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• Tiling Problem Solutions for Various Size "Dominoes"

  - by user67081

  I've got an interesting tiling problem, I have a large square image (size 128k so 131072 squares) with dimensons 256x512... I want to fill this image with certain grain types (a 1x1 tile, a 1x2 strip, a 2x1 strip, and 2x2 square) and have no overlap, no holes, and no extension past the image boundary. Given some probability for each of these grain types, a list of the number required to be placed is generated for each. Obviously an iterative/brute force method doesn't work well here if we just randomly place the pieces, instead a certain algorithm is required. 1) all 2x2 square grains are randomly placed until exhaustion. 2) 1x2 and 2x1 grains are randomly placed alternatively until exhaustion 3) the remaining 1x1 tiles are placed to fill in all holes. It turns out this algorithm works pretty well for some cases and has no problem filling the entire image, however as you might guess, increasing the probability (and thus number) of 1x2 and 2x1 grains eventually causes the placement to stall (since there are too many holes created by the strips and not all them can be placed). My approach to this solution has been as follows: 1) Create a mini-image of size 8x8 or 16x16. 2) Fill this image randomly and following the algorithm specified above so that the desired probability of the entire image is realized in the mini-image. 3) Create N of these mini-images and then randomly successively place them in the large image. Unfortunately there are some downfalls to this simplification. 1) given the small size of the mini-images, nailing an exact probability for the entire image is not possible. Example if I want p(2x1)=P(1x2)=0.4, the mini image may only give 0.41 as the closes probability. 2) The mini-images create a pseudo boundary where no overlaps occur which isn't really descriptive of the model this is being used for. 3) There is only a fixed number of mini-images so i'm not sure how random this really is. I'm really just looking to brainstorm about possible solutions to this. My main concern is really to nail down closer probabilities, now one might suggest I just increase the mini-image size. Well I have, and it turns out that in certain cases(p(1x2)=p(2x1)=0.5) the mini-image 16x16 isn't even iteratively solvable.. So it's pretty obvious how difficult it is to randomly solve this for anything greater than 8x8 sizes.. So I'd love to hear some ideas. Thanks

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• Storing images in file system and returning URLs or virtually resizing and returning byte arrays?

  - by ismaelf

  I need to create a REST web service to manage user submitted images and displaying them all in a website. There are multiple websites that are going to use this service to manage and display images. The requirements are to have 5 pre-defined image sizes available. The 2 options I see are the following: The web service will create the 5 images, store them in the file system and and store the URL's in the database when the user submits the image. When the image is requested, the web service will return an array of URLs. I see this option to be a little hard on the hard drive. The estimates are 10,000 users per site, and lets say, 100 sites. The heavy processing will be done when the user submits the image and each image is going to be pulled from the File System. The web service will store just the image that the user submits in the file system and it's URL in the database. When the user request images, the web service will get the info from the DB, load the image on memory, create its 5 instances and return an object with 5 image arrays (I will probably cache the arrays). This option is harder on the processor and memory. The heavy processing will be done when the images get requested. A plus I see for option 2 is that it will give me the option to rewrite the URL of the image and make them site dependent (prettier) than having a image repository for all websites. But this is not a big deal. What do you think of these options? Do you have any other suggestions?

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• Implementing `let` without using a macro

  - by Matt Fenwick

  I'm learning Lisp, and I've just gotten to let, which I don't quite understand (the implementation of). A common definition for it is given in terms of lambda as a macro. However, nowhere have I seen that let must be implemented as a macro or in terms of lambda. Is it possible to define let without using a macro or lambda? I know it can be implemented as a primitive, but I want to know whether it can be implemented in Lisp without creating a macro -- by creating a special form or a function.

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• Should I always encapsulate an internal data structure entirely?

