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  • Finding recurrence relations of an algorithm

    - by Roarke
    I'm reading my algorithms text book, and I'm reading about recurrence relations and finding the algorithms big O complexity. I run across this line "In the case of the merge-sort algorithm, we get the recurrence equation: t(n) = b if n < 2 = 2t(n/2) +bn if n >= 2 for b > 0 my response was "how the heck did we know that?!?!" So i'm wondering if there is a systematic approach, or just a logical way of getting these recurrence relations from the algorithms can some one explain where the b and the two 2's come from?

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  • Thread Local Memory for Scratch Memory.

    - by Hassan Syed
    I am using Protocol Buffers and OpensSSL to generate, HMACs and then CBC encrypt the two fields to obfuscate the session cookies -- similar Kerberos tokens. Protocol Buffers' API communicates with std::strings and has a buffer caching mechanism; I exploit the caching mechanism, for successive calls in the the same thread, by placing it in thread local memory; additionally the OpenSSL HMAC and EVP CTX's are also placed in the same thread local memory structure ( see this question for some detail on why I use thread local memory and the massive amount of speedup it enables even with a single thread). The generation and deserialization, "my algorithms", of these cookie strings uses intermediary void *s and std::strings and since Protocol Buffers has an internal memory retention mechanism I want these characteristics for "my algorithms". So how do I implement a common scratch memory ? I don't know much about the rdbuf of the std::string object. I would presumeably need to grow it to the lowest common size ever encountered during the execution of "my algorithms". Thoughts ?

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  • Programming cookbook? [closed]

    - by user73669
    Possible Duplicate: What is the single most influential book every programmer should read? Hello With sites like The Daily WTF and recurring threads on Slashdot and elsewhere about bad programming, I figured that, to avoid people reinventing the wheel (badly or not), there should be a good, fat book on programming that would go through typical programming problems and show good, known algorithms, either in pseudo-code or some language with an easy syntax so that the language is not an issue. Here's the list of books on the subject I saw at my local computer bookstore. Can you recommend a couple, or add to this list if it's missing better options? The art of computer programming Code complete Masterminds of programming 97 things every programmer should know The passionate programmer Pragmatic thinking & learning Coders at work The algorithm design manual Algorithms and programming How to think about algorithms How to think like a programmer Why programs fail Beautiful data Beautiful code The productive programmer Solid code Write great code Clean code Programming language pragmatics Hello world Learning Processing Learn to program Thank you.

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  • Finding patterns in Puzzle games.

    - by José Joel.
    I was wondering, which are the most commonly used algorithms applied to finding patterns in puzzle games conformed by grids of cells. I know that depends of many factors, like the kind of patterns You want to detect, or the rules of the game...but I wanted to know which are the most commonly used algorithms in that kind of problems... For example, games like columns, bejeweled, even tetris. I also want to know if detecting patterns by "brute force" ( like , scanning all the grid trying to find three adyacent cells of the same color ) is significantly worst that using particular algorithms in very small grids, like 4 X 4 for example ( and again, I know that depends of the kind of game and rules ...) Which structures are commonly used in this kind of games ?

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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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  • Which parallel sorting algorithm has the best average case performance?

    - by Craig P. Motlin
    Sorting takes O(n log n) in the serial case. If we have O(n) processors we would hope for a linear speedup. O(log n) parallel algorithms exist but they have a very high constant. They also aren't applicable on commodity hardware which doesn't have anywhere near O(n) processors. With p processors, reasonable algorithms should take O(n/p log n/p) time. In the serial case, quick sort has the best runtime complexity on average. A parallel quick sort algorithm is easy to implement (see here and here). However it doesn't perform well since the very first step is to partition the whole collection on a single core. I have found information on many parallel sort algorithms but so far I have not seen anything pointing to a clear winner. I'm looking to sort lists of 1 million to 100 million elements in a JVM language running on 8 to 32 cores.

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  • Non-perfect maze generation algorithm

    - by Shylux
    I want to generate a maze with the following properties: The maze is non-perfect. Means it has loops and multiple ways to reach the exit. The maze should be random. The algorithm should output different mazes for different input parameters The maze doesn't have to be braided. Means dead-ends are allowed and appreciated. I just can't find the right resources on google. The closest i found was this description of the different types of algorithms: http://www.astrolog.org/labyrnth/algrithm.htm. All other algorithms were for perfect mazes. Can anyone give me a website where i can look this up or maybe an algorithm directly?

