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• Optimality of Binary Search

  - by templatetypedef

  Hello all- This may be a silly question, but does anyone know of a proof that binary search is asymptotically optimal? That is, if we are given a sorted list of elements where the only permitted operation on those objects is a comparison, how do you prove that the search can't be done in o(lg n)? (That's little-o of lg n, by the way.) Note that I'm restricting this to elements where the only operation permitted operation is a comparison, since there are well-known algorithms that can beat O(lg n) on expectation if you're allowed to do more complex operations on the data (see, for example, interpolation search). Thanks so much! This has really been bugging me since it seems like it should be simple but has managed to resist all my best efforts. :-)

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• Why are there two implementations of std::sort (with and without a comparator) rather than one implementation with a default template parameter?

  - by PolyVox

  In my code I'm adopting a design strategy which is similar to some standard library algorithms in that the exact behavior can be customized by a function object. The simplest example is std::sort, where a function object can control how the comparison is made between objects. I notice that the Visual C++ provides two implementations of std::sort, which naturally involves code duplication. I would have imagined that it was instead possible to have only one implementation, and provide a default comparator (using operator< ) as a default template parameter. What is the rational behind two separate versions? Would my suggestion make the interface more complex in some way? Or result in confusing error messages when the object does not provide operator Thanks, David

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• Creating a computer with pencil and paper [closed]

  - by Justian Meyer

  This concept has been brought to my attention before, but many people might know it from this popular comic here, where he uses stones instead of points on a paper. This concept is so abstract to me. A full-functioning computer that can manage algorithms, input, output, etc. without electricity? Surely, it's difficult to visualize because my definition of a computer is not exactly what the word sounds like COMPUTE-ER. Can someone help me bring the concept to light - the understanding, how to make one, etc? It seems like it'd be an interesting read, although I think I wouldn't be able to make it do anything. Many thanks in advance for responses. I've tried searching Google, but all I got were ways to diagram code and chart ideas. -.Justian.

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• What are the core mathematical concepts a good developer should know?

  - by Jose B.

  Since Graduating from a very small school in 2006 with a badly shaped & outdated program (I'm a foreigner & didn't know any better school at the time) I've come to realize that I missed a lot of basic concepts from a mathematical & software perspective that are mostly the foundations of other higher concepts. I.e. I tried to listen/watch the open courseware from MIT on Introduction to Algorithms but quickly realized I was missing several mathematical concepts to better understand the course. So what are the core mathematical concepts a good software engineer should know? And what are the possible books/sites you will recommend me?

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• Information Modeling

  - by Betamoo

  The sensor module in my project consists of a rotating camera, that collects noisy information about moving objects in the surrounding environment. The information consists of distance, angle and relative change of the moving objects.. The limiting view range of the camera makes it essential to rotate the camera periodically to update environment information... I was looking for algorithms / ways to model these information, in order to be able to guess / predict / learn motion properties of these object.. My current proposed idea is to store last n snapshots of each object in a queue. I take weighted average of positions and velocities of moving object, but I think it is a poor method... Can you state some titles that suit this case? Thanks

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• Create unique file name and fetching it to commandline argument

  - by user343934

  Hi everyone, I am working on python right now and i am little bit stuck in performing some tricks. I have web form with two options- File upload and textarea, i can easily pass file name with file upload options but have problem when it's textarea. Because when i use textarea then first i have to save values passed from textarea to some files and save it on the working directory. After that i can execute commandline argument and pass same saved filename name. For this problem i have to generate unique file first and save the values passed from textarea in it. Can anybody give me some tips to solve my problem. Any algorithms, suggestions and lines of code are appreciated. Thanks for your concern

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• How Can I Implement This In Java?

