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• Code Golf: Diamond Pattern

  - by LiraNuna

  The challenge The shortest code by character count to output a a pattern of diamonds according to the input. The input is composed of 3 positive numbers representing the size of the diamond and the size of the grid. A diamond is made from the ASCII characters / and \ with spaces. A diamond of size 1 is: /\ \/ The size of the grid consists from width and height of number of diamonds. Test cases Input: 1 6 2 Output: /\/\/\/\/\/\ \/\/\/\/\/\/ /\/\/\/\/\/\ \/\/\/\/\/\/ Input: 2 2 2 Output: /\ /\ / \/ \ \ /\ / \/ \/ /\ /\ / \/ \ \ /\ / \/ \/ Input 4 1 3 Output: /\ /\ /\ / \ / \ / \ / \ / \ / \ / \/ \/ \ \ /\ /\ / \ / \ / \ / \ / \ / \ / \/ \/ \/ Code count includes input/output (i.e full program).

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• FileReader vs FileInputReader. split vs Pattern

  - by abdeslam

  I'm working with a file with about 2G. I want to read the file line by line to find some specific terms. Whitch class can I better use: FileReader or FileInputStream? And how can I find the specific words efficiently. I'm just using the split() method, but may be can I use the java.util.regex.Pattern class in combination with java.util.regex.Matcher class. So the Questions are: which class can I use: the FileReader or the FileInputStream? can I use the split method or the regex classes Does someone has an answer to this questions? Thans.

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• Regex Pattern for ignoring a custom escape character

  - by user1517464

  I am trying to find a suitable regex for matching pair of custom characters in an input string. These custom characters are replaced by their corresponding html tags. For e.g. The input string can have underscores in pairs to indicate words in bold. Hence, _Name_ outputs as <b>Name</b> However if there is a genuine underscore in the string, it cannot be replaced by "bold" tags and has to be ignored. The genuine underscore has to be preceded by / (I couldn't find a better character, it could be one more underscore or hyphen or whatever). Any single or paired occurrance of this genuine underscore has to be ignored by regex. So far I could come up with this regex: var pattern = @"(?!/)_(.*?)(?!/)_"; But it fails in below input string: _Tom_Katy/_Richard/_/_Stephan_and many users It outputs as <b>Tom</b>Katy/<b>Richard/_/</b>Stephan_and many users Many Thanks in Advance, Pr

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• Best Design pattern for social media file transfer

  - by Onema

  Our system would like our clients to link their accounts with different social media sites like youtube, vimeo, facebook, myspace and so on. One of the benefits we would like to give to the user is to transfer, update and delete files they have uploaded to our sites and transfer them to the social media sites mentioned above. this files could be videos, images or audio. We started thinking about using a strategy pattern, as all of these sites share a common process ( authentication, connection, use the API to transfer/edit/delete the file ), but we soon realized that it may not work as me may want to use some of the extended functionality that is specific to each service (eg: associate a youtube video with a channel, or upload images to a specific album on facebook, and much, much more...) My question is, what would be the best Structural Design Patter to use for this scenario?

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• Factory Method Pattern using Generics-C#

  - by nanda

  Just I am learning Generics.When i have an Abstract Method pattern like : //Abstract Product interface IPage { string pageType(); } //Concerete Product 1 class ResumePage : IPage { public string pageType() { return "Resume Page"; } } //Concrete Product 2 class SummaryPage : IPage { public string pageType() { return "SummaryPage"; } } //Fcatory Creator class FactoryCreator { public IPage CreateOnRequirement(int i) { if (i == 1) return new ResumePage(); else { return new SummaryPage(); } } } //Client/Consumer void Main() { FactoryCreator c = new FactoryCreator(); IPage p; p = c.CreateOnRequirement(1); Console.WriteLine("Page Type is {0}", p.pageType()); p = c.CreateOnRequirement(2); Console.WriteLine("Page Type is {0}", p.pageType()); Console.ReadLine(); } how to convert the code using generics?