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  • HPC Server Dynamic Job Scheduling: when jobs spawn jobs

    - by JoshReuben
    HPC Job Types HPC has 3 types of jobs http://technet.microsoft.com/en-us/library/cc972750(v=ws.10).aspx · Task Flow – vanilla sequence · Parametric Sweep – concurrently run multiple instances of the same program, each with a different work unit input · MPI – message passing between master & slave tasks But when you try go outside the box – job tasks that spawn jobs, blocking the parent task – you run the risk of resource starvation, deadlocks, and recursive, non-converging or exponential blow-up. The solution to this is to write some performance monitoring and job scheduling code. You can do this in 2 ways: manually control scheduling - allocate/ de-allocate resources, change job priorities, pause & resume tasks , restrict long running tasks to specific compute clusters Semi-automatically - set threshold params for scheduling. How – Control Job Scheduling In order to manage the tasks and resources that are associated with a job, you will need to access the ISchedulerJob interface - http://msdn.microsoft.com/en-us/library/microsoft.hpc.scheduler.ischedulerjob_members(v=vs.85).aspx This really allows you to control how a job is run – you can access & tweak the following features: max / min resource values whether job resources can grow / shrink, and whether jobs can be pre-empted, whether the job is exclusive per node the creator process id & the job pool timestamp of job creation & completion job priority, hold time & run time limit Re-queue count Job progress Max/ min Number of cores, nodes, sockets, RAM Dynamic task list – can add / cancel jobs on the fly Job counters When – poll perf counters Tweaking the job scheduler should be done on the basis of resource utilization according to PerfMon counters – HPC exposes 2 Perf objects: Compute Clusters, Compute Nodes http://technet.microsoft.com/en-us/library/cc720058(v=ws.10).aspx You can monitor running jobs according to dynamic thresholds – use your own discretion: Percentage processor time Number of running jobs Number of running tasks Total number of processors Number of processors in use Number of processors idle Number of serial tasks Number of parallel tasks Design Your algorithms correctly Finally , don’t assume you have unlimited compute resources in your cluster – design your algorithms with the following factors in mind: · Branching factor - http://en.wikipedia.org/wiki/Branching_factor - dynamically optimize the number of children per node · cutoffs to prevent explosions - http://en.wikipedia.org/wiki/Limit_of_a_sequence - not all functions converge after n attempts. You also need a threshold of good enough, diminishing returns · heuristic shortcuts - http://en.wikipedia.org/wiki/Heuristic - sometimes an exhaustive search is impractical and short cuts are suitable · Pruning http://en.wikipedia.org/wiki/Pruning_(algorithm) – remove / de-prioritize unnecessary tree branches · avoid local minima / maxima - http://en.wikipedia.org/wiki/Local_minima - sometimes an algorithm cant converge because it gets stuck in a local saddle – try simulated annealing, hill climbing or genetic algorithms to get out of these ruts   watch out for rounding errors – http://en.wikipedia.org/wiki/Round-off_error - multiple iterations can in parallel can quickly amplify & blow up your algo ! Use an epsilon, avoid floating point errors,  truncations, approximations Happy Coding !

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  • Does Google use any “Language” flags / tags set within a PDF file when determining its language?

    - by Ally Ak
    When determining the language of a HTML page, I understand that Google looks at any language declarations that the page owner has set, and then also applies its own language detection algorithms. But does Google similarly look at language meta data set in PDF files when determining a PDF file's language? (Authors of PDF files can set document-wide properties describing the language (or languages) contained within it.) Or does Google rely exclusively on language detection algorithms and disregard the language flag set within the PDF file? Can anyone shed any light?

