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• PHP class data implementation

  - by Bakanyaka

  I'm studying OOP PHP and have watched two tutorials that implement user login\registration system as an example. But implementation varies. Which way will be more correct one to work with data such as this? Load all data retrieved from database as array into a property called something like _data on class creation and further methods operate with this property Create separate properties for each field retrieved from database, on class creation load all data fields into respective properties and operate with that properties separately? Then let's say I want to create a method that returns a list of all users with their data. Which way is better? Method that returns just an array of userdata like this: Array([0]=>array([id] => 1, [username] => 'John', ...), [1]=>array([id] => 2, [username] => 'Jack', ...), ...) Method that creates a new instance of it's class for each user and returns an array of objects

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• Is this a valid implementation of the repository pattern?

  - by user1578653

  I've been reading up about the repository pattern, with a view to implementing it in my own application. Almost all examples I've found on the internet use some kind of existing framework rather than showing how to implement it 'from scratch'. Here's my first thoughts of how I might implement it - I was wondering if anyone could advise me on whether this is correct? I have two tables, named CONTAINERS and BITS. Each CONTAINER can contain any number of BITs. I represent them as two classes: class Container{ private $bits; private $id; //...and a property for each column in the table... public function __construct(){ $this->bits = array(); } public function addBit($bit){ $this->bits[] = $bit; } //...getters and setters... } class Bit{ //some properties, methods etc... } Each class will have a property for each column in its respective table. I then have a couple of 'repositories' which handle things to do with saving/retrieving these objects from the database: //repository to control saving/retrieving Containers from the database class ContainerRepository{ //inject the bit repository for use later public function __construct($bitRepo){ $this->bitRepo = $bitRepo; } public function getById($id){ //talk directly to Oracle here to all column data into the object //get all the bits in the container $bits = $this->bitRepo->getByContainerId($id); foreach($bits as $bit){ $container->addBit($bit); } //return an instance of Container } public function persist($container){ //talk directly to Oracle here to save it to the database //if its ID is NULL, create a new container in database, otherwise update the existing one //use BitRepository to save each of the Bits inside the Container $bitRepo = $this->bitRepo; foreach($container->bits as $bit){ $bitRepo->persist($bit); } } } //repository to control saving/retrieving Bits from the database class BitRepository{ public function getById($id){} public function getByContainerId($containerId){} public function persist($bit){} } Therefore, the code I would use to get an instance of Container from the database would be: $bitRepo = new BitRepository(); $containerRepo = new ContainerRepository($bitRepo); $container = $containerRepo->getById($id); Or to create a new one and save to the database: $bitRepo = new BitRepository(); $containerRepo = new ContainerRepository($bitRepo); $container = new Container(); $container->setSomeProperty(1); $bit = new Bit(); $container->addBit($bit); $containerRepo->persist($container); Can someone advise me as to whether I have implemented this pattern correctly? Thanks!

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• What class structure allows for a base class and mix/match of subclasses? (Similar to Users w/ roles)

  - by cdeszaq

  I have a set of base characteristics, and then a number of sub-types. Each instance must be one of the sub-types, but can be multiple sub-types at once. The sub-types of each thing can change. In general, I don't care what subtype I have, but sometimes I do care. This is much like a Users-Roles sort of relationship where a User having a particular Role gives the user additional characteristics. Sort of like duck-typing (ie. If my Foo has a Bar, I can treat it like a ThingWithABar.) Straight inheritance doesn't work, since that doesn't allow mix/match of sub-types. (ie. no multi-inheritance). Straight composition doesn't work because I can't switch that up at runtime. How can I model this?