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• Java 'Prototype' pattern - new vs clone vs class.newInstance

  - by Guillaume

  In my project there are some 'Prototype' factories that create instances by cloning a final private instance. The author of those factories says that this pattern provides better performance than calling 'new' operator. Using google to get some clues about that, I've found nothing really relevant about that. Here is a small excerpt found in a javdoc from an unknown project javdoc from an unknown project Sadly, clone() is rather slower than calling new. However it is a lot faster than calling java.lang.Class.newInstance(), and somewhat faster than rolling our own "cloner" method. For me it's looking like an old best practice of the java 1.1 time. Does someone know more about this ? Is this a good practice to use that with 'modern' jvm ?

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• Pattern Matching in Scheme

  - by kunjaan

  How do I accept the following input? (list of 0 or more charcters and ends with 3) or (list of 1 or more characters 4 and 0 or more characters after 4) something like (match ( list 3)) -> #t (match ( list 1 2 3)) -> #t (match (list 1 2 3 4)) -> #t (match (list 1 2 3 4 5)) -> #t (match (list 4)) -> #f EDIT: THIS IS NOT MY HOMEWORK. I trying to write something like ELIZA from PAIP but I know only how to write a pattern that begins with a word.

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• How to show that the double-checked-lock pattern with Dictionary's TryGetValue is not threadsafe in

  - by Amir

  Recently I've seen some C# projects that use a double-checked-lock pattern on a Dictionary. Something like this: private static readonly object _lock = new object(); private static volatile IDictionary<string, object> _cache = new Dictionary<string, object>(); public static object Create(string key) { object val; if (!_cache.TryGetValue(key, out val)) { lock (_lock) { if (!_cache.TryGetValue(key, out val)) { val = new object(); // factory construction based on key here. _cache.Add(key, val); } } } return val; } This code is incorrect, since the Dictionary can be "growing" the collection in _cache.Add() while _cache.TryGetValue (outside the lock) is iterating over the collection. It might be extremely unlikely in many situations, but is still wrong. Is there a simple program to demonstrate that this code fails? Does it make sense to incorporate this into a unit test? And if so, how?

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• Which design pattern to manage windows?

  - by Lu Lu

  Hello, I am using .NET 2.0 & C# to develop a WinForm Mdi application. It will have a Main Window and a lot of mdi windows. I am thinking I should use which design pattern to manage mdi windows. Because I want only one instance for each window, if window is existed, I will show it on top, & otherwise I will create and show it. Note: a mdi window is opened from Menus of Main Window or open from another mdi window. An example is very good. Update: Menu's status is depended on mdi window's status. Ex: If Window 'A' is openned - menu 'A' - disabled. When window 'A' is closed - I update menu 'A' status to Enabled. Thanks.

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• Exception in JEE application Email Notification Pattern

  - by Build Monkey

  We have spring 3.0.x based application, we use SimpleMappingExceptionResolver which sends emails on an exception, when the exception happens within the DispatcherServlet. This gives us following flexibility: Subject can include who the logged in user is, so that we can send personalized email to the user Subject also includes the server on which the error occurred The request params, request url, and headers -- helped us find some problems when search engine indexing the site. However, lately we have been finding the exceptions have been occurring in the filters, and since this is not going through the Resolver, we dont get any emails. We dont like the log4j email appender solution, and not writing another filter to send emails seems right. Is there an accepted pattern to resolve this issue

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• problem in basic implementation of MVVM pattern - Services

  - by netmajor

  I watch some video and read articles about MVVM pattern and start thinking how should I implement it in my Silverlight app. So at first I create Silverlight application. I think that for clear view I create 3 folders: View - for each user control page in my app, ViewModel - for c# class which will querying date and Model- Entity Data Model of my SQL Server or Oracle Database. And now I am confused, cause I want to implement *WCF/RIA Services/Web services* in my project. In which folder should I put in class of services? I see in examples that Services take date and filtering it and then output data was binding in View - so It looks as ViewModel. But I was sure that someone use Services in Model and that I want to do. But how? Can someone explain me implementing Services as Model? Is my point of view at MVVM is correctly?

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• Which design pattern should I be using?

  - by Gabriel

  Here's briefly what I'm trying to do. The user supplies me with a link to a photo from one of several photo-sharing websites (such as Flickr, Zooomr, et. al). I then do some processing on the photo using their respective APIs. Right now, I'm only implementing one service, but I will most likely add more in the near future. I don't want to have a bunch of if/else or switch statements to define the logic for the different websites (but maybe that's necessary?) I'd rather just call GetImage(url) and have it get me the image from whatever service the url's domain is from. I'm confused how the GetImage function and classes should be designed. Maybe I need the strategy pattern? I'm still reading and trying to understand the various design patterns and how I could make one fit in this case. I'm doing this in C#, but this question is language-agnostic.

