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• Most Astonishing Violation of the Principle of Least Astonishment

  - by Adam Liss

  The Principle of Least Astonishment suggests that a system should operate as a user would expect it to, as much as possible. In other words, it should never "astonish" the user with unexpected behavior. In your experience as the "astonishee," what types of systems are the worst offenders, and if you were the project manager, how would you correct the problem? Bonus if your answer describes how you'd retrain the developers!

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• GRAPH PROBLEM: find an algorithm to determine the shortest path from one point to another in a recta

  - by newba

  I'm getting such an headache trying to elaborate an appropriate algorithm to go from a START position to a EXIT position in a maze. For what is worth, the maze is rectangular, maxsize 500x500 and, in theory, is resolvable by DFS with some branch and bound techniques ... 10 3 4 7 6 3 3 1 2 2 1 0 2 2 2 4 2 2 5 2 2 1 3 0 2 2 2 2 1 3 3 4 2 3 4 4 3 1 1 3 1 2 2 4 2 2 1 Output: 5 1 4 2 Explanation: Our agent looses energy every time he gives a step and he can only move UP, DOWN, LEFT and RIGHT. Also, if the agent arrives with a remaining energy of zero or less, he dies, so we print something like "Impossible". So, in the input 10 is the initial agent's energy, 3 4 is the START position (i.e. column 3, line 4) and we have a maze 7x6. Think this as a kind of labyrinth, in which I want to find the exit that gives the agent a better remaining energy (shortest path). In case there are paths which lead to the same remaining energy, we choose the one which has the small number of steps, of course. I need to know if a DFS to a maze 500x500 in the worst case is feasible with these limitations and how to do it, storing the remaining energy in each step and the number of steps taken so far. The output means the agent arrived with remaining energy= 5 to the exit pos 1 4 in 2 steps. If we look carefully, in this maze it's also possible to exit at pos 3 1 (column 3, row 1) with the same energy but with 3 steps, so we choose the better one. With these in mind, can someone help me some code or pseudo-code? I have troubles working this around with a 2D array and how to store the remaining energy, the path (or number of steps taken)....

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• Algorithm to represent Decision tables

  - by driveBy

  What would be the best algorithm to use if you wanted to store Decision tables in code, i've looked at the Adjacency matrix and Binary tree would anyone consider this to be the right direction? What other choices to I have?

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• Codechef practice question help needed - find trailing zeros in a factorial

  - by manugupt1

  I have been working on this for 24 hours now, trying to optimize it. The question is how to find the number of trailing zeroes in factorial of a number in range of 10000000 and 10 million test cases in about 8 secs. The code is as follows: #include<iostream> using namespace std; int count5(int a){ int b=0; for(int i=a;i>0;i=i/5){ if(i%15625==0){ b=b+6; i=i/15625; } if(i%3125==0){ b=b+5; i=i/3125; } if(i%625==0){ b=b+4; i=i/625; } if(i%125==0){ b=b+3; i=i/125; } if(i%25==0){ b=b+2; i=i/25; } if(i%5==0){ b++; } else break; } return b; } int main(){ int l; int n=0; cin>>l; //no of test cases taken as input int *T = new int[l]; for(int i=0;i<l;i++) cin>>T[i]; //nos taken as input for the same no of test cases for(int i=0;i<l;i++){ n=0; for(int j=5;j<=T[i];j=j+5){ n+=count5(j); //no of trailing zeroes calculted } cout<<n<<endl; //no for each trialing zero printed } delete []T; } Please help me by suggesting a new approach, or suggesting some modifications to this one.

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• How to maintain an ordered table with Core Data (or SQL) with insertions/deletions?

  - by Jean-Denis Muys

  This question is in the context of Core Data, but if I am not mistaken, it applies equally well to a more general SQL case. I want to maintain an ordered table using Core Data, with the possibility for the user to: reorder rows insert new lines anywhere delete any existing line What's the best data model to do that? I can see two ways: 1) Model it as an array: I add an int position property to my entity 2) Model it as a linked list: I add two one-to-one relations, next and previous from my entity to itself 1) makes it easy to sort, but painful to insert or delete as you then have to update the position of all objects that come after 2) makes it easy to insert or delete, but very difficult to sort. In fact, I don't think I know how to express a Sort Descriptor (SQL ORDER BY clause) for that case. Now I can imagine a variation on 1): 3) add an int ordering property to the entity, but instead of having it count one-by-one, have it count 100 by 100 (for example). Then inserting is as simple as finding any number between the ordering of the previous and next existing objects. The expensive renumbering only has to occur when the 100 holes have been filled. Making that property a float rather than an int makes it even better: it's almost always possible to find a new float midway between two floats. Am I on the right track with solution 3), or is there something smarter?