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• Is there a language that allows this syntax: add(elements)at(index);

  - by c_maker

  Does a language exist with such a syntax? If not, what are some of the limitations/disadvantages to this syntax in case I want to write a language that supported it? Some examples: sort(array, fromIndex, toIndex); vs sort(array)from(index1)to(index2); Method signature would like this: sort(SomeType[] arr)from(int begin)to(int end){ ... } Update: Because there might be some confusion, I'd like to clarify... I meant this question as a general idea like this (not specific to sorting and possibly using keywords like from and to): In JAVA(like language): void myfancymethod(int arg1, String arg2){ ... } myfancymethod(1, "foo"); In imaginary language: void my(int arg1)fancy(String arg2)method{ ... } my(1)fancy("foo")method;

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• Significant amount of the time, I can't think of a reason to have an object instead of a static class. Do objects have more benefits than I think?

  - by Prog

  I understand the concept of an object, and as a Java programmer I feel the OO paradigm comes rather naturally to me in practice. However recently I found myself thinking: Wait a second, what are actually the practical benefits of using an object over using a static class (with proper encapsulation and OO practices)? I could think of two benefits of using an object (both significant and powerful): Polymorphism: allows you to swap functionality dynamically and flexibly during runtime. Also allows to add new functionality 'parts' and alternatives to the system easily. For example if there's a Car class designed to work with Engine objects, and you want to add a new Engine to the system that the Car can use, you can create a new Engine subclass and simply pass an object of this class into the Car object, without having to change anything about Car. And you can decide to do so during runtime. Being able to 'pass functionality around': you can pass an object around the system dynamically. But are there any more advantages to objects over static classes? Often when I add new 'parts' to a system, I do so by creating a new class and instantiating objects from it. But recently when I stopped and thought about it, I realized that a static class would do just the same as an object, in a lot of the places where I normally use an object. For example, I'm working on adding a save/load-file mechanism to my app. With an object, the calling line of code will look like this: Thing thing = fileLoader.load(file); With a static class, it would look like this: Thing thing = FileLoader.load(file); What's the difference? Fairly often I just can't think of a reason to instantiate an object when a plain-old static-class would act just the same. But in OO systems, static classes are fairly rare. So I must be missing something. Are there any more advantages to objects other from the two that I listed? Please explain.

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• Versioning Java APIs in a non-web context

  - by GAP

  I have modular java application which consists of 40 modules. Some of these modules needs to expose external APIs which other modules or any external integration should be using. The system runs as a desktop application and each module is bundled as a separate jar file. My plan is to bundle the external api as a separate jar. But now the question is: how can I maintain multiple versions of the same API to keep backward compatibility in cases where it can co-exist? Are there any de facto standards on handling APIs versioning out of a web context ?

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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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• "Do it right, against customer's wishes" - how is it called?

  - by SF.

  We know the optimal situation of negotiating corrections of specifications with the customer, getting the specs to do what the client wanted, not what they said or thought they wanted. That's negotiating, explaining. Sometimes, we're unable to convince the client. We're forced to produce broken as designed. This, called "demonology" by merit of mages summoning demons and demons fulfilling their wishes very literally, causing the mage's demise as result, is another approach that will leave the customer very dissatisfied once they realize their error, and of course try to pin the blame on the developer. Now I just faced a very different approach: the customer created simple specs that fail to account for some critical caveat, and is completely unwilling to fix them, admit the obvious errors and accept suggested corrections. The product made to these specs will be critically broken, and possibly might cost human lives. Still, it's too late to drop the contract entirely. The contract has punitive clauses for that, ones we can't really accept. The boss' decision? We do the work right and lie to the customer that we did it according to the specs. The algorithms in question are hidden deep enough under the surface, the product will do the work just fine, won't fail in the caveat situation, and unless someone digs too deep, they will never discover we didn't break it as requested. Is there some common name for this tactics of execution of specs?

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• Any tips/tricks/resources on actually TEACHING a class on OOP? [closed]

  - by Sempus

  I may slowly be getting into teaching an Object-Orientated Programming class at my school in a year or two. I just graduated and work at my school as an Application Programmer. I'd first start off as a TA/grader and then slowly move into the Professor role. The class would be in Java. I always see resources on this fine site about HOW to program, but does anyone know any tips/tricks/resources on how to TEACH a programming class? It would be full of all different skills levels(but still semi-technical) so it would have to be a little more understandable than if it was just CS kids.

