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• Determining the order of a list of numbers (possibly without sorting)

  - by Victor Liu

  I have an array of unique integers (e.g. val[i]), in arbitrary order, and I would like to populate another array (ord[i]) with the the sorted indexes of the integers. In other words, val[ord[i]] is in sorted order for increasing i. Right now, I just fill in ord with 0, ..., N, then sort it based on the value array, but I am wondering if we can be more efficient about it since ord is not populated to begin with. This is more of a question out of curiousity; I don't really care about the extra overhead from having to prepopulate a list and then sort it (it's small, I use insertion sort). This may be a silly question with an obvious answer, but I couldn't find anything online.

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• Java escape HTML - string replace slow?

  - by cpf

  Hi StackOverflow, I have a Java application that makes heavy use of a large file, to read, process and give through to SolrEmbeddedServer (http://lucene.apache.org/solr/). One of the functions does basic HTML escaping: private String htmlEscape(String input) { return input.replace("&", "&amp;").replace(">", "&gt;").replace("<", "&lt;") .replace("'", "&apos;").replaceAll("\"", "&quot;"); } While profiling the application, the program spends roughly 58% of the time in this function, a total of 47% in replace, and 11% in replaceAll. Now, is the Java replace that slow, or am I on the right path and should I consider the program efficient enough to have its bottleneck in Java and not in my code? (Or am I replacing wrong?) Thanks in advance!

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• Why it is necessary to put comments on check-ins? [closed]

  - by Mik Kardash

  In fact, I always have something to put in when I perform a check-in of my code. However, the question I have is - Is it really so necessary? Does it help so much? How? From one point of view, comments can help you to keep track of changes performed with every check-in. Thus, I will be able to analyze the changes and identify a hypothetic problem a little bit quicker. On the other hand, it takes some time to write useful information into check-in. Is it worth it? What are the pros and cons of writing comments to every check-in? Is there any way to write "efficient" check-in comments?

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• Efficiently using position to control actions

  - by John Ashmore

  I want to use position (returned from a gridview for e.g.) or a similar numeric integer to do various things, e.g. create a sprite, or in any command that wants something other than a number, e.g. I want to use something like: sprites.add(createSprite(R.drawable.image(position)); , where createSprite creates a sprite using the image supplied, instead of: if (position == 1) {sprites.add(createSprite(R.drawable.image1);} if (position == 2) {sprites.add(createSprite(R.drawable.image2);} ...etc There is an easy solution for strings: Most efficient method to use position to open a .java but what about for situations like this one?

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• Efficiently remove points with same slope

  - by Ram

  Hi, In one of mine applications I am dealing with graphics objects. I am using open source GPC library to clip/merge two shapes. To improve accuracy I am sampling (adding multiple points between two edges) existing shapes. But before displaying back the merged shape I need to remove all the points between two edges. But I am not able to find an efficient algorithm that will remove all points between two edges which has same slope with minimum CPU utilization. Currently all points are of type PointF Any pointer on this will be a great help.

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• How can I implement "real time" messaging on Google AppEngine?

  - by Freed

  I'm creating a web application on Google AppEngine where I want the user to be notified a quickly as possible after certain events occour. The problem is similar to say a chat server in that I need something happening on one connection (someone is writing a message in a chat room) to propagate to a number of other connections (other people in that chat room gets the message). To get speedy updates from the server to the client I'm planning on using long polling with XmlHttpRequest, hoping that AppEngine won't interfere other than possibly restriing the timeout. The real problem however is efficient notification between connections on AppEngine. Is there any support for this type of cross connection notification on AppEngine that does not involve busy-waiting? The only tools I can think of to do this at all is either using the data storage (slow) or memcache (unreliable), and none of them would let me avoid busy-waiting. Note: I know about XMPP support on AppEngine. It's related, but I want a browser based solution, sending messages to the users by XMPP is not an option.

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• RegEx to Reject Unescaped Character

  - by JDV72

  I want to restrict usage of unescaped ampersands in a particular input field. I'm having trouble getting a RegEx to kill usage of "&" unless followed by "amp;"...or perhaps just restrict usage of "& " (note the space). I tried to adapt the answer in this thread, but to no avail. Thanks. (FWIW, here's a RegEx I made to ensure that a filename field didn't contain restrited chars. and ended in .mp3. It works fine, but does it look efficient?)