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• O(log n) algorithm for computing rank of union of two sorted lists?

  - by Eternal Learner

  Given two sorted lists, each containing n real numbers, is there a O(log?n) time algorithm to compute the element of rank i (where i coresponds to index in increasing order) in the union of the two lists, assuming the elements of the two lists are distinct? I can think of using a Merge procedure to merge the 2 lists and then find the A[i] element in constant time. But the Merge would take O(n) time. How do we solve it in O(log n) time?

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• Best option for using the GData APIs on Android?

  - by nyenyec

  What's the least painful and most size efficient way to use the Google Data APIs in an Android application? After a few quick searches t seems that there is an android-gdata project on Google Code that seems to be the work of a single author. I didn't find any documentation for it and don't even know if it's production ready yet. An older option, the com.google.wireless.gdata package seems to have been removed from the SDK. It's still available in the GIT repository. Before I invest too much time with either approach I'd like to know which is the best supported and least painful.

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• Synonym for "Many-to-Many" relationship (relational databases)

  - by Byron

  What's a synonym for a "many-to-many" relationship? I've finished writing an object-relational mapper but I'm still stumped as to what to name the function that adds that relation. addParent() and addChild() seemed quite logical for the many-to-one/one-to-many and addSuperclass() for one-to-one inheritance, but addManyToMany() would sound quite unintuitive to an object-oriented programmer. addSibling() or addCousin() doesn't really make sense either. Any suggestions? And before you dismiss this as a non-programming question, please remember that consistent naming schemes and encapsulation are pretty integral to programming :)

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• Using Facebook Connect auth.RevokeAuthorization in ASP.NET

  - by Focus

  I'm confused as to how revoking authorization works in the ASP.NET Toolkit. I've tried issuing the following: ConnectSession connect = new ConnectSession(FacebookHelper.ApiKey(), FacebookHelper.SecretKey()); Auth x = new Auth(fbSession); x.RevokeAuthorization(); But I get an object reference error during the RevokeAuthorization call. Here's the call definition. Any idea what I'm doing wrong?

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• How to Manage project in this scenario

  - by vijay.shad

  Hi All, I am working on a web application which has got good amount of static or pre-login pages. These pages can have some simple forms as well where we would like to capture the visitor's details. Post login, I have got my main application. I am confused about the development and deployment architecture of my application. Post login part of my application has a release cycle of 1-2 months while pre-login pages are to be updated on a weekly basis. It is difficult to make a release of pre-login pages as the overall war also contains post-login application & which sometimes is not release ready. Currently, I have got both these parts bundled in the single war project. Please help me by letting me know the best practices whereby I can achieve following: Manage the releases of these two parts independently. I am using Maven. So is there a way I can share the resources, such as CSS, images etc between these two parts. Header and footer of my application is going to be same on pre-login & post-login pages. I was thinking of deploying these apps as two war files in my tomcat container. But then how will I manage the common resources like Css, images etc. Rgds Vijay

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• Evenly select N elems from array

  - by ninuhadida

  Hi, I need to evenly select n elements from an array. I guess the best way to explain is by example. say I have: array [0,1,2,3,4] and I need to select 3 numbers.. 0,3,4. of course, if the array length <= n, I just need to return the whole array. I'm pretty sure there's a defined algorithm for this, been trying to search, and I took a look at Introduction to algorithms but couldn't find anything that met my needs (probably overlooked it) The problem I'm having is that I can't figure out a way to scale this up to any array [ p..q ], selecting N evenly elements. note: I can't just select the even elements from the example above.. A couple other examples; array[0,1,2,3,4,5,6], 3 elements ; I need to get 0,3,6 array[0,1,2,3,4,5], 3 elements ; I need to get 0, either 2 or 3, and 5

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• Why is it bad to use boolean flags in databases? And what should be used instead?