  - by Prog

  Please consider this class: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThings(){ return things; } } This class exposes the array it uses to store data, to any client code interested. I did this in an app I'm working on. I had a ChordProgression class that stores a sequence of Chords (and does some other things). It had a Chord[] getChords() method that returned the array of chords. When the data structure had to change (from an array to an ArrayList), all client code broke. This made me think - maybe the following approach is better: class ClassA{ private Thing[] things; // stores data // stuff omitted public Thing[] getThing(int index){ return things[index]; } public int getDataSize(){ return things.length; } public void setThing(int index, Thing thing){ things[index] = thing; } } Instead of exposing the data structure itself, all of the operations offered by the data structure are now offered directly by the class enclosing it, using public methods that delegate to the data structure. When the data structure changes, only these methods have to change - but after they do, all client code still works. Note that collections more complex than arrays might require the enclosing class to implement even more than three methods just to access the internal data structure. Is this approach common? What do you think of this? What downsides does it have other? Is it reasonable to have the enclosing class implement at least three public methods just to delegate to the inner data structure?

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• What patterns book for iOS development contains this specific information? [closed]

  - by Brett Ryan

  I've read several books on iOS development and Objective-C, however what a lot of them teach is how to work with interfaces and all contain the model inside the view controller, i.e. a UITableViewController based view will simply have an NSArray as it's model. I'm interested in what the best practices are for designing the structure of an application. Specifically I'm interested in best practices for the following: How to separate a model from the view controller. I think I know how to do this by simply replacing the NSArray style example with a specific model object, however what I do not know how to do is alert the view when the model changes. For example in .NET I would solve this by conforming to INotifyPropertyChanged and databinding, and similarly with Java I would use PropertyChangeListener. How to create a service model for my domain objects. For example I want to learn the best way to create a service for a hypothetical Widget object to manage an internal DB and also services for communicating with remote endpoints. I need to learn the best ways to do this in a way that interface components can subscribe to events such as widgetUpdated. These services should be singleton classes and some how dependency injected into model/controller objects. Books I've read so far are: Programming in Objective-C (4th Edition) Beginning iOS 5 Development: Exploring the iOS SDK The iOS 5 Developer's Cookbook: Expanded Electronic Edition: Essentials and Advanced Recipes for iOS Programmers Learn Objective-C on the Mac: For OS X and iOS I've also purchased the following updated books but not yet read them. The Core iOS 6 Developer's Cookbook (4th edition Programming in Objective-C (5th Edition) I come from a Java and C# background with 15 years experience, I understand that many of the ways I would do things in these languages may not fit to the ObjC way of developing applications. Would someone be able to provide me with the book on this topic containing this specific subject matter?

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• IXRepository and test problems

  - by Ridermansb

  Recently had a doubt about how and where to test repository methods. Let the following situation: I have an interface IRepository like this: public interface IRepository<T> where T: class, IEntity { IQueryable<T> Query(Expression<Func<T, bool>> expression); // ... Omitted } And a generic implementation of IRepository public class Repository<T> : IRepository<T> where T : class, IEntity { public IQueryable<T> Query(Expression<Func<T, bool>> expression) { return All().Where(expression).AsQueryable(); } } This is an implementation base that can be used by any repository. It contains the basic implementation of my ORM. Some repositories have specific filters, in which case we will IEmployeeRepository with a specific filter: public interface IEmployeeRepository : IRepository<Employee> { IQueryable<Employee> GetInactiveEmployees(); } And the implementation of IEmployeeRepository: public class EmployeeRepository : Repository<Employee>, IEmployeeRepository // TODO: I have a dependency with ORM at this point in Repository<Employee>. How to solve? How to test the GetInactiveEmployees method { public IQueryable<Employee> GetInactiveEmployees() { return Query(p => p.Status != StatusEmployeeEnum.Active || p.StartDate < DateTime.Now); } } Questions Is right to inherit Repository<Employee>? The goal is to reuse code once all implementing IRepository already been made. If EmployeeRepository inherit only IEmployeeRepository, I have to literally copy and paste the code of Repository<T>. In our example, in EmployeeRepository : Repository<Employee> our Repository lies in our ORM layer. We have a dependency here with our ORM impossible to perform some unit test. How to create a unit test to ensure that the filter GetInactiveEmployees return all Employees in which the Status != Active and StartDate < DateTime.Now. I can not create a Fake/Mock of IEmployeeRepository because I would be testing? Need to test the actual implementation of GetInactiveEmployees. The complete code can be found on Github

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• More Tables or More Databases?