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• Sliding & Fading controls on a C# form

  - by Tommy

  Hey there, I'm trying to implement a way to slide&fade controls around (more than one at the same time possibly) elegantly. So in other words, say i had a picture in the top left corner, and a texbox in the bottom right corner, i'd like to be able to have them slide. not just snap. slide, to the opposite corners and replace eachothers position. Ive been working for awhile but have not come up with anything efficient, even just some of the basic math calculations would be a great start.

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• What technology to use for a RIA

  - by user297159

  I have to develop a online business software solution (similar to ERP) for a company to manage the information exchange for internal use and with external partners. It should be online. What technology should I use, I have checked framewroks like: Flex, Silverlight, Google/GWT, sencha (ExtJS), jQuery, DoJo, Telereik, Infrajistics and others similar. But they seam to be very low level programming. May be this is advantage for other projects, where you need more flexibility, but this project is stright forward. I need something more focused on business software (tables, forms, processes) where and eventually more efficient with less coding, or something I can save time. Is force.com an option? But I can not install this on the customer's servers... Do you have any ideas for me for a web based framework focused on business applications?

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• Is select() Ok to implement single socket read/write timeout ?

  - by chmike

  I have an application processing network communication with blocking calls. Each thread manages a single connection. I've added a timeout on the read and write operation by using select prior to read or write on the socket. Select is known to be inefficient when dealing with large number of sockets. But is it ok, in term of performance to use it with a single socket or are there more efficient methods to add timeout support on single sockets calls ? The benefit of select is to be portable.

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• How do I create a point system in a Rails/Twitter app that assigns points to users and non-authentic

  - by codyvbrown

  I'm building a question and answer application on top of twitter and I'm hitting some snags because I'm inevitably dealing with two classes of users: authenticated and non-authenticated. The site enable users to give points to other users, who may or may not be authenticated, and I want to create a site-wide point system where the application stores and displays this information on their profile. I want to save this point data to the user because that would be faster and more efficient but non-authenticated users aren't in our system, we only have the twitter handle. So instead we display the points in our system like this: @points = point.all( :select => "tag, count(*) AS count", # Return tag and count :group => 'tag', # Group by the tag :order => "2 desc", :conditions => {:twitter_handle => params[:username]}) Is there a better way to do this? Is there a better way to associate data with non-authenticated users?

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• Effective way of String splitting

  - by openidsujoy

  I have a completed string like this N:Pay in Cash++RGI:40++R:200++T:Purchase++IP:N++IS:N++PD:PC++UCP:598.80++UPP:0.00++TCP:598.80++TPP:0.00++QE:1++QS:1++CPC:USD++PPC:Points++D:Y++E:Y++IFE:Y++AD:Y++IR:++MV:++CP:~ ~N:ERedemption++RGI:42++R:200++T:Purchase++IP:N++IS:N++PD:PC++UCP:598.80++UPP:0.00++TCP:598.80++TPP:0.00++QE:1++QS:1++CPC:USD++PPC:Points++D:Y++E:Y++IFE:Y++AD:Y++IR:++MV:++CP: this string is like this It's list of PO's(Payment Options) which are separated by ~~ this list may contains one or more PO contains only Key-Value Pairs which separated by : spaces are denoted by ++ I need to extract the values for Key "RGI" and "N". I can do it via for loop , I want a efficient way to do this. any help on this.

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• sharpziplib - can you add a file without it copying the entire zip first?

  - by schmoopy

  Im trying to add an existing file to a .zip file using sharpziplib - problem is, the zip file is 1GB in size. When i try to add 1 small file (400k) sharpziplib creates a copy/temp of the orig zip file before adding the new file - this poses a problem when the amount of free disk space is less than 2x the zip file you are trying to update. for example: 1GB zip myfile.zip 1GB zip myfile.zip.tmp.293 ZipFile zf = new ZipFile(path); zf.BeginUpdate(); zf.Add(file); // Adding a 400k file here causes a 1GB temp file to be created zf.EndUpdate(); zf.Close(); Is there a more efficient way to do this? Thanks :-)

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• How can I speed up line by line reading of an ASCII file? (C++)

  - by Jon

  Here's a bit of code that is a considerable bottleneck after doing some measuring: //----------------------------------------------------------------------------- // Construct dictionary hash set from dictionary file //----------------------------------------------------------------------------- void constructDictionary(unordered_set<string> &dict) { ifstream wordListFile; wordListFile.open("dictionary.txt"); string word; while( wordListFile >> word ) { if( !word.empty() ) { dict.insert(word); } } wordListFile.close(); } I'm reading in ~200,000 words and this takes about 240 ms on my machine. Is the use of ifstream here efficient? Can I do better? I'm reading about mmap() implementations but I'm not understanding them 100%. The input file is simply text strings with *nix line terminations.