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• Generalized plugable caching pattern?

  - by BCS

  Given that it's one of the hard things in computer science, does anyone know of a way to set up a plugable caching strategy? What I'm thinking of would allow me to write a program with minimal thought as to what needs to be cached (e.i. use some sort of boiler-plate, low/no cost pattern that compiles away to nothing anywhere I might want caching) and then when things are further along and I know where I need caching I can add it in without making invasive code changes. As an idea to the kind of solution I'm looking for; I'm working with the D programing language (but halfway sane C++ would be fine) and I like template.

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• WCF competitive consumer pattern

  - by Simon Thompson

  Is it possible to create a WCF service (web service) that only accepts a single connection at any one time with all other calls either queued or rejected. Need to implement the competitive consumer pattern where there are a number of clients which could deal with task at hand but when a client askes for more work a task must go to only one of them. Usual done as part of an enterprise service bus but can not find one that I'm happy to start using so looking to get this behaviour through a WCF service. Any ideas people ?

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• Pattern filters in Laravel 4

  - by ali A

  I want to make a pattern route, to redirect users to login page when they are not logged in. I searched but couldn't find a solution. as always Laravel's Documentation is useless! I have this in my filter.php Route::filter('auth', function() { if (Auth::guest()) return Redirect::guest('login'); }); Route::filter('auth.basic', function() { return Auth::basic(); }); And this route in my routes.php Route::when('/*', 'auth' ); but It's not working. How can I do that?

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• Design Pattern for Server Emulator

  - by adisembiring

  I wanna build server socket emulator, but I want implement some design pattern there. I will described my case study that I have simplified like these: My Server Socket will always listen client socket. While some request message come from the client socket, the server emulator will response the client through the socket. the response is response code. '00' will describe request message processed successfully, and another response code expect '00' will describe there are some error while processing the message request. IN the server there are some UI, this UI contain check response parameter such as. response code timeout interval While the server want to response the client message, the response code taken from input parameter response form UI check the timeout interval, it will create sleep thread and the interval taken from timeout interval input from UI. I have implement the function, but I create it in one class. I feel it so sucks. Can you suggest me what class / interface that I must create to refactor my code.

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• Server Emulator Design Pattern

  - by adisembiring

  I wanna build server socket emulator, but I want implement some design pattern there. I will described my case study that I have simplified like these: My Server Socket will always listen client socket. While some request message come from the client socket, the server emulator will response the client through the socket. the response is response code. '00' will describe request message processed successfully, and another response code expect '00' will describe there are some error while processing the message request. IN the server there are some UI, this UI contain check response parameter such as. response code timeout interval While the server want to response the client message, the response code taken from input parameter response form UI check the timeout interval, it will create sleep thread and the interval taken from timeout interval input from UI. I have implement the function, but I create it in one class. I feel it so sucks. Can you suggest me what class / interface that I must create to refactor my code.

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• some confusions to singleton pattern in PHP

  - by SpawnCxy

  Hi all, In my team I've been told to write resource class like this style: class MemcacheService { private static $instance = null; private function __construct() { } public static function getInstance($fortest = false) { if (self::$instance == null) { self::$instance = new Memcached(); if ($fortest) { self::$instance->addServer(MEMTEST_HOST, MEMTEST_PORT); } else { self::$instance->addServer(MEM_HOST, MEM_PORT); } } return self::$instance; } } But I think in PHP resource handles will be released and initialized again every time after a request over. That means MemcacheService::getInstance() is totally equal new Memcached() which cannot be called singleton pattern at all. Please correct me if I'm wrong. Regards

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• Search for a pattern in a list of strings - Python

