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• Enumerating all hamiltonian paths from start to end vertex in grid graph

  - by Eric

  Hello, I'm trying to count the number of Hamiltonian paths from a specified start vertex that end at another specified vertex in a grid graph. Right now I have a solution that uses backtracking recursion but is incredibly slow in practice (e.g. O(n!) / 3 hours for 7x7). I've tried a couple of speedup techniques such as maintaining a list of reachable nodes, making sure the end node is still reachable, and checking for isolated nodes, but all of these slowed my solution down. I know that the problem is NP-complete, but it seems like some reasonable speedups should be achievable in the grid structure. Since I'm trying to count all the paths, I'm sure that the search must be exhaustive, but I'm having trouble figuring out how to prune out paths that aren't promising. Does anyone have some suggestions for speeding the search up? Or an alternate search algorithm?

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• Enums With Default Throw Clause?

  - by Tom Tresansky

  I noticed the following in the Java Language spec in the section on enumerations here: link switch(this) { case PLUS: return x + y; case MINUS: return x - y; case TIMES: return x * y; case DIVIDE: return x / y; } throw new AssertionError("Unknown op: " + this); However, looking at the switch statement definition section, I didn't notice this particular syntax (the associated throw statement) anywhere. Can I use this sort of "default case is throw an exception" syntactic sugar outside of enum definitions? Does it have any special name? Is this considered a good/bad practice for short-cutting this behavior of "anything not in the list throws an exception"?

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• SQL LIKE question

  - by user176121

  I was wondering if there's a drawback (other than bad practice) to using something like this SELECT * FROM my_table WHERE id LIKE '1'; where id is an integer. I know you're supposed to use id=1 but I am writing a java program and if everything can use LIKE it'll be a lot easier for me. Also, so far, everything works fine; I get the correct query results, so if there is no drawback I will continue doing it like this. edit: I am using MySQL.

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• What is the best way to add attributes to auto-generated entities (using VS2010 and EF4)

  - by Dani

  ASP.NET MVC2 has strong support for using attributes on entities (validation, and extending Html helper class and more). If I generated my Model from the Database using VS2010 EF4 Entity Data Model (edmx and it's cs class), And I want to add attributes on some of the entities. what would be the best practice ? how should I cope with updating the model (adding more fields / tables to the database and merging them into the edmx) - will it keep my attributes or generate a new cs file erasing everything ? (Manual changes to this file may cause unexpected behavior in your application.) (Manual changes to this file will be overwritten if the code is regenerated.)

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• How is an SOA architecture really supposed to be implemented?

  - by smaye81

  My project is converting a legacy fat-client desktop application into the web. The database is not changing as a result. Consequently, we are being forced to call external web services to access data in our own database. Couple this with the fact that some parts of our application are allowed to access the database directly through DAOs (a practice that is much faster and easier). The functionality we're supposed to call web services for are what has been deemed necessary for downstream, dependent systems. Is this really how SOA is supposed to work? Admittedly, this is my first foray into the SOA world, but I have to think this is the complete wrong way to go about this.

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• What is the optimal number of threads for performing IO operations in java?

  - by marc

  In Goetz's "Java Concurrency in Practice", in a footnote on page 101, he writes "For computational problems like this that do not I/O and access no shared data, Ncpu or Ncpu+1 threads yield optimal throughput; more threads do not help, and may in fact degrade performance..." My question is, when performing I/O operations such as file writing, file reading, file deleting, etc, are there guidelines for the number of threads to use to achieve maximum performance? I understand this will be just a guide number, since disk speeds and a host of other factors play into this. Still, I'm wondering: can 20 threads write 1000 separate files to disk faster than 4 threads can on a 4-cpu machine?

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• how to handle exceptions/errors in php?

  - by fayer

  when using 3rd part libraries they tend to throw exceptions to the browser and hence kill the script. eg. if im using doctrine and insert a duplicate record to the database it will throw an exception. i wonder, what is best practice for handling these exceptions. should i always do a try...catch? but doesn't that mean that i will have try...catch all over the script and for every single function/class i use? Or is it just for debugging? i don't quite get the picture. Cause if a record already exists in a database, i want to tell the user "Record already exists". And if i code a library or a function, should i always use "throw new Expcetion($message, $code)" when i want to create an error? Please shed a light on how one should create/handle exceptions/errors. Thanks

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• make db connection persistent throught zend framework

  - by kamikaze_pilot

  I'm using zend framework. currently everytime I need to use the db I go ahead and connect to the DB: function connect(){ $connParams = array("host" => $host, "port" => $port, "username" => $username, "password" => $password, "dbname" => $dbname); $db = new Zend_Db_Adapter_Pdo_Mysql($connParams); return $db } so I would just call the connect() function everytime I need to use the db My question is...suppose I want to reuse $db everywhere in my site and only connect once in the very initial stage of the site load and then close the connection right before the site gets sent to the user, what would be the best practice to accomplish this? Which file in Zend should I save $db in, what method should I use to save it (global variable?), and which file should I do the connection closing in?

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• How to synchronize static method in java.

