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• Who owes who money optimisation problem

  - by Francis

  Say you have n people, each who owe each other money. In general it should be possible to reduce the amount of transactions that need to take place. i.e. if X owes Y £4 and Y owes X £8, then Y only needs to pay X £4 (1 transaction instead of 2). This becomes harder when X owes Y, but Y owes Z who owes X as well. I can see that you can easily calculate one particular cycle. It helps for me when I think of it as a fully connected graph, with the nodes being the amount each person owes. Problem seems to be NP-complete, but what kind of optimisation algorithm could I make, nevertheless, to reduce the total amount of transactions? Doesn't have to be that efficient, as N is quite small for me.

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• PHP cURL: get headers only from post

  - by Stewart

  There ought to be a way of sending a post request and getting back just the headers. $ch = curl_init('http://www.stackoverflow.com/'); curl_setopt($ch, CURLOPT_HEADER, true); curl_setopt($ch, CURLOPT_POST, true); curl_setopt($ch, CURLOPT_NOBODY, true); doesn't work, because all setting CURLOPT_NOBODY does is to change the request method to HEAD, thereby overriding CURLOPT_POST. I could just leave the last of these lines out and only process the headers, but is there a more efficient way? It's also odd that there doesn't seem to be a way in cURL to truncate the received content to a specified length as there is with file_get_contents.

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• Find all numbers that appear in each of a set of lists

  - by Ankur

  I have several ArrayLists of Integer objects, stored in a HashMap. I want to get a list (ArrayList) of all the numbers (Integer objects) that appear in each list. My thinking so far is: Iterate through each ArrayList and put all the values into a HashSet This will give us a "listing" of all the values in the lists, but only once Iterate through the HashSet 2.1 With each iteration perform ArrayList.contains() 2.2 If none of the ArrayLists return false for the operation add the number to a "master list" which contains all the final values. If you can come up with something faster or more efficient, funny thing is as I wrote this I came up with a reasonably good solution. But I'll still post it just in case it is useful for someone else. But of course if you have a better way please do let me know.

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• Actionscript 3.0 Get all instances of a class?

  - by Windbrand

  I got a ton of movieclips in a class. Is there a more efficient way to apply a function to every instance in the class other than this? var textArray:Array = [ interludes.interludeIntro.interludeBegin1, interludes.interludeIntro.interludeBegin2, interludes.interludeIntro.interludeBegin3, interludes.interludeIntro.interludeBegin4, interludes.interludeIntro.interludeBegin5, interludes.interludeIntro.interludeBegin6, interludes.interludeIntro.interludeBegin7, //... ... ... interludes.interludeIntro.interludeBegin15 ]; for each (var interludeText:MovieClip in interludeBeginText) { interludeText.alpha = 0 //clear all text first } Also for some reason this doesn't work: interludes.interludeIntro.alpha = 0; It permanently turns that class invisible, even if I try to make specific instances visible later with: interludes.interludeIntro.interludeBegin1.alpha = 1; I have NO idea why the above doesn't work. I want to turn every single instance in the class interludeIntro invisible, but I want to turn specific instances visible later. (btw I have no idea how to insert code on this website, pressing "code" doesn't do anything, so pardon the bad formatting)

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• execute javascsript for loop alternately forward and backward

  - by Stiff Mittens

  What I'm trying to do is iterate through an array in chunks, alternating the direction of iteration from chunk to chunk. Confused? So am I. For example, if I want to loop thru an array with 25 elements, but I want to do it in this order: 0, 1, 2, 3, 4, 9, 8, 7, 6, 5, 10, 11, 12, 13, 14, 19, 18, 17, 16, 15, 20, 21, 22, 23, 24, what would be the most efficient way of doing this? I'm looking for something scalable because the array I'm working with now is actually 225 elements and I want to traverse it in 15 element chunks, but that may change at some point. So far, the only method I've figured out that actually works is to hard-wire the iteration order into a second array and then iterate through that in the normal way to get the indices for the original array. But that sucks. Any help would be greatly appreciated.

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• Is this the best way to get the size of a Paper via CUPS?

