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• [WM6] Owner of a component. What exactly is this for?

  - by kornelijepetak

  I am developing an app for Windows Mobile 6 and there is a CameraCaptureDialog class that enables me to call a camera app from my own application. The class has an Owner property that most examples on the internet set to "this". cam.Owner = this; What exactly does this do? I've seen a similar scenario with Windows Forms components/controls by setting the Parent control. In that case I guess it's used only for layout algorithms, but other than that, is there any useful purpose? I don't see how setting an owner of the CameraCaptureDialog can (and actually does not) make any difference (at least not a visible one). Any insight would be appreciated.

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• What is the typical method to separate connected letters in a word using OCR

  - by Maysam

  I am very new to OCR and almost know nothing about the algorithms used to recognize words. I am just getting familiar to that. Could anybody please advise on the typical method used to recognize and separate individual characters in connected form (I mean in a word where all letters are linked together)? Forget about handwriting, supposing the letters are connected together using a known font, what is the best method to determine each individual character in a word? When characters are written separately there is no problem, but when they are joined together, we should know where every single character starts and ends in order to go to the next step and match them individually with a letter. Is there any known algorithm for that?

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• What are some C++ Standard Library usage best practices?

  - by apphacker

  I'm learning C++ and the book I'm reading (The C++ Programming Language) says to not reinvent the wheel, to rely on the standard libraries. In C, I often end up creating a linked list, and link list iteration over and over again (maybe I'm doing that wrong not sure), so the ideas of containers available in C++, and strings, and algorithms really appeal to me. However I have read a little online, and heard some criticisms from my friends and coworkers about STL, so I thought I maybe I'd pick some brains here. What are some best practices for using STL, and what lessons have you learned about STL?

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• Is Work Stealing always the most appropriate user-level thread scheduling algorithm?

  - by Il-Bhima

  I've been investigating different scheduling algorithms for a thread pool I am implementing. Due to the nature of the problem I am solving I can assume that the tasks being run in parallel are independent and do not spawn any new tasks. The tasks can be of varying sizes. I went immediately for the most popular scheduling algorithm "work stealing" using lock-free deques for the local job queues, and I am relatively happy with this approach. However I'm wondering whether there are any common cases where work-stealing is not the best approach. For this particular problem I have a good estimate of the size of each individual task. Work-stealing does not make use of this information and I'm wondering if there is any scheduler which will give better load-balancing than work-stealing with this information (obviously with the same efficiency). NB. This question ties up with a previous question.

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• Dealing with passwords securely

  - by Krt_Malta

  Hi I have a Java web service and a Java web client making use of this service. One of the functions is to create a new user account. My two concerns are: How will I send the user's password securely from the client. How will I store the user's password securely on the server. How can I achieve these? I know the theory basically behind security, security algorithms etc but can anyone give me some advice on how I should go about in coding? Could anyone point me to some good (and if possible not complicated) examples to follow since I found some examples on the Internet very contorted? Thanks a lot and regards, Krt_Malta

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• What is better for a student programming in C++ to learn for writing GUI: C# vs QT?

  - by flashnik

  I'm a teacher(instructor) of CS in the university. The course is based on Cormen and Knuth and students program algorithms in C++. But sometimes it is good to show how an algorithm works or just a result of task through GUI. Also in my opinion it's very imporant to be able to write full programs. They will have courses concerning GUI but a three years, later, in fact, before graduatuion. I think that they should be able to write simple GUI applications earlier. So I want to teach them it. How do you think, what is more useful for them to learn: programming GUI with QT or writing GUI in C# and calling unmanaged C++ library?

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• Determine if a string contains only alphanumeric characters (or a space)

  - by dreamlax

  I'm learning C++ and I am writing a function that determines whether a string contains only alphanumeric characters and spaces. I suppose I am effectively testing whether it matches the regular expression ^[[:alnum:] ]+$ but without using regular expressions. I have seen a lot of algorithms revolve around iterators, so I tried to find a solution that made use of iterators, and this is what I have: #include <algorithm> static inline bool is_not_alnum_space(char c) { return !(isalpha(c) || isdigit(c) || (c == ' ')); } bool string_is_valid(const std::string &str) { return find_if(str.begin(), str.end(), is_not_alnum_space) == str.end(); } Is there a better solution, or a “more C++” way to do this?