  - by Summer_More_More_Tea

  Hi there: I come up with this question when implementing singleton pattern in Java. Even though the example listed blow is not my real code, yet very similar to the original one. public class ConnectionFactory{ private static ConnectionFactory instance; public static synchronized ConnectionFactory getInstance(){ if( instance == null ){ instance = new ConnectionFactory(); } return instance; } private ConnectionFactory(){ // private constructor implementation } } Because I'm not quite sure about the behavior of a static synchronized method, I get some suggestion from google -- do not have (or as less as possible) multiple static synchronized methods in the same class. I guess when implementing static synchronized method, a lock belongs to Class object is used so that multiple static synchronized methods may degrade performance of the system. Am I right? or JVM use other mechanism to implement static synchronized method? What's the best practice if I have to implement multiple static synchronized methods in a class? Thank you all! Kind regards!

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• Structuremap Configuration with generics

  - by DarthVader

  I have IRepository interface with which i want to use NHibernateRepository. How do i configure it with structure map? protected void ConfigureDependencies() { ObjectFactory.Initialize( x => { x.For<ILogger>().Use<Logger>(); x.For<IRepository<T>>().Use<NHibernateRepository<T>>(); } ); } I m getting an error on T. Another question I have is if it s OK to make an ApplicationContext static class, configure it with structure map and provide instances with it? I have read that static classes are bad, but I dont want to initialize the ApplicationContext class that I have the injections everywhere. What s the best practice for this? Thanks.

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• jQuery - getting the id of the item selected

  - by John Leonard

  I have a basic jQuery selector question. Let's say I'm parsing JSON and generating a row of data for each item in my result set. On each item row, I want an action button. What is the best practice to script that button so its click action can reference the data specific to that row? Starting with the block below, how do I generate a 'Click Me' button that when clicked will alert with its json data? $.getJSON(url,params,function(json){ if(json.items){ $.each(json.items, function(i, n){ var item = json.items[i];

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• How to? - part of the site over ssl, other part not

  - by spirytus

  What is common practice for coding web applications where part of the site has to be secured (e.g. checkout section) and part not necessarily, lets say homepage. As far as I know sharing sessions in between http and https parts of the site is not easily possible (or is it?). What would be common approach if I wanted to display on http page like homepage, shopping cart data (items) that users ordered on https pages? How those two parts of the site would communicate if necessary? Also isn't it security flaw in popular shopping carts as it seems that many of these have only checkout pages secured (ssl) and the rest not? I'm using php if it makes any difference.

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• App stays in splash screen in iOS 7.0.3

  - by Sathish

  Recently in iOS 7.0.3, my app stays in the splash screen and was not going into the app at all. If i kill the app, and launch it again it opens up without any issues. Can anyone help me on this issue?. I think the application -didFinishLaunchingWithOptions was not returning yes. Note: I have a lot of stuffs like deleting database, initializing a dozen of buttons in appdelegate's *init* function. I know that it is a bad practice to have things in init but since its been there for more than 4 years and was working fine with previous OS versions i didn't find a good reason to change it. Also this issue is not happening all the time. My app size is 40 MB. Thanks in advance...

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• Do you use another language instead of english ?

  - by Luc M

  Duplicate Should identifiers and comments be always in English or in the native language of the application and developers? For people who are not native English speakers, which language do you use to declare variables, classes, etc. ? I had to continue a project from a Spanish guy. Everything was written in Spanish. Since this time, I have decided to use English identifiers ( variables, classes, file names) and write comments in french. Everything was in french before that. What are the general recommendations about that practice? Do you use English everywhere knowing that no English people will work on your project ? Edit : Here's a post from Jeff Atwood about this subject: The Ugly American Programmer

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• Better way of enforcing this template?

  - by Dennis Ritchie

  Currently, I have a function template like this that converts a vector into a string (just a natural string, separating the elements with a comma): //the type T must be passable into std::to_string template<typename T> std::string vec_to_str(const std::vector<T> &vec); As you can see, this is only meant for vectors whose elements can be passed into the built-in std::to_string function (such as int, double, etc.) Is it considered a good practice to document with comments the allowed T? If not, what should I do? Is it possible to enforce this in a better way?

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• Haskell: Defaulting constraints to type

  - by yairchu

  Consider this example: applyKTimes :: Integral i => i -> (a -> a) -> a -> a applyKTimes 0 _ x = x applyKTimes k f x = applyKTimes (k-1) f (f x) applyThrice :: (a -> a) -> a -> a applyThrice = applyKTimes 3 The 3 in applyThrice is defaulted by GHC to an Integer as shown when compiling with -Wall: Warning: Defaulting the following constraint(s) to type 'Integer' 'Integral t' arising from a use of 'applyKTimes' So I guess that Integer is the default Integral a => a. Is there a way to define "default types" for other constraints too? Is using default types bad practice? (it does complain when using -Wall..)

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• How can I prevent ADO from creating multiple SPIDs?

  - by stusmith

  I'm working on an application that creates a single ADO connection and keeps it open for the lifetime of the application. I have connection pooling turned off. (Please ignore the fact that this might not be best practice for the purposes of this question). If I spawn a new thread and use the exact same ADO connection, it uses a new SPID behind the scenes. Is there anyway to ensure an ADO connection always uses the same SPID, across all threads? (For reference the application is VC++ using ADO via COM to SQL Server).