  - by BuckWoody

  I got an e-mail from someone that has an interesting situation. He has 15,000 customers, and he asks if he should have a database for their data per customer. Without a LOT more data it’s impossible to say, of course, but there are some general concepts to keep in mind. Whenever you’re segmenting data, it’s all about boundary choices. You have not only boundaries around how big the data will get, but things like how many objects (tables, stored procedures and so on) that will be involved, if there are any cross-sections of data (do they share location or product information) and – very important – what are the security requirements? From the answer to these types of questions, you now have the choice of making multiple tables in a single database, or using multiple databases. A database carries some overhead – it needs a certain amount of memory for locking and so on. But it has a very clean boundary – everything from objects to security can be kept apart. Having multiple users in the same database is possible as well, using things like a Schema. But keeping 15,000 schemas can be challenging as well. My recommendation in complex situations like this is similar to a post on decisions that I did earlier – I lay out the choices on a spreadsheet in rows, and then my requirements at the top in the columns. I  give each choice a number based on how well it meets each requirement. At the end, the highest number wins. And many times it’s a mix – perhaps this person could segment customers into larger regions or districts or products, in a database. Within that database might be multiple schemas for the customers. Of course, he needs to query across all customers, that becomes another requirement. Share this post: email it! | bookmark it! | digg it! | reddit! | kick it! | live it!

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• What are the advantages of storing xml in a relational database?

  - by Chris

  I was poking around the AdventureWorks database today and I noticed that a number of tables (HumanResources.JobCandidate and Sales.Individual for example) have a column which is storing xml data. What I would to know is, what is the advantage of storing basically a database table row's worth of data in another table's column? Doesn't this make it difficult to query off of this information? Or is the assumption that the data won't need to be queried and just needs to be stored?

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• Is there a standard for machine-readable descriptions of RESTful services?

  - by ecmendenhall

  I've interacted with a few RESTful APIs that provided excellent documentation for humans and descriptive URIs, but none of them seem to return machine-readable descriptions of themselves. It's not too tough to write methods of my own that assemble the right paths, and many language-specific API libraries are already just wrappers around RESTful requests. But the next level of abstraction seems really useful: a library that could read in an API's own machine readable documentation and generate the wrappers automatically, perhaps with a call to some standard URI like base_url + '/documentation' Are there any standards for machine-readable API documentation? Am I doing REST wrong? I am a relatively new programmer, but this seems like a good idea.

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• Moving dozens of existing standalone retail sites to one central inventory database: what should I know going in?

  - by palintropos

  This will be the first project of this scale that I have attempted, and the first time I have run a website at all (much less dozens) using an off-site database. In particular, I'd like to know: what sort of optimizations I should read up on to make this run as smoothly as possible? any pitfalls/gotchas wiser, more experienced folk are aware of I should be on the lookout for, and what damage-control and preventative measures I should take against the nightmare scenario of the main server (hosting the database) having an outage, grinding over 100 websites to a halt (because they have no access to the product data).

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• Should static parameters in an API be part of each method?