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• Requiring a specific order of compilaiton

  - by Aber Kled

  When designing a compiled programming language, is it a bad idea to require a specific order of compilation of separate units, according to their dependencies? To illustrate what I mean, consider C. C is the opposite of what I'm suggesting. There are multiple .c files, that can all depend on each other, but all of these separate units can be compiled on their own, in no particular order - only to be linked together into a final executable later. This is mostly due to header files. They enable separate units to share information with each other, and thus the units are able to be compiled independently. If a language were to dispose of header files, and only keep source and object files, then the only option would be to actually include the unit's meta-information in the unit's object file. However, this would mean that if the unit A depends on the unit B, then the unit B would need to be compiled before unit A, so unit A could "import" the unit B's object file, thus obtaining the information required for its compilation. Am I missing something here? Is this really the only way to go about removing header files in compiled languages?

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• Do I need to add an index on a table with one row?

  - by briddums

  I'm creating a parameter table in our database. This table will have 1 row with values that are environment specific (production, development, etc). Is there any reason why I should define an index on this table? Update This table is a parameter table which will be used to drive our job queue system. The table will be defined like this: QueuePrm LogLvl integer ShowMs boolean Restart boolean This table will only ever have 1 row. No other table in our system will reference it.

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• How is this paradigm/style called?

  - by McMannus

  I have the following situation: I'm developing an add-in for a UML modeling tool. The models that can be created by the user are stored inside the main application and a limited access to the models is given through its API. However, the add-in has a lot of callbacks for events that are triggered by the main application, when changes to the model occur by the user. Since the models are already stored once in the main application, I considered it not practicable to duplicate the models in the add-in, which leads to the fact that I have only behavior in the add-in, rather than having a state. This behavior is mainly expressed by static functions, that are organized in functional cohesive classes. The callbacks for the events have always references to the model elements relevant for the specifc event that ocurred. First, it seemed to me that this is a procedural style in general, but procedural style doesn't consider events/callbacks, so this boils down to the question. How is this programming style called?

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• Architecture driven by users, or by actions/content?

  - by hugerth

  I have a question about designing MVC app architecture. Let's say our application has three main categories of views (items of type 1, items of type 2...). And we have three (or more in future) types of users - Admins, let's say Moderators and typical Users. And in the future there might be more of them. Admins have full access to app, Moderators can visit only 2/3 type of items, and Users can visit only basic type of items. Should I divide my controllers/views/whatever like this: Items "A", Items "B", Items "C", then make them 100% finished and at the end add access privileges? Pros: DRY option Cons Conditional expressions in views Or another options: Items "A" / Admin, Items "A" / Moderator / Items "B" Admin ...? Pros: Divided parts of application for specific user (is that pros?) Cons: A lot of repeated code I don't have great experience in planning such things so it would nice if you can give me some tips or links to learn something about it.

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• How to create a manager class without global variables nor singletons?

  - by Omega

  I would like to implement some kind of manager class in my application. It will be in charge of loading textures, processing them, distributing them etc... At first, I wanted to make a global variable that simply contains an instance of my manager class. I found this question: http://stackoverflow.com/questions/4646577/global-variables-in-java. However, the users there seem to recommend to never use global variables. Fine then, I once heard about Singletons, so I though I could use that instead. I mean, creating just one instance of my manager class sounds good. However, I found this other question: When is Singleton appropriate?, which basically tells me that Singletons are, in most scenarios, some kind of anti-pattern. Now I am a bit lost - what other approach can I take to create my manager class, whose only requirement is to be accessible from anywhere?