  - by Lawrence Johnston

  I've got a CUPS job control file. I need to get the actual dimensions of the print that was made. This is the way I've figure out to do it: Get the paper name using the media attribute. (e.g. Letter) Get the printer uri from the printer-uri attribute. (e.g. ipp://localhost/printers/MyPrinter) Get the printer name by passing the printer uri to the IPP_GET_PRINTER_ATTRIBUTES operation and getting the printer-name attribute. (e.g. MyPrinter) Get the path to the PPD passing the printer name to the the cupsGetPPD method. Open the PPD passing the path to the PPD to the ppdOpenFile method. Get the paper size by passing the PPD and paper name to the ppdPageSize method. This will work, but it seems a bit roundabout. Is there a more efficient way of getting what I need?

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• group by country with ActiveRecords in Rails

  - by Adnan

  Hello, I have a table with users: name | country | .. | UK | .. | US | .. | US | .. | UK | .. | FR | .. | FR | .. | UK | .. | UK | .. | DE | .. | DE | .. | UK | .. | CA | . . What is the most efficient way with ActiveRecords to get the list of countries in my view and for each country how many users are from, so: US 123 UK 54 DE 33 . . .

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• linq to sql update data

  - by pranay

  can i update my employee record as given in below function or i have to make query of employee collection first and than i update data public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); db.App3_EMPLOYEEs.Attach(employee); db.SubmitChanges(); return employee.PKEY; } or i have to do this public int updateEmployee(App3_EMPLOYEE employee) { DBContextDataContext db = new DBContextDataContext(); App3_EMPLOYEE emp = db.App3_EMPLOYEEs.Single(e => e.PKEY == employee.PKEY); db.App3_EMPLOYEEs.Attach(employee,emp); db.SubmitChanges(); return employee.PKEY; } But i dont want to use second option is there any efficient way to update data

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• Updating a database periodically with Java

  - by MSR

  I would like to perform updates to a MySQL database using two separate classes (that do different things) -- one doing so every 10 seconds, and the second every minute. I have a few gaps in my Java knowledge and I'm wondering what the best way to achieve it is. Importantly, if connectivity to the database is lost, I need reconnection attempts to occur indefinitely, and I'm guessing the use of Prepared Statements will make queries more efficient. Should the connection to the database be left open all the time or closed between the updates being run? Maybe I also need to think about clearing objects/resources out of memory if the class instances are going to be run indefinitely.

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• Correct way to take absolute value of INT_MIN

  - by aka.nice

  I want to perform some arithmetic in unsigned, and need to take absolute value of negative int, something like do_some_arithmetic_in_unsigned_mode(int some_signed_value) { unsigned int magnitude; int negative; if(some_signed_value<0) { magnitude = 0 - some_signed_value; negative = 1; } else { magnitude = some_signed_value; negative = 0; } ...snip... } But INT_MIN might be problematic, 0 - INT_MIN is UB if performed in signed arithmetic. What is a standard/robust/safe/efficient way to do this in C?

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• Q about AbstractApplicationContext.getBeansOfType() and getBean()

  - by Paul Reiners

  We have the following legacy 2.0.7 Spring code: final Map<String, MyClass> secondaryFactories = (Map<String, MyClass>) context.getBeansOfType(MyClass.class, false, true); return (MyClass) context.getBean("myClass"); where context is an instance of org.springframework.context.support.AbstractApplicationContext Note that we ignore the return value of getBeansOfType(). This works just fine, but the problem is that the call to getBeansOfType() is time-consuming. However, even though we ignore the return value of this call, if we try to eliminate this call, then the instance of MyClass returned by getBean() is not fully initialized. (So, apparently, the call to getBeansOfType() is having some sort of side-effects that we need.) We suspect that the call to getBeansOfType() is overkill and we could do something more lightweight so that the instance of MyClass obtained by the call to getBean() would be fully initialized (but it's not null and no exception is thrown). So, is there a more efficient way of doing this?

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• To use an api or store a large dataset in a rails app?

  - by Dave

  Hi all- I am working on a site that has the potential to need a LOT of space. Basically we hope to have every video game every created stored in a database along with an image of the cover. There are some api's out there that might be able to help, like GiantBomb's (www.giantbomb.com). We are trying to decide whether to store the data locally and if so where to find that comprehensive a list, or make calls to the api on demand. The problem with the latter is likely latency and also downtime problems. Assuming we want to store it locally here are the questions: 1) Where can we find this kind of data (yes, I looked on google, and no I couldnt find anything:)) 2) What is the most efficient way to encode and store the images? Thanks!