  - by David Chanin

  I've been reading through some of guides on database optimization and best practices and a lot of them suggest not using boolean flags at all in the DB schema (ex http://forge.mysql.com/wiki/Top10SQLPerformanceTips). However, they never provide any reason as to why this is bad. Is it a peformance issue? is it hard to index or query properly? Furthermore, if boolean flags are bad, what should you use to store boolean values in a database? Is it better to store boolean flags as an integer and use a bitmask? This seems like it would be less readable.

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• Any Win32 APIs to get the screenshots?

  - by Microkernel

  Hi all, I am writing an app, which needs to take the screen shots automatically (just like pressing PrintScreen button). So please suggest me how to get this done. A raw 24 bit BMP image would suffice. PLEASE NOTE: My app is in C, so any win32 APIs that can be called from my code is what I am looking for. (Sometimes back I had got an example code from codeproject which used to get the screen shots but the mouse pointer user to blink when the screen shot is taken. As multiple shots are taken this looks irritating to the user, so I don't want the mouse pointer to blink!) Regards, Chethan KR

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• How to make this OO?

  - by John

  Hello, Sorry for the poor title,I'm new to OOP so I don't know what is the term for what I need to do. I have, say, 10 different Objects that inherit one Object.They have different amount and type of class members,but all of them have one property in common - Visible. type TObj1=class(TObject) private a:integer; ...(More members) Visible:Boolean; end; TObj2=class(TObject) private b:String; ...(More members) Visible:Boolean; end; ...(Other 8 objects) For each of them I have a variable. var Obj1:TObj1; Obj2:TObj2; Obj3:TObj3; ....(Other 7 objects) Rule 1: Only one object can be initialized at a time(others have to be freed) to be visible. For this rule I have a global variable var CurrentVisibleObj:TObject; //Because they all inherit TObject Finally there is a procedure that changes visibility. procedure ChangeObjVisibility(newObj:TObject); begin CurrentVisibleObj.Free; //Free the old object CurrentVisibleObj:=newObj; //assign the new object CurrentVisibleObj:= ??? //Create new object CurrentVisibleObj.Visible:=true; //Set visibility to new object end; There is my problem,I don't know how to initialize it,because the derived class is unknown. How do I do this? I simplified the explanation,in the project there are TFrames each having different controls and I have to set visible/not visible the same way(By leaving only one frame initialized). Sorry again for the title,I'm very new to OOP.

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• Register all GUI components as Observers or pass current object to next object as a constructor argu

  - by Jack

  First, I'd like to say that I think this is a common issue and there may be a simple or common solution that I am unaware of. Many have probably encountered a similar problem. Thanks for reading. I am creating a GUI where each component needs to communicate (or at least be updated) by multiple other components. Currently, I'm using a Singleton class to accomplish this goal. Each GUI component gets the instance of the singleton and registers itself. When updates need to be made, the singleton can call public methods in the registered class. I think this is similar to an Observer pattern, but the singleton has more control. Currently, the program is set up something like this: class c1 { CommClass cc; c1() { cc = CommClass.getCommClass(); cc.registerC1( this ); C2 c2 = new c2(); } } class c2 { CommClass cc; c2() { cc = CommClass.getCommClass(); cc.registerC2( this ); C3 c3 = new c3(); } } class c3 { CommClass cc; c3() { cc = CommClass.getCommClass(); cc.registerC3( this ); C4 c4 = new c4(); } } etc. Unfortunately, the singleton class keeps growing larger as more communication is required between the components. I was wondering if it's a good idea to instead of using this singleton, pass the higher order GUI components as arguments in the constructors of each GUI component: class c1 { c1() { C2 c2 = new c2( this ); } } class c2 { C1 c1; c2( C1 c1 ) { this.c1 = c1 C3 c3 = new c3( c1, this ); } } class c3 { C1 c1; C2 c2; c3( C1 c1, C2 c2 ) { this.c1 = c1; this.c2 = c2; C4 c4 = new c4( c1, c2, this ); } } etc. The second version relies less on the CommClass, but it's still very messy as the private member variables increase in number and the constructors grow in length. Each class contains GUI components that need to communicate through CommClass, but I can't think of a good way to do it. If this seems strange or horribly inefficient, please describe some method of communication between classes that will continue to work as the project grows. Also, if this doesn't make any sense to anyone, I'll try to give actual code snippets in the future and think of a better way to ask the question. Thanks.