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• how to stop enemies from moving to one point when lots of them are chasing one object [duplicate]

  - by BBgun

  This question already has an answer here: Is there a simple way to stop enemies standing in the same spot? 8 answers i am making a top down game which lots of enemies are chasing one guy. then,enemies would move to one point without any collision,they just overlay each other. so ,is there any simple way to make them feel more real? make them not overlay with each other? ================================= i have tried the solution using boundbox to check collision, but i still very puzzled about what to do with the collision. i have a bad solution.it doesn't work well. my solution in simple: foreach(around_enemy_arr in other) { vector a = normalize(self.positionvector - other.positionvector); self.move_vector = self.move_vector + a; } this can work,but when plenty of enemies come very close to each other,they would shake. i am sooooo confused. please help.

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• Characteristics, what's the inverse of (x*(x+1))/2? [closed]

  - by Valmond

  In my game you can spend points to upgrade characteristics. Each characteristic has a formula like: A) out = in : for one point spent, one pont gained (you spend 1 point on Force so your force goes from 5 to 6) B) out = last level (starting at 1) : so the first point spent earns you 1 point, the next point spent earns you an additional 2 and so on (+3,+4,+5...) C) The inverse of B) : You need to spend 1 point to earn one, then you need to spend 2 to earn another one and so on. I have already found the formula for calculating the actual level of B when points spent = x : charac = (x*(x+1))/2 But I'd like to know what the "reverse" version of B) (usable for C) is, ie. if I have spent x points, how many have I earned if 1 spent gives 1, 1+2=3 gives 2, 1+2+3=6 gives 3 and so on. I know I can just calculate the numbers but I'd like to have the formula because its neater and so that I can stick it in an excel sheet for example... Thanks! ps. I think I have nailed it down to something like charac = sqrt( x*m +k) but then I'm stuck doing number guessing for k and m and I feel I might be wrong anyway as I get close but never hits the spot.

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• VMware vSphere cluster design for site redundancy

  - by Stefan Radovanovici

  I have a question about the best design for site redudancy when using vSphere clusters. A bit of background info about our situation first though. We are a medium-sized company with two main offices, located in different countries. Our networks are linked by a Layer2 150Mbps leased line which is currently underused. We have a variety of services running for internal use within the company, some on physycal servers and some on existing vSphere clusters. In our department we also run several services (almost all running under various forms of Linux) like NTP, Syslog, jump servers, monitoring servers and so on. We have now the requirement that those servers need to be redundant within each location (which they are not at the moment) and also site redudant (which they are to some extent, the servers are duplicated in the 2nd location with configurations kept in sync via various methods at the application layer). There is no SAN available for us, at least not something that we can use at the moment. Cost is also an issue. While we do have some budget available for this, we can't afford to buy SANs for both locations for example. I looked at the VSA feature and it seems that this could be something for us but I am unsure how to solve the site-redudancy requirement. At the moment for testing purposes I am setting up in a lab a vSphere 5 with VSA on two ESXi hosts. I am currently using the Essentials Plus kit with VSA license, which allows me to build a VSA cluster on up to 3 hosts, together with a vCenter license to manage them. The hosts each have two dual-port network cards and two 600GB drives, running in Raid1. Hardware-wise this will be enough for us to run the all the services we need as VMs and will provide redundandcy within the site. At the moment I see only two option to have site redundancy: build an identical VSA cluter in the second location and keep the various services sync'ed at application layer (database sync, rsync and so on). simply move one of the hosts from the existing cluster to the second location, basically having the VSA cluster span the 150Mbps link between the sites. I would very much prefer the second option but I am unsure how well it'll work, if it can work at all. Technically it should, we can span the needed VLANs across the leased line and have them available in the second location. The advantage would be that we don't need to worry at all about sync'ing databases and the like. But I have the feeling that the bandwidth will not be enough, I have no way of knowing how much traffic will the VSA cluster generate between the hosts. I realize that this will most likely depend on the individual usage of the VMs but still, I have no idea how VSA replicates data between the ESXi hosts. Are these my only options or can my goals be achieved in some other way ? Is there perhaps a way to have some sort of "cold stand by" cluster in the second location where the VMs would be sync'ed once per night from the main location ? The idea is that in case the first site becomes unavailable, we would be able to bring all those VMs online there. We would be ok with the data being 1 day old. Any answers are appreciated. Best regards, Stefan