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• When to use Hibernate?

  - by Ramo

  Hi All, I was asked in an interview this question so I answered with the following: -Better Performance: - Efficient queries. - 1st and 2nd level caching. - Good caching gives better scalability. - Good Database Portability: - Changing the DB is as easy as changing the dialect configuration. - Increased Developer Productivity: - Think only in object terms not in query language terms. But I also feel that systems fall in one of the below categories, and Hibernate may not be suited for all these cases, I'm interested in your thoughts about this, do you agree with me? please let me know when would use HB in the following case and why. Write Only Systems: Read Only Systems: Write Mostly Systems: Read Mostly Systems: Regards Ramo

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• Finding mySQL duplicates, then merging data

  - by Michael Pasqualone

  I have a mySQL database with a tad under 2 million rows. The database is non-interactive, so efficiency isn't key. The (simplified) structure I have is: `id` int(11) NOT NULL auto_increment `category` varchar(64) NOT NULL `productListing` varchar(256) NOT NULL Now the problem I would like to solve is, I want to find duplicates on productListing field, merge the data on the category field into a single result - deleting the duplicates. So given the following data: +----+-----------+---------------------------+ | id | category | productListing | +----+-----------+---------------------------+ | 1 | Category1 | productGroup1 | | 2 | Category2 | productGroup1 | | 3 | Category3 | anotherGroup9 | +----+-----------+---------------------------+ What I want to end up is with: +----+----------------------+---------------------------+ | id | category | productListing | +----+----------------------+---------------------------+ | 1 | Category1,Category2 | productGroup1 | | 3 | Category3 | anotherGroup9 | +----+----------------------+---------------------------+ What's the most efficient way to do this either in pure mySQL query or php?

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• Help with MySQL database structure - user notification system

  - by Simon

  Hi, I'd like to send global notifications to my users (1000+ users) and allow them to close the notification box once they have read the message. Basically I may send one notification per week globally ie/ each user get the same message and they are not personal in nature. What is the best way to achieve this? Create 2 tables: **tb_messages** message_id massage_title message_content **tb_read_messages** user_id message_id is-read That way i can just show each user the current notifications that are not read? select * from tb_read_messages WHERE user_id = $user_id AND is-read = no OR is there a more efficient way? Thanks!!!

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• Best place to store large amounts of session data

  - by audiopleb

  I'm building an application that needs to store and re-use large amounts of data per session. So for example, the user selects a large list of list items (say 2000 or significantly more) which have a numeric value as their key then they save that selection and go off to another page, do something else and then come back to the original page and need to load their selections into that page. What is the quickest and most efficient way of storing and reusing that data? In a text file saved with the session id? In a temp db table? In the session data itself (db sessions so size isn't a limit) using a serialised string or using gzcompress or gzencode? Any advice or insight would be great! Thank you!!!!

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• Joining two tables (through a link), one which may yield multiple rows, together into one result.

  - by Eikern

  Lets say I've got a table listing car brands or models: Cars: Id | Brand ----------- 1 | BMW 2 | Audi 3 | Volvo And I've also got another table which links features. Link: Id | carid | featureid ----------------------- 1 | 1 | 1 2 | 1 | 2 3 | 2 | 2 4 | 3 | 1 5 | 3 | 2 6 | 3 | 3 And I've got the table listing the features. Features: Id | Feature ----------- 1 | A/C 2 | 4WD 3 | Heated seats I want to list these results on my front page like this: BMW A/C 4WD Audi 4WD Volvo A/C 4WD Heated seats What's the best/most efficient way of doing this (using PHP and MySQL)?