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• Algorithm for max integer in an array of integers

  - by gagneet

  Explain which algorithm you would use to implement a function that takes an array of integers and returns the maximum integer in the collection, assuming that the length of the array is less than 1000. Would you use Bubble Sort or Merge Sort and Why? Also, what happens to the above algorithm choice, if the array length is greater than 1000?

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• What open source database platform is most easily transferred from my personal machine into a window

  - by Tom

  I would like eventual interaction with MS Dynamics SL and/or MindTouch Core (running on WMware) for eventual intranet and/or internet display. I guess I am asking for front and back end recommendations for a database I am constructing, but since this is my first major project I would greatly appreciate any help and advice. I would also love an opportunity to learn a new language so the code base could be in any language. I do have a few more related questions for discussion; What is the viability of using Google hosting to provide the service to the public for free? Should I implement plone or another CMS if I have a large amount of output? Is there a structuring questionnaire or standards publication I could reference? Does UML diagramming provide additional options for portability? Thank you.

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• Circular Dependency Solution

  - by gfoley

  Our current project has ran into a circular dependency issue. Our business logic assembly is using classes and static methods from our SharedLibrary assembly. The SharedLibrary contains a whole bunch of helper functions, such as a SQL Reader class, Enumerators, Global Variables, Error Handling, Logging and Validation. The SharedLibrary needs access to the Business objects, but the Business objects need access to SharedLibrary. The old developers solved this obvious code smell by replicating the functionality of the business objects in the shared library (very anti-DRY). I've spent a day now trying to read about my options to solve this but i'm hitting a dead end. I'm open to the idea of architecture redesign, but only as a last resort. So how can i have a Shared Helper Library which can access the business objects, with the business objects still accessing the Shared Helper Library?

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• Working with foreigh keys - cannot insert

  - by Industrial

  Hi everyone! Doing my first tryouts with foreign keys in a mySQL database and are trying to do a insert, that fails for this reason: Integrity constraint violation: 1452 Cannot add or update a child row: a foreign key constraint fails Does this mean that foreign keys restrict INSERTS as well as DELETES and/or UPDATES on each table that is enforced with foreign keys relations? Thanks!

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• Need help choosing database server

  - by The Pretender

  Good day everyone. Recently I was given a task to develop an application to automate some aspects of stocks trading. While working on initial architecture, the database dilemma emerged. What I need is a fast database engine which can process huge amounts of data coming in very fast. I'm fairly experienced in general programming, but I never faced a task of developing a high-load database architecture. I developed a simple MSSQL database schema with several many-to-many relationships during one of my projects, but that's it. What I'm looking for is some advice on choosing the most suitable database engine and some pointers to various manuals or books which describe high-load database development. Specifics of the project are as follows: OS: Windows NT family (Server 2008 / 7) Primary platform: .NET with C# Database structure: one table to hold primary items and two or three tables with foreign keys to the first table to hold additional information. Database SELECT requirements: Need super-fast selection by foreign keys and by combination of foreign key and one of the columns (presumably DATETIME) Database INSERT requirements: The faster the better :) If there'll be significant performance gain, some parts can be written in C++ with managed interfaces to the rest of the system. So once again: given all that stuff I just typed, please give me some advice on what the best database for my project is. Links or references to some manuals and books on the subject are also greatly appreciated. EDIT: I'll need to insert 3-5 rows in 2 tables approximately once in 30-50 milliseconds and I'll need to do SELECT with 0-2 WHERE clauses queries with similar rate.

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• in google analytics, how do I get the site from the AccountEntry ?

  - by Chez

  in google analytics, how do I get the site from the AccountEntry ? looks like that if I do: entry.getProperty("ga:accountName") entry.getTitle().getPlainText() I get it. but is this correct ? where is it documented ?