  - by jschoen

  I am currently creating a library that is a wrapper for an online API. The obvious end goal is to make it as easy for others to use as possible. As such I am trying to determine the best approach when it comes to common parameters for the API. In my current situation there are 3 (consumer key, consumer secret, and and authorization token). They are essentially needed in every API call. My question is should I make these 3 parameters required for each method or is there a better way. I see my current options as being: Place the parameters in each method call public ApiObject callMethod(String consumerKey, String consumerSecret, String token, ...) This one seems reasonable, but seems awfully repetitive to me. Create a singleton class that the user must initialize before calling any api methods. This seems wrong, and would essentially limit them to accessing one account at a time via the API (which may be reasonable, I dunno). Make them place them in a properties file in their project. That way I can load the properties that way and store them. This seems similar to the singleton to me, but they would not have to explicitly call something to initialize these values. Is there another option I am not seeing, or a more common practice in this situation that I should be following?

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• Architecting persistence (and other internal systems). Interfaces, composition, pure inheritance or centralization?

  - by Vandell

  Suppose that you need to implement persistence, I think that you're generally limited to four options (correct me if I'm wrong, please) Each persistant class: Should implement an interface (IPersistent) Contains a 'persist-me' object that is a specialized object (or class) that's made only to be used the class that contains it. Inherit from Persistent (a base class) Or you can create a gigantic class (or package) called Database and make your persistence logic there. What are the advantages and problems that can come from each of one? In a small (5kloc) and algorithmically (or organisationally) simple app what is probably the best option?

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• Clarify the Single Responsibility Principle.

  - by dsimcha

  The Single Responsibility Principle states that a class should do one and only one thing. Some cases are pretty clear cut. Others, though, are difficult because what looks like "one thing" when viewed at a given level of abstraction may be multiple things when viewed at a lower level. I also fear that if the Single Responsibility Principle is honored at the lower levels, excessively decoupled, verbose ravioli code, where more lines are spent creating tiny classes for everything and plumbing information around than actually solving the problem at hand, can result. How would you describe what "one thing" means? What are some concrete signs that a class really does more than "one thing"?

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• Best way to manage a changelog

  - by Gnial0id

  I'm currently developing a WinForm application. In order to inform the client about the improvements and corrections made during the last version, I would like to manage and display a changelog. I mostly found existing changelog on website (the term changelog is pretty used) or explanation on how to manage the release numbers, which I don't care. So, these are my questions: Is there a good practice in changelog management (using XML, pure text in the app, etc.) in a desktop application ? What is the best way to display it (external website, inside the winform application) ? Thanks.

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• Draw "vision cone" / targetting element onto game world

  - by gkimsey

  I'm wanting to indicate various things using a "pie slice" sort of shape as below. Similar to vision cones in stealth game minimaps, or targetting indicators in RTS type games for frontal area attacks. Something generic enough to be used for both would be ideal. I need to be able to procedurally (and efficiently) change things like the slice width and length, color, transparency, position in the world, etc. For my particular situation, there's no concern with elevation, funky terrain, or really any third axis at all as far as this element is concerned. I have two first inclinations on how to accomplish this: 1) Manually generate the vertices for a main triangle, (possibly two, superimposed to get the border effect), a handful more to approximate the arc at the end, and roll it into a mesh. 2) Use some sort of 2D drawing library to create a circle and mask it off at the right angles, render to texture, and use that. For reference, I have some experience with Ogre3D, but I'm not attached to it as this is a mostly academic pursuit at the moment. Other technologies that might be better at accomplishing this are more than welcome. Finally, I'm kind of curious about how to do a "flashlight" or similar 3D effect that could produce the same result, but on all surfaces in the lit area.

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• What language(s) do I need to learn in order to develop an application like this?

  - by Josh

  I have an idea for making a web application. Ideally this application would have products which prices are increased each time a Retweet of the product at hand is made. Kind of like bids with tweets. Unfortunately my web development knowledge is very scarce. I know just basic HTML, virtually no CSS and that's it. I'm kindly asking for your insights on what you think would be best for making a web app like this. I have no good idea of where to start or what I need to get going. Your inputs are greatly appreciated. Thanks in advance.