  - by davit-datuashvili

  first of all i am doing programs in java language this code is merely taken from web site i have not question about divide and conqurer algorithms but about function and it's argument here is code of ternary search def ternarySearch(f, left, right, absolutePrecision): #left and right are the current bounds; the maximum is between them if (right - left) < absolutePrecision: return (left + right)/2 leftThird = (2*left + right)/3 rightThird = (left + 2*right)/3 if f(leftThird) < f(rightThird): return ternarySearch(f, leftThird, right, absolutePrecision) return ternarySearch(f, left, rightThird, absolutePrecision) i am not asking once again how implement it in java i am asking for example how define function?for example let y=x^+3 yes we can determine it as public static int y(int x){ return x*x+3; } but here return ternarySearch(f, leftThird, right, absolutePrecision) function f does not have argument and how do such?please help me

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• Returning and instance of a Class given its .class (MyClass.class)

  - by jax

  I have an enum that will hold my algorithms. I cannot instantiate these classes because I need the application context which is only available once the application has started. I want to load the class at runtime when I choose by calling getAlgorithm(Context cnx). How do I easily instantiate a class at runtime given its .class (and my constructor takes arguments)? All my classes are subclasses of Algorithm. public enum AlgorithmTypes { ALL_FROM_9_AND_LAST_FROM_10_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), ALL_FROM_9_AND_LAST_FROM_10_CURRENCY_ID(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), DIVIDE_BY_9_LESS_THAN_100(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class), TABLES_BEYOND_5_BY_5(AlgorithmFactory.AlgorithmAllFrom9AndLastFrom10Impl.class); private Class<? extends Algorithm> algorithm; AlgorithmTypes(Class<? extends Algorithm> c) { algorithm = c; } public Algorithm getAlgorithm(Context cnx) { return //needs to return the current algoriths constructor which takes the Context Algorithm(Context cnx); } }

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• Analyze big human database

  - by Neir0

  Lets we have a big people database. Each human has a many parameters: age, weight, favorite music, favorite films, education etc. I want to know how one feature associate with other features. For example, if human has a good education what it means for musical preferences? Or how films preferences changes with age? I know about assotian rules algorithms like apriory but i donnt want just to found assotiation rules, i want to know how one specific feature affect to others. Which keywords i must to use for google?

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• Geographic obstructions in radius searches

  - by Michael Papile

  Suppose I have an application a search for all gas stations within 10 mile radius of a certain location. However one side of this location is surrounded by a mountain range that you have to drive 50 miles to get around. You would not want to return results from the other side of the mountain. What are some good algorithms/techniques to deal with such a problem? I know with point to point searches you can use path costs but I am not sure what the technique is with radius searches.

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• Solving a recurrence T(n) = 2T(n/2) + n^4

  - by user563454

  I am studying using the MIT Courseware and the CLRS book Introduction to Algorithms. Solving recurrence T(n) = 2T(n/2) + n4 (page 107) If I make a recurrence tree I get: level 0 n^4 level 1 2(n/2)^4 level 2 4(n/4)^4 level 3 8(n/8)^4 The tree has lg(n) levels. Therefore the recurrence is T(n) = Theta(lg(n)n^4)) But, If I use the Master method I get. Apply case 3: T(n) = Theta(n^4) If I apply the substitution method both seem to hold. Which one is ri?

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• Finding a Eulerian Tour

  - by user590903

  I am trying to solve a problem on Udacity described as follows: # Find Eulerian Tour # # Write a function that takes in a graph # represented as a list of tuples # and return a list of nodes that # you would follow on an Eulerian Tour # # For example, if the input graph was # [(1, 2), (2, 3), (3, 1)] # A possible Eulerian tour would be [1, 2, 3, 1] I came up with the following solution, which, while not as elegant as some of the recursive algorithms, does seem to work within my test case. def find_eulerian_tour(graph): tour = [] start_vertex = graph[0][0] tour.append(start_vertex) while len(graph) > 0: current_vertex = tour[len(tour) - 1] for edge in graph: if current_vertex in edge: if edge[0] == current_vertex: current_vertex = edge[1] else: current_vertex = edge[0] graph.remove(edge) tour.append(current_vertex) break return tour graph = [(1, 2), (2, 3), (3, 1)] print find_eulerian_tour(graph) >> [1, 2, 3, 1] However, when submitting this, I get rejected by the grader. I am doing something wrong? I can't see any errors.