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• [Java] RSA BadPaddingException : data must start with zero

  - by Robin Monjo

  Hello everyone. I try to implement an RSA algorithm in a Java program. I am facing the "BadPaddingException : data must start with zero". Here are the methods used to encrypt and decrypt my data : public byte[] encrypt(byte[] input) throws Exception { Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");// cipher.init(Cipher.ENCRYPT_MODE, this.publicKey); return cipher.doFinal(input); } public byte[] decrypt(byte[] input) throws Exception { Cipher cipher = Cipher.getInstance("RSA/ECB/PKCS1Padding");/// cipher.init(Cipher.DECRYPT_MODE, this.privateKey); return cipher.doFinal(input); } privateKey and publicKey attributes are read from files this way : public PrivateKey readPrivKeyFromFile(String keyFileName) throws IOException { PrivateKey key = null; try { FileInputStream fin = new FileInputStream(keyFileName); ObjectInputStream ois = new ObjectInputStream(fin); BigInteger m = (BigInteger) ois.readObject(); BigInteger e = (BigInteger) ois.readObject(); RSAPrivateKeySpec keySpec = new RSAPrivateKeySpec(m, e); KeyFactory fact = KeyFactory.getInstance("RSA"); key = fact.generatePrivate(keySpec); ois.close(); } catch (Exception e) { e.printStackTrace(); } return key; } Private key and Public key are created this way : public void Initialize() throws Exception { KeyPairGenerator keygen = KeyPairGenerator.getInstance("RSA"); keygen.initialize(2048); keyPair = keygen.generateKeyPair(); KeyFactory fact = KeyFactory.getInstance("RSA"); RSAPublicKeySpec pub = fact.getKeySpec(keyPair.getPublic(), RSAPublicKeySpec.class); RSAPrivateKeySpec priv = fact.getKeySpec(keyPair.getPrivate(), RSAPrivateKeySpec.class); saveToFile("public.key", pub.getModulus(), pub.getPublicExponent()); saveToFile("private.key", priv.getModulus(), priv.getPrivateExponent()); } and then saved in files : public void saveToFile(String fileName, BigInteger mod, BigInteger exp) throws IOException { FileOutputStream f = new FileOutputStream(fileName); ObjectOutputStream oos = new ObjectOutputStream(f); oos.writeObject(mod); oos.writeObject(exp); oos.close(); } I can't figured out how the problem come from. Any help would be appreciate ! Thanks in advance.

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• The Collatz Sequence problem

  - by Gandalf StormCrow

  I'm trying to solve this problem, its not a homework question, its just code I'm submitting to uva.onlinejudge.org so I can learn better java trough examples. Here is the problem sample input : 3 100 34 100 75 250 27 2147483647 101 304 101 303 -1 -1 Here is simple output : Case 1: A = 3, limit = 100, number of terms = 8 Case 2: A = 34, limit = 100, number of terms = 14 Case 3: A = 75, limit = 250, number of terms = 3 Case 4: A = 27, limit = 2147483647, number of terms = 112 Case 5: A = 101, limit = 304, number of terms = 26 Case 6: A = 101, limit = 303, number of terms = 1 The thing is this has to execute within 3sec time interval otherwise your question won't be accepted as solution, here is with what I've come up so far, its working as it should just the execution time is not within 3 seconds, here is code : import java.util.Scanner; class Main { public static void main(String[] args) { Scanner stdin = new Scanner(System.in); int start; int limit; int terms; int a = 0; while (stdin.hasNext()) { start = stdin.nextInt(); limit = stdin.nextInt(); if (start > 0) { terms = getLength(start, limit); a++; } else { break; } System.out.println("Case "+a+": A = "+start+", limit = "+limit+", number of terms = "+terms); } } public static int getLength(int x, int y) { int length = 1; while (x != 1) { if (x <= y) { if ( x % 2 == 0) { x = x / 2; length++; }else{ x = x * 3 + 1; length++; } } else { length--; break; } } return length; } } And yes here is how its meant to be solved : An algorithm given by Lothar Collatz produces sequences of integers, and is described as follows: Step 1: Choose an arbitrary positive integer A as the first item in the sequence. Step 2: If A = 1 then stop. Step 3: If A is even, then replace A by A / 2 and go to step 2. Step 4: If A is odd, then replace A by 3 * A + 1 and go to step 2. And yes my question is how can I make it work inside 3 seconds time interval?