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• Accessing two sides of a user-user relationship in rails

  - by Lowgain

  Basically, I have a users model in my rails app, and a fanship model, to facilitate the ability for users to become 'fans' of each other. In my user model, I have: has_many :fanships has_many :fanofs, :through => :fanships In my fanship model, I have: belongs_to :user belongs_to :fanof, :class_name => "User", :foreign_key => "fanof_id" My fanship table basically consists of :id, :user_id and :fanof_id. This all works fine, and I can see what users a specific user is a fan of like: <% @user.fanofs.each do |fan| %> #things <% end %> My question is, how can I get a list of the users that are a fan of this specific user? I'd like it if I could just have something like @user.fans, but if that isn't possible what is the most efficient way of going about this? Thanks!

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• Generic Database table design

  - by Gazeth

  Just trying to figure out the best way to design my table for the following scenario: I have several areas in my system (documents, projects, groups and clients) and each of these can have comments logged against them. My question is should I have one table like this: CommentID DocumentID ProjectID GroupID ClientID etc Where only one of the ids will have data and the rest will be NULL or should I have a seperate CommentType table and have my comments table like this: CommentID CommentTypeID ResourceID (this being the id of the project/doc/client) etc My thoughts are that option 2 would be more efficient from an indexing point of view?

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• delete all records except the id I have in a python list

  - by jay_t

  Hi all, I want to delete all records in a mysql db except the record id's I have in a list. The length of that list can vary and could easily contain 2000+ id's, ... Currently I convert my list to a string so it fits in something like this: cursor.execute("""delete from table where id not in (%s)""",(list)) Which doesn't feel right and I have no idea how long list is allowed to be, .... What's the most efficient way of doing this from python? Altering the structure of table with an extra field to mark/unmark records for deletion would be great but not an option. Having a dedicated table storing the id's would indeed be helpful then this can just be done through a sql query... but I would really like to avoid these options if possible. Thanks,

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• Most optimal way to detect if black (or any color pixels) exist in an image file?

  - by Zando

  What's the best and most flexible algorithm to detect any black (or colored pixel) in a given image file? Say I'm given an image file that could, say, have a blue background. And any non blue pixel, including a white pixel, is counted as a "mark". The function returns true if there are X number of pixels that deviate from each other at a certain threshold. I thought it'd be fastest to just simply iterate through every pixel and see if its color matches the last. But if it's the case that pixel (0,0) is deviant, and every other pixel is the same color (and I want to allow at least a couple deviated pixels before considering an image to be "marked), this won't work or be terribly efficient.

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• How to correctly migrate urls from custom asp.net solution to Wordpress?

  - by Marek

  I have a web site built using asp.net with ugly URLs like /DisplayContent.aspx?id=789564. I know how to migrate the database, but the Wordpress urls will be (naturally) different. Can I simply write some mapping or do I have to include a rewrite rule for each subpage (300 pages) in .htaccess? Should I provide a rewrite rule for each existing page that would transform a full old url to the known new url, like for example: /DisplayContent.aspx?id=789798 -> /2010-5-10/Title-Of-The-Post Even if I manage to migrate the URLs, the structure of the HTML for the new content will naturally be different. How does this affect SEO? Should I run asp.net and wordpress side by side and issue the redirects from the asp.net application? What is the most efficient solution to this kind of migration of URLs without doing PHP programming?

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• hunting maven dependencies

  - by Tom

  I want to start using maven in code I distribute but I can't find an efficient way to work with dependencies. Every new dependency takes me far too long to add. As a simple example, I need to add Tomcat for compilation. Do I really have to manually trawl the repo in my browser to find the group-id, artifact-id and version number? In every case it seems easier to find the non-maven downloads. I hope I've missed something obvious.