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• Injecting a dependancy into a base class

  - by Jamie Dixon

  Hey everyone, I'm on a roll today with questions. I'm starting out with Dependency Injection and am having some trouble injecting a dependency into a base class. I have a BaseController controller which my other controllers inherit from. Inside of this base controller I do a number of checks such as determining if the user has the right privileges to view the current page, checking for the existence of some session variables etc. I have a dependency inside of this base controller that I'd like to inject using Ninject however when I set this up as I would for my other dependencies I'm told by the compiler that: Error 1 'MyProject.Controllers.BaseController' does not contain a constructor that takes 0 argument This makes sense but I'm just not sure how to inject this dependency. Should I be using this pattern of using a base controller at all or should I be doing this in a more efficient/correct way?

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• Function chaining depending on boolean result

  - by Markive

  This is just an efficiency question really.. I'm interested to know if there is a more efficient or logical way that people use to handle this sort of scenario. In my asp.net application I am running a script to generate a new project my code at the top level looks like this: Dim ok As Boolean = True ok = createFolderStructure() If ok Then ok = createMDB() If ok Then ok = createProjectConfig() If ok Then ok = updateCompanyConfig() I create a boolean and each function returns a boolean result, the next function in this chain will only run if the previous one was successful. I do this because an asp.net application will continue to run through the page life cycle unless there is an unhandled exception and I don't want my whole application to be screwed up if something in the chain goes wrong (there is a lot of copying and deleting of files etc.. in this example). I was just wondering how other people handle this scenario? the vb.net single line if statement is quite succinct but I'm wondering if there is a better way?

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• How to hash and check for equality of objects with circular references

  - by mfya

  I have a cyclic graph-like structure that is represented by Node objects. A Node is either a scalar value (leaf) or a list of n=1 Nodes (inner node). Because of the possible circular references, I cannot simply use a recursive HashCode() function, that combines the HashCode() of all child nodes: It would end up in an infinite recursion. While the HashCode() part seems at least to be doable by flagging and ignoring already visited nodes, I'm having some troubles to think of a working and efficient algorithm for Equals(). To my surprise I did not find any useful information about this, but I'm sure many smart people have thought about good ways to solve these problems...right? Example (python): A = [ 1, 2, None ]; A[2] = A B = [ 1, 2, None ]; B[2] = B A is equal to B, because it represents exactly the same graph. BTW. This question is not targeted to any specific language, but implementing hashCode() and equals() for the described Node object in Java would be a good practical example.

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• What is the best way to find the digit at n position in a decimal number?

  - by Elijah

  Background I'm working on a symmetric rounding class and I find that I'm stuck with regards to how to best find the number at position x that I will be rounding. I'm sure there is an efficient mathematical way to find the single digit and return it without having to resort to string parsing. Problem Suppose, I have the following (C#) psuedo-code: var position = 3; var value = 102.43587m; // I want this no ? (that is 5) protected static int FindNDigit(decimal value, int position) { // This snippet is what I am searching for } Also, it is worth noting that if my value is a whole number, I will need to return a zero for the result of FindNDigit. Does anyone have any hints on how I should approach this problem? Is this something that is blaringly obvious that I'm missing?

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• Enumerating combinations in a distributed manner

  - by Reyzooti

  I have a problem where I must analyse 500C5 combinations (255244687600) of something. Distributing it over a 10 node cluster where each cluster processes roughly 10^6 combinations per second means the job will be complete in about 7hours. The problem I have is distributing the 255244687600 combinations over the 10 nodes. I'd like to present each node with 25524468760, however the algorithms I'm using can only produce the combinations sequentially, I'd like to be able to pass the set of elements and a range of combination indicies eg: [0-10^7) or [10^7,2.0 10^7) etc and have the nodes themselves figure out the combinations. The algorithms I'm using at the moment are from the following: http://home.roadrunner.com/~hinnant/combinations.html A logical question I've considered using a master node, that enumerates each of the combinations and sends work to each of the nodes, however the overhead incurred in iterating the combinations from a single node and communicating back and forth work is enormous, and will subsequently lead to the master node becoming the bottleneck. Are there any good combination iterating algorithms geared up for efficient/optimal distributed enumeration?

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• Algorithm Question.. Linked List..

  - by AGeek

  Hi, Scenario is as follows:- I want to reverse the direction of the singly linked list, In other words, after the reversal all pointers should now point backwards.. Well the algorithm should take linear time. The solution that i have thought of using another datastructure A Stack.. With the help of which the singly linked list would be easily reversed, with all pointers pointing backwards.. But i am in doubt, that whether the following implementation yeild linear time complexity.. Please comment on this.. And if any other efficient algorithm is in place, then please discuss.. Thanks.

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