  - by Holtz

  I have a list of strings containing filenames such as, file_names = ['filei.txt','filej.txt','filek.txt','file2i.txt','file2j.txt','file2k.txt','file3i.txt','file3j.txt','file3k.txt'] I then remove the .txt extension using: extension = os.path.commonprefix([n[::-1] for n in file_names])[::-1] file_names_strip = [n[:-len(extension)] for n in file_names] And then return the last character of each string in the list file_names_strip: h = [n[-1:] for n in file_names_strip] Which gives h = ['i', 'j', 'k', 'i', 'j', 'k', 'i', 'j', 'k'] How can i test for a pattern of strings in h? So if i,j,k occur sequentially it would return True and False if not. I need to know this because not all file names are formatted like they are in file_names. So: test_ijk_pattern(h) = True no_pattern = ['1','2','3','1','2','3','1','2','3'] test_ijk_pattern(no_pattern) = False

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• db2 sql pattern matching

  - by Jitesh

  I have a table in db2 which has the following fields int xyz; string myId; string myName; Example dataset xyz | myid | myname -------------------------------- 1 | ABC.123.456 | ABC 2 | PRQS.12.34 | PQRS 3 | ZZZ.3.2.2 | blah I want to extract the rows where myName matches the character upto "." in the myId field. So from the above 3 rows, I want the firs 2 rows since myName is present in myId before "." How can I do this in the query, can I do some kind of pattern matching inside the query?

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• Need help understanding the MVC design pattern

  - by Doron Sinai

  Hi, I am trying to find a ood example of MVC design pattern in java. This is what i understood from reading about it, please correct me if I am wrong: I have the Model part which is the logic behind the program, let's say if we have a phonebook, so adding and removing contact from the Array will be the model. The Gui is the view and it contains buttons that upon clicking them, the model is changing. What I am trying to undersand what is the controller part, is it the ActionListeners? how to you seperate those modules in practice. thank you

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• creational pattern for instances depending on multiple subclass instances

  - by markusw

  I have a problem, for that I was not able to identify a suitable design pattern. I want to create instances depending on a given type that has been passed to a factory method. What I am doing until now is the following: T create(SuperType x) { if (x instanceof SubType1) { // do some stuff and return a new SubType extends T } else if (x instanceof SubType2) { // do some stuff and return a new SubType extends T } else if ... } else { throw new UnSupportedOperationException("nothing defined for " + x); } } It seems not to be best pratice for me. Has anybody an idea how to solve this in a better way?

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• Self-Configuring Classes W/ Command Line Args: Pattern or Anti-Pattern?

  - by dsimcha

  I've got a program where a lot of classes have really complicated configuration requirements. I've adopted the pattern of decentralizing the configuration and allowing each class to take and parse the command line/configuration file arguments in its c'tor and do whatever it needs with them. (These are very coarse-grained classes that are only instantiated a few times, so there is absolutely no performance issue here.) This avoids having to do shotgun surgery to plumb new options I add through all the levels they need to be passed through. It also avoids having to specify each configuration option in multiple places (where it's parsed and where it's used). What are some advantages/disadvantages of this style of programming? It seems to reduce separation of concerns in that every class is now doing configuration stuff, and to make programs less self-documenting because what parameters a class takes becomes less explicit. OTOH, it seems to increase encapsulation in that it makes each class more self-contained because no other part of the program needs to know exactly what configuration parameters a class might need.

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• What software design pattern is best for the following scenario (C#)

  - by askjdh

  I have a gps device that records data e.g. datetime, latitude, longitude I have an sdk that reads the data from the device. The way the data is read: A command packet (basically a combination of int values in a struct) is sent to the device. The device responds with the data in fixed size chunks e.g. 64bytes Depending on the command issued I will get back differect data structs e.g. sending command 1 to the device returns a struct like struct x { id int, name char[20] } command 2 returns a collection of the following structs (basically it boils down to an array of the structs - y[12]) struct y { date datetime, lat decimal, lon decimal } I would then want to convert the struct to a class and save the data to a database. What would be the best way to encapsulate the entire process, preferably using some established design pattern? Many thanks M

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• Dashboard pattern: HorizontalScrollView with pagination or ScrollView?

  - by Macarse

  I am starting a new application and I am willing to use the Dashboard pattern. For example: The Google IO app uses it: My issue is that the amount of buttons will be more than six. I'm not sure if I should use vertical or horizontal scrolling. Vertical scrolling could be done with a ScrollView or a GridView but I am not sure which would be the easier way to implement the horizontal version. I was thinking of using an HorizontalScrollView but it doesn't have pagination. It should feel similar to the tweetdeck app. How would you implement it?

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