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• Algorithm for non-contiguous netmask match

  - by Gianluca

  Hi, I have to write a really really fast algorithm to match an IP address to a list of groups, where each group is defined using a notation like 192.168.0.0/252.255.0.255. As you can see, the bitmask can contain zeros even in the middle, so the traditional "longest prefix match" algorithms won't work. If an IP matches two groups, it will be assigned to the group containing most 1's in the netmask. I'm not working with many entries (let's say < 1000) and I don't want to use a data structure requiring a large memory footprint (let's say 1-2 MB), but it really has to be fast (of course I can't afford a linear search). Do you have any suggestion? Thanks guys. UPDATE: I found something quite interesting at http://www.cse.usf.edu/~ligatti/papers/grouper-conf.pdf, but it's still too memory-hungry for my utopic use case

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• bluetooth emulators/simulators

  - by scatman

  what are the best bluetooth emulators/simulators? i have a project for the security course, and i chose bluetooth as my topic. so i need to create encryption algorithms using a bluetooth simulator and test them. i have already searched for the best emulaters, and the results were google anroid, and NS2. is there any emulator better? the languages i prefer to program with are c , c++ , and c# java is also not a problem but i prefer any of the above languages.

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• Algorithm to match natural text in mail

  - by snøreven

  I need to separate natural, coherent text/sentences in emails from lists, signatures, greetings and so on before further processing. example: Hi tom, last monday we did bla bla, lore Lorem ipsum dolor sit amet, consectetur adipisici elit, sed eiusmod tempor incidunt ut labore et dolore magna aliqua. list item 2 list item 3 list item 3 Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquid x ea commodi consequat. Quis aute iure reprehenderit in voluptate velit regards, K. ---line-of-funny-characters-####### example inc. 33 evil street, london mobile: 00 234534/234345 Ideally the algorithm would match only the bold parts. Is there any recommended approach - or are there even existing algorithms for that problem? Should I try approximate regular expressions or more statistical stuff based on number of punctation marks, length and so on?

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• Fastest way of converting a quad to a triangle strip?

  - by Tina Brooks

  What is the fastest way of converting a quadrilateral (made up of foyr x,y points) to a triangle strip? I'm well aware of the general triangulation algorithms that exist, but I need a short, well optimized algorithm that deals with quadrilaterals only. My current algorithm does this, which works for most quads but still gets the points mixed up for some: #define fp(f) bounds.p##f /* Sort four points in ascending order by their Y values */ point_sort4_y(&fp(1), &fp(2), &fp(3), &fp(4)); /* Bottom two */ if (fminf(-fp(1).x, -fp(2).x) == -fp(2).x) { out_quad.p1 = fp(2); out_quad.p2 = fp(1); } else { out_quad.p1 = fp(1); out_quad.p2 = fp(2); } /* Top two */ if (fminf(-fp(3).x, -fp(4).x) == -fp(3).x) { out_quad.p3 = fp(3); out_quad.p4 = fp(4); } else { out_quad.p3 = fp(4); out_quad.p4 = fp(3); }

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• best method of turning millions of x,y,z positions of particles into visualisation

  - by Griff

  I'm interested in different algorithms people use to visualise millions of particles in a box. I know you can use Cloud-In-Cell, adaptive mesh, Kernel smoothing, nearest grid point methods etc to reduce the load in memory but there is very little documentation on how to do these things online. i.e. I have array with: x,y,z 1,2,3 4,5,6 6,7,8 xi,yi,zi for i = 100 million for example. I don't want a package like Mayavi/Paraview to do it, I want to code this myself then load the decomposed matrix into Mayavi (rather than on-the-fly rendering) My poor 8Gb Macbook explodes if I try and use the particle positions. Any tutorials would be appreciated.