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• resource for migrating from C/C++ to C#

  - by EquinoX

  I know there's a lot of resource for this via google, but I just wanted to hear personally from people who have experienced this before. I've programmed in C for 3 years and C++ for a year and now I am moving to C#. I know this is not going to be a so hard transition but could you guys that had this same experience with me share resources on a good book, article, or blog to make my study experience more efficient. Any tips/tricks or gotchas when moving to C#? Here's one article that I can find via google. Looking for more goodies from experienced developers here.

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• How to implement a set ?

  - by nomemory

  I want to implement a Set in C. Is it OK to use a linked list, when creating the SET, or should I use another approach ? How do you usually implement your own set (if needed). NOTE: If I use the Linked List approach, I will probably have the following complexities for my operations: init : O(1); destroy: O(n); insert: O(n); remove: O(n); union: O(n*m); intersection: O(n*m); difference: O(n*m); ismember: O(n); issubset: O(n*m); setisequal: O(n*m); O(n*m) seems may be a little to big especially for huge data... Is there a way to implement my Set more efficient ?

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• enumerate all combinations in c++

  - by BCS

  My question is similar to this combinations question but in my case I have N (N 4) small sets (1-2 items per set for now might go to 3 maybe 4) and want to generate each combination of one item from each set. The current solution looks somethinging along the lines of this for(T:: iterator a = setA.begin(); a != setA.end(); ++a) for(T:: iterator b = setB.begin(); b != setB.end(); ++b) for(T:: iterator c = setC.begin(); c != setC.end(); ++c) for(T:: iterator d = setD.begin(); d != setD.end(); ++d) for(T:: iterator e = setE.begin(); e != setE.end(); ++e) something(*a,*b,*c,*d,*e); Simple, effective, probably reasonably efficient, but ugly and not very extensible. Does anyone know of a better/cleaner way to do this?

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• Need advice on cron job'ing a very large process

  - by Arms

  I have a PHP script that grabs data from an external service and saves data to my database. I need this script to run once every minute for every user in the system (of which I expect to be thousands). My question is, what's the most efficient way to run this per user, per minute? At first I thought I would have a function that grabs all the user Ids from my database, iterate over the ids and perform the task for each one, but I think that as the number of users grow, this will take longer, and no longer fall within 1 minute intervals. Perhaps I should queue the user Ids, and perform the task individually for each one? In which case, I'm actually unsure of how to proceed. Thanks in advance for any advice.

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• Iterate over the lines of a string

  - by Space_C0wb0y

  I have a multi-line string defined like this: foo = """ this is a multi-line string. """ I need an iterator that iterates over the individual lines of that string. I could of course do it like this: lineiterator = iter(foo.splitlines()) Is there a more direct way of doing this? In this scenario the string has to traversed once for the splitting, and then again by the parser. It doesn't matter in my test-case, since the string is very short there, I am just asking out of curiosity. Python has so many useful and efficient built-ins for such stuff, but I could find nothing that suits this need.

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• Conditional Branching Issues

  - by Zack

  Here is the code: def main_menu print_main_menu user_selected = gets.chomp if user_selected.downcase == "no" main_menu elsif user_selected == "1" || "2" || "3" || "4" || "5" || "6" || "7" user_selected = user_selected.to_i call_option(user_selected) else main_menu end end This code uses calls to allow a user to make a selection from a main menu. Depending on the input, be it a certain number, a certain word, or something else, the respective method is called (in the case of a valid input) or the main menu is printed again (in the case of an invalid input or "no"). My questions are twofold. 1) Is there an efficient way to get rid of the literal string error that appears as a result of this redundant or statement on the elsif line? (the code itself works fine, but this error appears and is frustrating). 2) When an alternate/unspecified input is made by the user, the else branch doesn't execute and main_method doesn't start over. I have no idea why this is happening. Is there something I'm missing here? Thanks

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• HTML5 - Creating a canvas on top of an SVG(or other image)

  - by cawd

  The reason for asking this question is because I want to be able to draw an arrow between two svg images. I want to use canvas to create the arrows, so firstly I generate the svgs then place a canvas on top of them to be able to draw the arrows. I've tried using style=... but haven't had any luck as everytime I add the canvas element it just pushes my svg images to another pl If there's no easy way to do this I'll just create arrows using SVG, I figured it would be more efficient to use canvas if I had to do lots of arrows in a short amount of time.

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