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• Finding if a string is an iterative substring?

  - by EsotericMe

  I have a string S. How can I find if the string follows S = nT. Examples: Function should return true if 1) S = "abab" 2) S = "abcdabcd" 3) S = "abcabcabc" 4) S = "zzxzzxzzx" But if S="abcb" returns false. I though maybe we can repeatedly call KMP on substrings of S and then decide. eg: for "abab": call on KMP on "a". it returns 2(two instances). now 2*len("a")!=len(s) call on KMP on "ab". it returns 2. now 2*len("ab")==len(s) so return true Can you suggest any better algorithms?

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• Programming Exercises for Learning Purposes?

  - by cam

  Are there any programming exercises that apply to any language? Before I got my first job, I thought I knew C# pretty well, then I was thrown right into the deep end, and now I know I have a good command over the language. I would like to apply the same method to other languages, but unfortunately, I'm sort of stuck with C# at work. Ideally, something similar (but broader in scope) to Project Euler is ideal. Project Euler helped me learn a ton of C++/F#, some math, algorithms, handling bignums, etc. I'm looking for something like this.

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• public (static) swap() method vs. redundant (non-static) private ones...

  - by Helper Method

  I'm revisiting data structures and algorithms to refresh my knowledge and from time to time I stumble across this problem: Often, several data structures do need to swap some elements on the underlying array. So I implement the swap() method in ADT1, ADT2 as a private non-static method. The good thing is, being a private method I don't need to check on the parameters, the bad thing is redundancy. But if I put the swap() method in a helper class as a public static method, I need to check the indices every time for validity, making the swap call very unefficient when many swaps are done. So what should I do? Neglect the performance degragation, or write small but redundant code?

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• In which document do file specifications belong?

  - by Andrew

  In which document would a file specification belong? Perhaps this file is used as an input to a third-party system. Would it belong in its own document? Or would it be better to put it in the functional or design spec? Or somewhere else? When I say file specification, I mean a description of what format the file is (CSV, fixed width, etc), columns, data types, etc. Also, where should you document how the file is generated? i.e. business rules/algorithms which are used to generate the file.

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• How to implement low pass filter using java

  - by chai

  Hello Everyone, I am trying to implement a low pass filter in Java. My requirement is very simple,I have to eliminate signals beyond a particular frequency (Single dimension). Looks like Butterworth filter would suit my need. Now the important thing is that CPU time should be as low as possible. There would be close to a million sample the filter would have to process and our users don't like waiting too long. Are there any readymade implementation of Butterworth filters which has optimal algorithms for filtering. Regards, Chaitannya

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• Is there a way to intersect/diff a std::map and a std::set?

  - by Jack

  I'm wondering if there a way to intersect or make the differences between two structures defined as std::set<MyData*> and std::map<MyData*, MyValue> with standard algorithms (like std::set_intersect) The problem is that I need to compute the difference between the set and the keyset of the map but I would like to avoid reallocating it (since it's something that is done many times per second with large data structures). Is there a way to obtain a "key view" of the std::map? After all what I'm looking is to consider just the keys when doing the set operation so from an implementation point it should be possible but I haven't been able to find anything.

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• Multithreaded update of multiple ProgressBars

  - by ClaudeS

  I have developped an application that can process data (in my case image algorithms performed on videos). I have developed different ProcessingMethods. Sometimes several videos are processed in parallel. Each process runs in a seperate thread. I have a GUI with several ProgressBars, one for each thread that is processing data. What is a good way to update the ProgressBar? Today my GUI is creating all the processing threads and one progressBars for each thread. Then I pass those progressBars to the threads, which pass them to the ProcessingMethod. The ProcessingMethod will then update the progressbar (using Invoke(..)). I have different processingMethods. Within each of these methods I have copy-paste code to update the progressBar. Although I am a new to programming, I know copy-paste is not good. What is a good way to make it better?

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• (Secure) alternative to TLS / SSLv3 ?