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• Remove from a std::set<shared_ptr<T>> by T*

  - by Autopulated

  I have a set of shared pointers: std::set<boost::shared_ptr<T>> set; And a pointer: T* p; I would like to efficiently remove the element of set equal to p, but I can't do this with any of the members of set, or any of the standard algorithms, since T* is a completely different type to boost::shared_ptr<T>. A few approaches I can think of are: somehow constructing a new shared_ptr from the pointer that won't take ownership of the pointed to memory (ideal solution, but I can't see how to do this) wrapping / re-implementing shared_ptr so that I can do the above just doing my own binary search over the set Help!

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• Is there a name for the technique of using base-2 numbers to encode a list of unique options?

  - by Lunatik

  Apologies for the rather vague nature of this question, I've never been taught programming and Google is rather useless to a self-help guy like me in this case as the key words are pretty ambiguous. I am writing a couple of functions that encode and decode a list of options into a Long so they can easily be passed around the application, you know this kind of thing: 1 - Apple 2 - Orange 4 - Banana 8 - Plum etc. In this case the number 11 would represent Apple, Orange & Plum. I've got it working but I see this used all the time so assume there is a common name for the technique, and no doubt all sorts of best practice and clever algorithms that are at the moment just out of my reach.

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• What's the best way to match a query to a set of keywords?

  - by Ryan Detzel

  Pretty much what you would assume Google does. Advertisers come in and big on keywords, lets say "ipod", "ipod nano", "ipod 60GB", "used ipod", etc. Then we have a query, "I want to buy an ipod nano" or "best place to buy used ipods" what kind of algorithms and systems are used to match those queries to the keyword set. I would imagine that some of those keyword sets are huge, 100k keywords made up of one or more actual words. on top of that queries can be 1-n words as well. Any thoughts, links to wikipedia I can start reading? From what I know already I would use some stemmed hash in disk(CDB?) and a bloom filter to check to see if I should even go to disk.

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• What is it about Fibonacci numbers?

  - by Ian Bishop

  Fibonacci numbers have become a popular introduction to recursion for Computer Science students and there's a strong argument that they persist within nature. For these reasons, many of us are familiar with them. They also exist within Computer Science elsewhere too; in surprisingly efficient data structures and algorithms based upon the sequence. There are two main examples that come to mind: Fibonacci heaps which have better amortized running time than binomial heaps. Fibonacci search which shares O(log N) running time with binary search on an ordered array. Is there some special property of these numbers that gives them an advantage over other numerical sequences? Is it a density quality? What other possible applications could they have? It seems strange to me as there are many natural number sequences that occur in other recursive problems, but I've never seen a Catalan heap.

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• Direct video card access

  - by icemanind

  Guys, I am trying to write a class in C# that can be used as a direct replacement for the C# Bitmap class. What I want to do instead though is perform all graphic functions done on the bitmap using the power of the video card. From what I understand, functions such as DrawLine or DrawArc or DrawText are primitive functions that use simple cpu math algorithms to perform the job. I, instead, want to use the graphics card cpu and memory to do these and other advanced functions, such as skinning a bitmap (applying a texture) and true transparancy. My problem is, in C#, how do I access direct video functions? Is there a library or something I need?

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• Google Suggest - What determines the sort order of suggested queries on google?

  - by John Himmelman

  How is this sort order determined? Is it ranked by popularity, number of results, or a mysterious google algorithm? Does there algorithm take into account the search popularity of a query (using google-trends data or something)? Edit: I found a news article dating back to when google suggest was made public in 2004. Here is an excerpt... How does it work? "Our algorithms use a wide range of information to predict the queries users are most likely to want to see. For example, Google Suggest uses data about the overall popularity of various searches to help rank the refinements it offers." Source: http://www.free-seo-news.com/newsletter138.htm

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• Merging photo textures - (from calibrated cameras) - projected onto geometry

  - by freakTheMighty

  I am looking for papers/algorithms for merging projected textures onto geometry. To be more specific, given a set of fully calibrated cameras/photographs and geometry, how can we define a metric for choosing which photograph should be used to texture a given patch of the geometry. I can think of a few attributes one may seek minimize including the angle between the surface normal and the camera, the distance of the camera from the surface, as well as minimizing some parameterization of sharpness. The question is how do these things get combined and are there well established existing solutions?