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• Pattern for loading and handling resources

  - by Enoon

  Many times there is the need to load external resources into the program, may they be graphics, audio samples or text strings. Is there a patten for handling the loading and the handling of such resources? For example: should I have a class that loads all the data and then call it everytime I need the data? As in: GraphicsHandler.instance().loadAllData() ...//and then later: draw(x,y, GraphicsHandler.instance().getData(WATER_IMAGE)) //or maybe draw(x,y, GraphicsHandler.instance().WATER_IMAGE) Or should I assign each resource to the class where it belongs? As in (for example, in a game): Graphics g = GraphicsLoader.load(CHAR01); Character c = new Character(..., g); ... c.draw(); Generally speaking which of these two is the more robust solution? GraphicsHandler.instance().getData(WATER_IMAGE) //or GraphicsHandler.instance().WATER_IMAGE //a constant reference

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• I know of three ways in which SRP helps reduce coupling. Are there even more? [closed]

  - by user1483278

  I'd like to figure all the possible ways SRP helps us reduce coupling. Thus far I can think of three: 1) If class A has more than one responsibility, these responsibilities become coupled and as such changes to one of these responsibilities may require changes to other of A's responsibilities. 2) Related functionality usually needs to be changed for the same reason and by grouping it togerther in a single class, the changes can be made in as few places as possible ( at best changes only need be made to the class which groups together these functionalities) 3) Assuming class A performs two tasks ( thus may change for two reasons ), then number of classes utilising A will be greater than if A performed just a single task ( reason being that some classes will need A to perform first task, other will need A for second task, and still others will utilise it for both tasks ).This also means that when A breaks, the number of classes ( utilising A ) being impaired will be greater than if A performed just a single task. Can SRP also help reduce coupling in any other way, not described above? Thank you

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• Accepting a numerical range in a function call

  - by dekpos

  I have encountered two ways of doing it: void foo(int from, int to); /* 'from' inclusive, 'to' exclusive */ void foo(int startIndex, int rangelength); Has one style historically been preferred over the other? If so, was it just a matter of convention or was it due to some deeper underlying reason? I'm currently programming in Java and noticed that the Arrays class uses the former style. The exclusivity of the to argument felt somewhat unintuitive to me, which led me to ask this question.

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• JS / HTML 5 Compatablity issue on iOS 6

  - by Dhaval

  I'm using HTML 5 to play video and there are some content before the video so I'm using flexroll to scroll that whole window. I'm checking it on iPad, now problem is that in iOS 5 its working fine but when I update to iOS 6 then screen is not scrolling only video is scroll up and down, content is as it is in the position. I can't understand what is the exact problem. Is that js compatibility issue or HTML 5 video compatibility issue. Can anyone please help me to figure out, your help will really be appreciated.

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• How to calculate production when player is offline

  - by Kaizer

  What is the best way to do for example food growth based on how many food buildings you have? Lets say I have a webbased game where you can build a farm wich generates 60 food units per hour. A player has 1 farm in his possession. What is the best way to keep on producing these units even when the player is offline? Should I do the math when the player get's back online again? If so..how can I do this without having to save his last online time every 5 seconds so I can do some maths with it when he logs back in (datetime.now - lastonlinetime)? Next thing is when the player is online, should I refresh his resource count every 5 seconds or so by going to the database and back? This would seem weird to do for every logged on player. I hope you understand my question. kind regards

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• Mobile Compatibility: traditional website look vs native application ?

  - by Siddiqui

  I have a question related to mobile compatible websites, I have seen two type of websites One in which they adopt traditional website look and adjust website according to mobile screen, if they have lot of information which can not be adjust according to screen then they expand the height of page, so that user can scroll the page to see more information... In the second approach they used native application look means use navigation-bar, tab-bar, tool-bar, scroll-view just like in native applications. Height and width of page adjust according to screen size, if they have more information then they use scroll-view etc... My question is: which approach is better then other, in which approach you feel more comfortable to use website.