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• Are there any working implementations of the rolling hash function used in the Rabin-Karp string sea

  - by c14ppy

  I'm looking to use a rolling hash function so I can take hashes of n-grams of a very large string. For example: "stackoverflow", broken up into 5 grams would be: "stack", "tacko", "ackov", "ckove", "kover", "overf", "verfl", "erflo", "rflow" This is ideal for a rolling hash function because after I calculate the first n-gram hash, the following ones are relatively cheap to calculate because I simply have to drop the first letter of the first hash and add the new last letter of the second hash. I know that in general this hash function is generated as: H = c1ak - 1 + c2ak - 2 + c3ak - 3 + ... + cka0 where a is a constant and c1,...,ck are the input characters. If you follow this link on the Rabin-Karp string search algorithm , it states that "a" is usually some large prime. I want my hashes to be stored in 32 bit integers, so how large of a prime should "a" be, such that I don't overflow my integer? Does there exist an existing implementation of this hash function somewhere that I could already use? Here is an implementation I created: public class hash2 { public int prime = 101; public int hash(String text) { int hash = 0; for(int i = 0; i < text.length(); i++) { char c = text.charAt(i); hash += c * (int) (Math.pow(prime, text.length() - 1 - i)); } return hash; } public int rollHash(int previousHash, String previousText, String currentText) { char firstChar = previousText.charAt(0); char lastChar = currentText.charAt(currentText.length() - 1); int firstCharHash = firstChar * (int) (Math.pow(prime, previousText.length() - 1)); int hash = (previousHash - firstCharHash) * prime + lastChar; return hash; } public static void main(String[] args) { hash2 hashify = new hash2(); int firstHash = hashify.hash("mydog"); System.out.println(firstHash); System.out.println(hashify.hash("ydogr")); System.out.println(hashify.rollHash(firstHash, "mydog", "ydogr")); } } I'm using 101 as my prime. Does it matter if my hashes will overflow? I think this is desirable but I'm not sure. Does this seem like the right way to go about this?

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• J: Self-reference in bubble sort tacit implementation

  - by Yasir Arsanukaev

  Hello people! Since I'm beginner in J I've decided to solve a simple task using this language, in particular implementing the bubblesort algorithm. I know it's not idiomatically to solve such kind of problem in functional languages, because it's naturally solved using array element transposition in imperative languages like C, rather than constructing modified list in declarative languages. However this is the code I've written: (((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # Let's apply it to an array: (((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # 5 3 8 7 2 2 3 5 7 8 The thing that confuses me is $: referring to the statement within the outermost parentheses. Help says that: $: denotes the longest verb that contains it. The other book (~ 300 KiB) says: 3+4 7 5*20 100 Symbols like + and * for plus and times in the above phrases are called verbs and represent functions. You may have more than one verb in a J phrase, in which case it is constructed like a sentence in simple English by reading from left to right, that is 4+6%2 means 4 added to whatever follows, namely 6 divided by 2. Let's rewrite my code snippet omitting outermost ()s: ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) ^: # 5 3 8 7 2 2 3 5 7 8 Reuslts are the same. I couldn't explain myself why this works, why only ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) is treated as the longest verb for $: but not the whole expression ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) ^: # and not just (<./@(2&{.)), $:@((>./@(2&{.)),2&}.), because if ((<./@(2&{.)), $:@((>./@(2&{.)),2&}.)) ^: (1<#) is a verb, it should also form another verb after conjunction with #, i. e. one might treat the whole sentence (first snippet) as a verb. Probably there's some limit for the verb length limited by one conjunction. Look at the following code (from here): factorial =: (* factorial@<:) ^: (1&<) factorial 4 24 factorial within expression refers to the whole function, i. e. (* factorial@<:) ^: (1&<). Following this example I've used a function name instead of $:: bubblesort =: (((<./@(2&{.)), bubblesort@((>./@(2&{.)),2&}.)) ^: (1<#)) ^: # bubblesort 5 3 8 7 2 2 3 5 7 8 I expected bubblesort to refer to the whole function, but it doesn't seem true for me since the result is correct. Also I'd like to see other implementations if you have ones, even slightly refactored. Thanks.