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• CSS and Page Size and Horizontal Scrollbar

  - by Steve

  When I added some CSS stuff to my page, the page got wider and and horizontal appeared even the content is very minimal and does not require to scroll. How can I remove it. I used the following to remove it but it appears as a hack and I am just playing around with CSS, so is there a proper way to do this

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• Export multiple values from a single Combo Box? (Adobe Acrobat)

  - by metashockwave

  I'm trying to export 2 values from every single item from the combo box field. I have found two methods to insert items into a combo box: 1) insertItemAt http://www.verypdf.com/document/acrobat-forms-javascript/pg_0048.htm 2) setItems http://livedocs.adobe.com/acrobat_sdk/9/Acrobat9_HTMLHelp/wwhelp/wwhimpl/common/html/wwhelp.htm?context=Acrobat9_HTMLHelp&file=JS_API_AcroJS.88.748.html but neither method allows two parameters (im always get "missing ) after argument list" error from the Acrobat JavaScript Debugger) Does anyone know of a better solution for this problem? Thanks!

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• should I ever put a major version number into a C#/Java namespace?

  - by Andrew Patterson

  I am designing a set of 'service' layer objects (data objects and interface definitions) for a WCF web service (that will be consumed by third party clients i.e. not in-house, so outside my direct control). I know that I am not going to get the interface definition exactly right - and am wanting to prepare for the time when I know that I will have to introduce a breaking set of new data objects. However, the reality of the world I am in is that I will also need to run my first version simultaneously for quite a while. The first version of my service will have URL of http://host/app/v1service.svc and when the times comes by new version will live at http://host/app/v2service.svc However, when it comes to the data objects and interfaces, I am toying with putting the 'major' version of the interface number into the actual namespace of the classes. namespace Company.Product.V1 { [DataContract(Namespace = "company-product-v1")] public class Widget { [DataMember] string widgetName; } public interface IFunction { Widget GetWidgetData(int code); } } When the time comes for a fundamental change to the service, I will introduce some classes like namespace Company.Product.V2 { [DataContract(Namespace = "company-product-v2")] public class Widget { [DataMember] int widgetCode; [DataMember] int widgetExpiry; } public interface IFunction { Widget GetWidgetData(int code); } } The advantages as I see it are that I will be able to have a single set of code serving both interface versions, sharing functionality where possible. This is because I will be able to reference both interface versions as a distinct set of C# objects. Similarly, clients may use both interface versions simultaneously, perhaps using V1.Widget in some legacy code whilst new bits move on to V2.Widget. Can anyone tell why this is a stupid idea? I have a nagging feeling that this is a bit smelly.. notes: I am obviously not proposing every single new version of the service would be in a new namespace. Presumably I will do as many non-breaking interface changes as possible, but I know that I will hit a point where all the data modelling will probably need a significant rewrite. I understand assembly versioning etc but I think this question is tangential to that type of versioning. But I could be wrong.

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• How implement the Open Session in View pattern in NHibernate?

  - by MCardinale

  I'm using ASP.NET MVC + NHibernate + Fluent NHibernate and having a problem with lazy loading. Through this question (http://stackoverflow.com/questions/2519964/how-to-fix-a-nhibernate-lazy-loading-error-no-session-or-session-was-closed), I've discovered that I have to implement the Open Session in View pattern , but I don't know how. In my repositories classes, I use methods like this public ImageGallery GetById(int id) { using(ISession session = NHibernateSessionFactory.OpenSession()) { return session.Get<ImageGallery>(id); } } public void Add(ImageGallery imageGallery) { using(ISession session = NHibernateSessionFactory.OpenSession()) { using(ITransaction transaction = session.BeginTransaction()) { session.Save(imageGallery); transaction.Commit(); } } } And this is my Session Factory helper class: public class NHibernateSessionFactory { private static ISessionFactory _sessionFactory; private static ISessionFactory SessionFactory { get { if(_sessionFactory == null) { _sessionFactory = Fluently.Configure() .Database(MySQLConfiguration.Standard.ConnectionString(MyConnString)) .Mappings(m => m.FluentMappings.AddFromAssemblyOf<ImageGalleryMap>()) .ExposeConfiguration(c => c.Properties.Add("hbm2ddl.keywords", "none")) .BuildSessionFactory(); } return _sessionFactory; } } public static ISession OpenSession() { return SessionFactory.OpenSession(); } } Someone could help me to implements Open Session in View pattern? Thank you.

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