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• Using a locale-dependent sorting function in Ruby/Rails

  - by knuton

  What is a good approach to sorting an array of strings in accordance with the current locale? For example the standard Array#sort puts "Ä" after "Z", which is not correct in German. I would have expected the gem I18n to offer a hook for defining my own sorting algorithms or providing collation strings or objects. In my imagination, passing this proc or string to the sort function, would make it behave as necessary. I know that this is possible in Python, for example. Google has not helped me this time. Can you? Any advice appreciated!

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• Level of Detail for 3D terrains/models in Mobile Devices (Android / XNA )

  - by afriza

  I am planning to develop for WP7 and Android. What is the better way to display (and traverse) 3D scene/models in term of LoD? The data is planned to be island-wide (Singapore). 1) Real-Time Dynamic Level of Detail Terrain Rendering 2) Discrete LoD 3) Others? And please advice some considerations/algorithms/resources/source codes. something like LoD book also Okay. Side note: I am a beginner in this area but pretty well-versed in C/C++. And I haven't read the LoD book. Related posts: - Distant 3D object rendering [games]

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• What should I do to practice?

  - by simion

  I start a year long industrial placement in September where i will be coding in Java predominantly. I am going to use the summer to brush up on my Java as in year one of the degree Java was the main language taught for OOP modules. However this year i have had no Java exposure except for an algorithms module, which was one of eight, so as you can see i am probably getting really rusty!. What i wanted to know is, how does the "real world" java programming differ from university coding and what do you suggest i brush up on that would be different to my normal workings. As a start I definitely need to get familiar with a professional IDE like NetBeans, opposed to having used BlueJ throughout but more specifically what coding practices should I get more familiar with. I appreciate they wont expect me to be a qualified full developer and will give me time, but I would like to hit the ground running as it were, with me having full hopes to secure a permanent position after I finish my degree.

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• How to create digital signature that can not be used to reproduce the message twice

  - by freediver

  I am creating a client-server application and I'd like to send data from server to client securely. Using public/private key algorithms makes sense and in PHP we can use openssl_sign and openssl_verify functions to check that the data came by someone who has the private key. Now imagine that one of the actions sent by server to client is destructive in nature. If somebody uses an HTTP sniffer to catch this command (which will be signed properly) how can I further protect the communication to ensure that only commands coming from our server get processed by the client? I was thinking about using current UTC time as part of the encrypted data but client time might be off. Is there a simple solution to the problem?

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• O(log N) == O(1) - Why not?

  - by phoku

  Whenever I consider algorithms/data structures I tend to replace the log(N) parts by constants. Oh, I know log(N) diverges - but does it matter in real world applications? log(infinity) < 100 for all practical purposes. I am really curious for real world examples where this doesn't hold. To clarify: I understand O(f(N)) I am curious about real world examples where the asymptotic behaviour matters more than the constants of the actual performance. If log(N) can be replaced by a constant it still can be replaced by a constant in O( N log N). This question is for the sake of (a) entertainment and (b) to gather arguments to use if I run (again) into a controversy about the performance of a design.

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• Lua: Random: Percentage

  - by jargl

  I'm creating a game and currently have to deal with some math.randomness. As I'm not that strong in Lua, how do you think Can you make an algorithm that uses math.random with a given percentage? I mean a function like this: function randomChance( chance ) -- Magic happens here -- Return either 0 or 1 based on the results of math.random end randomChance( 50 ) -- Like a 50-50 chance of "winning", should result in something like math.random( 1, 2 ) == 1 (?) randomChance(20) -- 20% chance to result in a 1 randomChance(0) -- Result always is 0 However I have no clue how to go on, and I completely suck at algorithms I hope you understood my bad explanation of what I'm trying to accomplish

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