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• Drawing Bresenham’s Line- Algorithm in all quadrants

  - by Yoyo2965259

  I am newbie for OpenGL. I am practicing the exercises from my textbook but I could not get the outputs which is should be in Bresenham's Line Algorithm in all quadrants. Here's the coding: #include <Windows.h> #include <GL/glut.h> void init(void) { glClearColor(0.0, 0.0, 0.0, 0.0); glShadeModel(GL_FLAT); } void BresnCir(void) { int delta, deltadash; glClear(GL_COLOR_BUFFER_BIT); glPointSize(3.0); int r = 150; int x = 0; int y = r; int D = 2 * (1 - r); glBegin(GL_POINTS); do { glVertex2i(x, y); if (D < 0) { delta = 2 * D + 2 * y - 1; if (delta <= 0) { x++; Right(x); } else { x++; y--; Diagonal(x, y); } glVertex2i(x, y); } else { deltadash = 2 * D - 2 * x - 1; if (deltadash <= 0) { x++; y--; Diagonal(x, y); } else { y--; Down(y); } glVertex2i(x, y); } if (D == 0) { x++; y--; Diagonal(x, y); glVertex2i(x, y); } } while (y > 0); glEnd(); glFlush(); } int main(int argc, char** argv) { glutInit(&argc, argv); glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB); glutInitWindowSize(400, 150); glutInitWindowPosition(100, 100); glutCreateWindow(argv[0]); init(); glutDisplayFunc(BresnCir); glutMainLoop(); return 0; } But, it keep comes out with errors C3861.

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• Miller-rabin exception number?

  - by nightcracker

  Hey everyone. This question is about the number 169716931325235658326303. According to http://www.alpertron.com.ar/ECM.HTM it is prime. According to my miller-rabin implementation in python with 7 repetitions is is composite. With 50 repetitions it is still composite. With 5000 repetitions it is STILL composite. I thought, this might be a problem of my implementation. So I tried GNU MP bignum library, which has a miller-rabin primality test built-in. I tested with 1000000 repetitions. Still composite. This is my implementation of the miller-rabin primality test: def isprime(n, precision=7): if n == 1 or n % 2 == 0: return False elif n < 1: raise ValueError("Out of bounds, first argument must be > 0") d = n - 1 s = 0 while d % 2 == 0: d //= 2 s += 1 for repeat in range(precision): a = random.randrange(2, n - 2) x = pow(a, d, n) if x == 1 or x == n - 1: continue for r in range(s - 1): x = pow(x, 2, n) if x == 1: return False if x == n - 1: break else: return False return True And the code for the GMP test: #include <gmp.h> #include <stdio.h> int main(int argc, char* argv[]) { mpz_t test; mpz_init_set_str(test, "169716931325235658326303", 10); printf("%d\n", mpz_probab_prime_p(test, 1000000)); mpz_clear(test); return 0; } As far as I know there are no "exceptions" (which return false positives for any amount of repetitions) to the miller-rabin primality test. Have I stumpled upon one? Is my computer broken? Is the Elliptic Curve Method wrong? What is happening here? EDIT I found the issue, which is http://www.alpertron.com.ar/ECM.HTM. I trusted this applet, I'll contact the author his applet's implementation of the ECM is faulty for this number. Thanks. EDIT2 Hah, the shame! In the end it was something that went wrong with copy/pasting on my side. NOR the applet NOR the miller-rabin algorithm NOR my implementation NOR gmp's implementation of it is wrong, the only thing that's wrong is me. I'm sorry.