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• What is the most concise, unambiguous syntax for operator associated methods (for overloading etc.) that doesn't pollute the namespace?

  - by Doug Treadwell

  Python tends to add double underscores before its built-in or overloadable operator methods, like __add(), whereas C++ requires declaring overloaded operators as operator + (Thing& thing) { /* code */ } for example. Personally I like the operator syntax because it seems to be more explicit and keeps these operator overloading methods separated from other methods without introducing weird prefix notation. What are your thoughts? Also, what about the case of built-in methods that are needed for the programming language to work properly? Is name mangling (like adding __ prefix or sys or something) the best solution here? What do you think about having another type of method declaration, like ... "system method" for lack of creativity at the moment. So there would be two kinds of declarations: int method_name() { ... } system int method_name() { ... } ... and the call would need to be different to distinguish between them. obj.method_name(); vs obj:method_name(); perhaps, assuming a language where : can be unambiguously used in this situation. obj.method_name() vs obj.(system method_name)() Sure, the latter is ugly, but the idea is to make the common case simple and system stuff should be kept out of the way. Maybe the Objective-C notation of method calls? [obj method_name]? Are there more alternatives? Please make suggestions.

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• Android Bitmap: Collision Detecting

  - by Aekasitt Guruvanich

  I am writing an Android game right now and I would need some help in the collision of the Pawns on screen. I figured I could run a for loop on the Player class with all Pawn objects on the screen checking whether or not Width*Height intersects with each other, but is there a more efficient way to do this? And if you do it this way, many of the transparent pixel inside the rectangular area will also be considered as collision as well. Is there a way to check for collision between Bitmap on a Canvas that disregard transparent pixels? The class for player is below and the Pawn class uses the same method of display. Class Player { private Resources res; // Used for referencing Bitmap from predefined location private Bounds bounds; // Class that holds the boundary of the screen private Bitmap image; private float x, y; private Matrix position; private int width, height; private float velocity_x, velocity_y; public Player (Resources resources, Bounds boundary) { res = resources; bounds = boundary; image = BitmapFactory.decodeResource(res, R.drawable.player); width = image.getWidth(); height = image.getHeight(); position = new Matrix(); x = bounds.xMax / 2; // Initially puts the Player in the middle of screen y = bounds.yMax / 2; position.preTranslate(x,y); } public void draw(Canvas canvas) { canvas.drawBitmap(image, position, null); } }

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• How to implement a multi-part snake with smooth movement? [closed]

  - by Jamie

  Sorry that i couldnt answer on my previous post but it got closed. I couldnt answer because i had to prepair for my finals. As there were problems with understanding of what im trying to achieve, im going to describe a little bit more in depth. Im creating a game in which you steer a snake. I assume everybody knows how that works. But in my case the snake isnt just propagating in an array element by element. Imagine a 2Dgrid on which the snake moves. Its 10x10 tiles. Lets say one tile is 4x4 meters. The snakes head spawns in the middle of the (3,2) tile (beginning with (0,0)), so its position is (4*3+2,4*2+2)(the 2's are so that the snake is in the middle of the 4x4 tile). And heres where the fun begins. when the snake moves, it doesnt jump to next tile. Instead it moves a fraction of the way there. So lets say the snake is heading to tile (4,2). After it moved once, its position is (4*3+2+0.1,4*2+2), where 0.1 is the fraction of the way it moved. This is done to achieve smooth movement. So now im adding the rest of the body. The rest is supposed to move along the exact same path as the head did. I implemented it so that each part of the body has its own position and direction. Then i apply this algorithm: 1.Move each part in its direction. 2.If a part is in the middle of the tile(which implies all of them are), change each parts direction to the direction of the part proceeding it. As i said before i could make this work, but i cant stop thinking that im overlooking a much easier and cleaner solution. So this is my question. Is there any easier/better/faster way to do this?

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