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• Why do I need to give my options a value attribute in my dropdown? JQuery.

  - by Alex

  So far in my web developing experiences, I've noticed that almost all web developers/designers choose to give their options in a select a value like so: <select name="foo"> <option value="bar">BarCheese</option> // etc. // etc. </select> Is this because it is best practice to do so? I ask this because I have done a lot of work with jQuery and dropdown's lately, and sometimes I get really annoyed when I have to check something like: $('select[name=foo]').val() == "bar"); To me, many times that seems less clear than just being able to check the val() against BarCheese. So why is it that most web developers/designers specify a value paramater instead of just letting the options actual value be its value?

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• Using scanf() in C++ programs is faster than using cin ?

  - by zeroDivisible

  Hello, I don't know if this is true, but when I was reading FAQ on one of the problem providing sites, I found something, that poke my attention: Check your input/output methods. In C++, using cin and cout is too slow. Use these, and you will guarantee not being able to solve any problem with a decent amount of input or output. Use printf and scanf instead. Can someone please clarify this? Is really using scanf() in C++ programs faster than using cin something ? If yes, that is it a good practice to use it in C++ programs? I thought that it was C specific, though I am just learning C++...

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• VS2005 and VSS. Should .exes, .dlls, pdbs, .resource and generated .xml files go in VSS?

  - by Velika

  It seems like the following type of files need to be writable to be able to compile a solution. .exe .dll .pdb (if debugging) .resource (?) .xml (at least the system generated ones. I'm not sure if they are just all XML documentationf iles) If they were checked in and could only be overwritten by the compiler by the person who had them checked out, then checking them into sourcesafe and requiring a checkout to modify them, which is attemtped by the compiler each time you run, would interfer with other developer's ability to debug and run. What is the best practice? It seems like VSS automatically adds everything.

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• Mixing .NET 3.5 with 4/4.5 assemblies in the same process

  - by lysergic-acid

  Our team builds a .NET 3.5 WinForms based application that we'd like to migrate to the latest .NET version (4.5). Our application uses many "external" components (can be thought of as plugins) that are also currently .NET 3.5 based. I'd like to know what runtime/core libraries are used in case we convert ONLY THE APPLICATION to compile using .NET 4.5? Should this scenario properly work? (loading .NET 3.5 assemblies in a 4.5 process)? * The plugin assemblies are loaded via reflection. How does the CLR runtime handle such a scenario? is this a safe practice?

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• Pattern for database-wrapper in java

  - by Space_C0wb0y

  I am currently writing a java-class that wraps an SQLite database. This class has two ways to be instantiated: Open an existing database. Create a new database. This is what I cam up with: public class SQLiteDatabaseWrapper { public static SQLiteDatabaseWrapper openExisting(File PathToDB) { return new SQLiteDatabaseWrapper(PathToDB); } public static SQLiteDatabaseWrapper createNew(File PathToDB) { CreateAndInitializeNewDatabase(PathToDB); return new SQLiteDatabaseWrapper(PathToDB); } private SQLiteDatabaseWrapper(File PathToDB) { // Open connection and setup wrapper } } Is this the way to go in Java, or is there any other best practice for this situation?

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• Violation of primary key constraint, multiple users

  - by MC.

  Lets say UserA and UserB both have an application open and are working with the same type of data. UserA inserts a record into the table with value 10 (PrimaryKey='A'), UserB does not currently see the value UserA entered and attempts to insert a new value of 20 (PrimaryKey='A'). What I wanted in this situation was a DBConcurrencyException, but instead what I have is a primary key violation. I understand why, but I have no idea how to resolve this. What is a good practice to deal with such a circumstance? I do not want to merge before updating the database because I want an error to inform the user that multiple users updated this data.

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• On Mac OS X, do you use the shipped python or your own?

  - by The MYYN

  On Tiger, I used a custom python installation to evaluate newer versions and I did not have any problems with that*. Now Snow Leopard is a little more up-to-date and by default ships with $ ls /System/Library/Frameworks/Python.framework/Versions/ 2.3 2.5 2.6 @Current What could be considered best practice? Using the python shipped with Mac OS X or a custom compiled version in, say $HOME. Are there any advantages/disadvantages using the one option over the other? My setup was fairly simple so far and looked like this: Custom compiled Python in $HOME and a $PATH that would look into $HOME/bin first, and subsequently would use my private Python version. Also $PYTHONPATH pointed to this local installation. This way, I did not need to sudo–install packages - virtualenv took care of the rest.

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• Best ways to reuse Java methods

  - by carillonator

  I'm learning Java and OOP, and have been doing the problems at Project Euler for practice (awesome site btw). I find myself doing many of the same things over and over, like: checking if an integer is prime/generating primes generating the Fibonacci series checking if a number is a palindrome What is the best way to store and call these methods? Should I write a utility class and then import it? If so, do I import a .class file or the .java source? I'm working from a plain text editor and the Mac terminal. Thanks!

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