  - by CSkau

  Toying with an idea for a F2F networked application I've just been reading up on secure communication. I quickly settled with the idea of using TLS / SSL as the basis for any communication since it employs Public Key encryption at the protocol level and thus is perfect for my needs. However I was surprised to read (on wikipedia) that the newest version of TLS, SSLv3 uses a mix of MD5 and SHA-1 "because if any vulnerability was found in one of these algorithms the other would prevent it from compromising SSLv3". However, as I take it, lately both have been found flawed ! So my questions are thus: Does this not mean that SSLv3 is basically flawed, or am I not reading close enough ? And if so does a "secure" alternative to SSLv3 exist ?

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• How to secure an API written in .Net

  - by The Diamond Z

  This is a variation on an existing question in SO about securing/obfuscating .Net applications in general. I'm developing an API in C# that includes some algorithms I'm keen to protect. I understand no method will be perfect, but what's the generally accepted method for doing this? I'd like my clients to be able to code against the API but I don't want them to reverse engineer what's inside (at least I don't want to make it easy for them). If I obfuscate the code, won't that also obfuscate the API? We're looking at smartAssembly any thoughts comments on the product would be appreciated.

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• Creative Technical Interview Questions for Developers

  - by John Shedletsky

  I do a good number of in-person technical interviews for new developers. I like to ask technical questions where I ask people to either code something up or develop an algorithm to solve a task. I feel my current repertoire is uninspired. In my opinion, the ideal interview question has these qualities: Multiple solutions, where some are obviously better than others, and some that involve subtle trade-offs (discussing tradeoffs is a good way to gauge someone's experience, in my opinion). Novelty - asking the "insert this element into a linked list" question is only good for weeding out people who never did their homework. Elegant - I like questions where the core problem isn't hidden in a lot of details. Everyone should be able to understand the problem, even if everyone can't solve it on the whiteboard. Elegant questions are difficult without involving undue amounts of "domain knowledge" or getting too narrow. Have you been on either side of an interview where someone (maybe you!) asked a particularly good programming or algorithms question?

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• Which language should I learn to create a sudoku game?

  - by Brandan

  I'd like to learn a new programming language, something besides all the scripting languages I've used for the past many years (Ruby, JavaScript, Perl, PHP, bash). I figured it might be interesting to make a sudoku game since there are plenty of documented algorithms and it only requires fairly simple data structures. It might start out as either a generator or a solver of puzzles, not necessarily both and not necessarily with a GUI. My goal is primarily to learn some new programming concepts beyond MVC and UI design, secondarily for this thing to be pretty fast. Is there a language that particularly shines for these sorts of constraint satisfaction problems? Is it suited to a functional language like Haskell or a highly concurrent language like Erlang (say for solving puzzles much larger than 9 x 9)? Or is this question mostly meaningless?

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• super-space-optimized code

  - by Will

  There are key self-contained algorithms - particularly cryptography-related such as AES, RSA, SHA1 etc - which you can find many implementations of for free on the internet. Some are written to be nice and portable clean C. Some are written to be fast - often with macros, and explicit unrolling. As far as I can tell, none are trying to be especially super-small - so I'm resigned to writing my own - explicitly AES128 decryption and SHA1 for ARM THUMB2. What patterns and tricks can I use to do so? Are there compilers/tools that can roll-up code?

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• How can I make a boring project (another WordPress site) interesting?

  - by Christopher Altman

  WordPress is my example, but the question can be generalized to any technology that is not particularly interesting. To me, WordPress takes away the intellectually gratifying pieces of coding. I would rather write a new version of WordPress than write a WordPress theme and glue together some plugins. I am using WP because my company dictates the platform for some of our clients (I do not disagree with the choice from a business perspective, WP is quick and cheap to implement). My question is, how can I make my next WordPress project interesting? I want to advance my understanding of the fundamentals of programming (aka data structures, algorithms, and caching) but do not see how I can achieve this when coding another WP site. I have a fairly tight understanding of front-end technologies and believe I have made WP do things it was never intended to do. Examples are here and here. Solving front-end related problems is not as interesting as coding a full stack application. Any advice will help.

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