to run the "Drop and Create" script. The other alternative is to create the primary key before I save the table. Is this a bug or a limitation with the Express version?

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  • How to handle product ratings in a database

    - by Mel
    Hello, I would like to know what is the best approach to storing product ratings in a database. I have in mind the following two (simplified, and assuming a MySQL db) scenarios: Scenario 1: Create two columns in the product table to store number of votes and the sum of all votes. Use columns to get an average on the product display page: products(productedID, productName, voteCount, voteSum) Pros: I will only need to access one table, and thus execute one query to display product data and ratings. Cons: Write operations will be executed in a table whose original purpose is only to furnish product data. Scenario 2: Create an additional table to store ratings. products(productID, productName) ratings(productID, voteCount, voteSum) Pros: Isolate ratings into a separate table, leaving the products table to furnish data on available products. Cons: I will have to execute two separate queries on product page requests (one for data and another for ratings). In terms of performance, which of the following two approaches is best: Allow users to execute an occasional write query to a table that will handle hundreds of read requests? Execute two queries at every product page, but isolate the write query into a separate table. I'm a novice to database development, and often find myself struggling with simple questions such as these. Many thanks,

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  • how to design a db like Facebook where users can update their status and of the fb page as admin

    - by Harsha M V
    i am designing a database where users can update status messages of theirs and they can create pages groups like facebook fan page and post status like the admin of the page and not as a user. user(id, name..) group(id, name...) group_admin(group_id, user_id) this is my set up. Is this the way to do it. How to post under the group as an admin. will i need to make a check to every user if he is the admin or not ?

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  • MySQL Join a Table if Exists Question

    - by swhitlow
    I have a DB which has a table called "config". This table could possibly have a "config_cstm" table that is related by the id to the config table. I was wondering - is there a way to dynamically check for the existence of this table in one simple select statement? In other words, something like: "select * from config (IF EXISTS config_cstm THEN LEFT OUTER JOIN config_cstm ON config.id = config_cstm.id_c" I know how I would go about checking for the existence of an existing table in PHP. I was wanting to do this all in one MySQL statement though. Any suggestions? Thanks!

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  • Multiplayer card game using PHP/Ajax and mysql

    - by Alireza Seifi
    I am designing a map game, using PHP and MYSQL. I don't know how to make the players who sign-in to the website to see other players who are also connected to the site and be able to chat with one another. I want to design the game in such a way that 2 players can play with each other and be able to send messages during the game while others groups are playing at the same time. I have designed the map game successfully, but the problem is making the player 1 who log-in to site to see the player 2 who will also log-in and both can get connected to play each other. http://i.stack.imgur.com/YyCPG.png I will appreciate your responses.

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  • SQL SERVER – When are Statistics Updated – What triggers Statistics to Update

    - by pinaldave
    If you are an SQL Server Consultant/Trainer involved with Performance Tuning and Query Optimization, I am sure you have faced the following questions many times. When is statistics updated? What is the interval of Statistics update? What is the algorithm behind update statistics? These are the puzzling questions and more. I searched the Internet as well many official MS documents in order to find answers. All of them have provided almost similar algorithm. However, at many places, I have seen a bit of variation in algorithm as well. I have finally compiled the list of various algorithms and decided to share what was the most common “factor” in all of them. I would like to ask for your suggestions as whether following the details, when Statistics is updated, are accurate or not. I will update this blog post with accurate information after receiving your ideas. The answer I have found here is when statistics are expired and not when they are automatically updated. I need your help here to answer when they are updated. Permanent table If the table has no rows, statistics is updated when there is a single change in table. If the number of rows in a table is less than 500, statistics is updated for every 500 changes in table. If the number of rows in table is more than 500, statistics is updated for every 500+20% of rows changes in table. Temporary table If the table has no rows, statistics is updated when there is a single change in table. If the number of rows in table is less than 6, statistics is updated for every 6 changes in table. If the number of rows in table is less than 500, statistics is updated for every 500 changes in table. If the number of rows in table is more than 500, statistics is updated for every 500+20% of rows changes in table. Table variable There is no statistics for Table Variables. If you want to read further about statistics, I suggest that you read the white paper Statistics Used by the Query Optimizer in Microsoft SQL Server 2008. Let me know your opinions about statistics, as well as if there is any update in the above algorithm. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Pinal Dave, Readers Question, SQL, SQL Authority, SQL Optimization, SQL Performance, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology Tagged: SQL Statistics

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