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• Finding what makes strings unique in a list, can you improve on brute force?

  - by Ed Guiness

  Suppose I have a list of strings where each string is exactly 4 characters long and unique within the list. For each of these strings I want to identify the position of the characters within the string that make the string unique. So for a list of three strings abcd abcc bbcb For the first string I want to identify the character in 4th position d since d does not appear in the 4th position in any other string. For the second string I want to identify the character in 4th position c. For the third string it I want to identify the character in 1st position b AND the character in 4th position, also b. This could be concisely represented as abcd -> ...d abcc -> ...c bbcb -> b..b If you consider the same problem but with a list of binary numbers 0101 0011 1111 Then the result I want would be 0101 -> ..0. 0011 -> .0.. 1111 -> 1... Staying with the binary theme I can use XOR to identify which bits are unique within two binary numbers since 0101 ^ 0011 = 0110 which I can interpret as meaning that in this case the 2nd and 3rd bits (reading left to right) are unique between these two binary numbers. This technique might be a red herring unless somehow it can be extended to the larger list. A brute-force approach would be to look at each string in turn, and for each string to iterate through vertical slices of the remainder of the strings in the list. So for the list abcd abcc bbcb I would start with abcd and iterate through vertical slices of abcc bbcb where these vertical slices would be a | b | c | c b | b | c | b or in list form, "ab", "bb", "cc", "cb". This would result in four comparisons a : ab -> . (a is not unique) b : bb -> . (b is not unique) c : cc -> . (c is not unique) d : cb -> d (d is unique) or concisely abcd -> ...d Maybe it's wishful thinking, but I have a feeling that there should be an elegant and general solution that would apply to an arbitrarily large list of strings (or binary numbers). But if there is I haven't yet been able to see it. I hope to use this algorithm to to derive minimal signatures from a collection of unique images (bitmaps) in order to efficiently identify those images at a future time. If future efficiency wasn't a concern I would use a simple hash of each image. Can you improve on brute force?

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• TicTacToe AI Making Incorrect Decisions

  - by Chris Douglass

  A little background: as a way to learn multinode trees in C++, I decided to generate all possible TicTacToe boards and store them in a tree such that the branch beginning at a node are all boards that can follow from that node, and the children of a node are boards that follow in one move. After that, I thought it would be fun to write an AI to play TicTacToe using that tree as a decision tree. TTT is a solvable problem where a perfect player will never lose, so it seemed an easy AI to code for my first time trying an AI. Now when I first implemented the AI, I went back and added two fields to each node upon generation: the # of times X will win & the # of times O will win in all children below that node. I figured the best solution was to simply have my AI on each move choose and go down the subtree where it wins the most times. Then I discovered that while it plays perfect most of the time, I found ways where I could beat it. It wasn't a problem with my code, simply a problem with the way I had the AI choose it's path. Then I decided to have it choose the tree with either the maximum wins for the computer or the maximum losses for the human, whichever was more. This made it perform BETTER, but still not perfect. I could still beat it. So I have two ideas and I'm hoping for input on which is better: 1) Instead of maximizing the wins or losses, instead I could assign values of 1 for a win, 0 for a draw, and -1 for a loss. Then choosing the tree with the highest value will be the best move because that next node can't be a move that results in a loss. It's an easy change in the board generation, but it retains the same search space and memory usage. Or... 2) During board generation, if there is a board such that either X or O will win in their next move, only the child that prevents that win will be generated. No other child nodes will be considered, and then generation will proceed as normal after that. It shrinks the size of the tree, but then I have to implement an algorithm to determine if there is a one move win and I think that can only be done in linear time (making board generation a lot slower I think?) Which is better, or is there an even better solution?

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