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  • Gilda Garretón, a Java Developer and Parallelism Computing Researcher

    - by Yolande
    In a new interview titled “Gilda Garretón, a Java Developer and Parallelism Computing Research,” Garretón shares her first-hand experience developing with Java and Java 7 for very large-scale integration (VLSI) of computer-aided design (CAD). Garretón gives an insightful overview of how Java is contributing to the parallelism development and to the Electric VLSI Design Systems, an open source VLSI CAD application used as a research platform for new CAD algorithms as well as the research flow for hardware test chips.  Garretón considers that parallelism programming is hard and complex, yet important developments are taking place.  "With the addition of the concurrent package in Java SE 6 and the Fork/Join feature in Java SE 7, developers have a chance to rely more on existing frameworks and dedicate more time to the essence of their parallel algorithms." Read the full article here  

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  • Pathfinding Java library

    - by Shivan Dragon
    I'm an amateur game developer and somewhat amateur Java developer as well. I'm trying to find a way to have path finding for my game(s). I've first googled for some existing Java libraries that have various path-finding implementations, but I've failed to find any. It seems to me that the only way to get pathfinding code is to use it via a game engine (like Unity). But I'd just like to have a library that I can use and make the game loop and other stuff on my own. Failing to find such a library I've tried implementing some algorithms myself. I've managed to make a running AStar in Java, but for fancier stuff like DStar I find it hard to do it by hand. So then, my question is, are there any Java libraries that contain at least some basic pathfinding algorithms implementations?

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  • Modified Strategy Design Pattern

    - by Samuel Walker
    I've started looking into Design Patterns recently, and one thing I'm coding would suit the Strategy pattern perfectly, except for one small difference. Essentially, some (but not all) of my algorithms, need an extra parameter or two passed to them. So I'll either need to pass them an extra parameter when I invoke their calculate method or store them as variables inside the ConcreteAlgorithm class, and be able to update them before I call the algorithm. Is there a design pattern for this need / How could I implement this while sticking to the Strategy Pattern? I've considered passing the client object to all the algorithms, and storing the variables in there, then using that only when the particular algorithm needs it. However, I think this is both unwieldy, and defeats the point of the strategy pattern. Just to be clear I'm implementing in Java, and so don't have the luxury of optional parameters (which would solve this nicely).

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  • Stack vs queue -based programming language efficiency [closed]

    - by Core Xii
    Suppose there are two programming languages; one where the only form of storage is one (preferred) or two (may be required for Turing-completeness) stacks, and another where the only form of storage is a single queue, with appropriate instructions in each to manipulate their respective storage to achieve Turing-completeness. Which one can more efficiently encode complex algorithms? Such that most given algorithms take less code to implement, less time to compute and less memory to do so. Also, how do they compare to a language with a traditional array (or unbounded tape, if you will) as storage?

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  • Pathfinding library

    - by Shivan Dragon
    I'm an amateur game developer and somewhat amateur Java developer as well. I'm trying to find a way to have path finding for my game(s). I've first Googled for some existing Java libraries that have various path-finding implementations, but I've failed to find any. It seems to me that the only way to get pathfinding code is to use it via a game engine (like Unity). But I'd just like to have a library that I can use and make the game loop and other stuff on my own. Failing to find such a library I've tried implementing some algorithms myself. I've managed to make a running A* in Java, but for fancier stuff like D* I find it hard to do it by hand. So then, my question is, are there any Java libraries that contain at least some basic pathfinding algorithms implementations?

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  • Web and Flex developer career question [closed]

    - by abhilashm86
    Possible Duplicate: should i concentrate on logical and puzzles part in programming, i want to be a web (flex)developer? I'm a computer science student and have been learning Flex and Actionscript 3.0 for 4 months. I know it's easy to program in MXML, and Actionscript 3.0 is pretty easy with bunch of classes, but when I try to code in C++ or C, I struggle, I feel I'm being inefficient and it scares me. Since I'm a student, I've no experience in developing algorithms and tough program solving? I'd like to be a web developer. Does a web developer need strong fundamentals when it comes to things such as complex algorithms and high end coding?

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  • Learning Python is good?

    - by user15220
    Recently I have seen some videos from MIT on computer programming topics. I found it's really worth watching. Especially the concepts of algorithms and fundamental stuffs. The programs were written and explained in Python. I never had looked into this language before as I learned and doing stuffs with C/C++ programming. But the cleanliness and better readability of syntax attracted me. Of course as a C++ programmer for long time it's the most readable language for me. Also I heard Python library contains solid algorithms and data-structures implementations. Can you share your experience in this language?

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  • Why do programmers write n=O(n^2)?

    - by Jaakko Seppälä
    I studied algorithms in a book Cormen & al. "Introduction to algorithms". In the fourth printing, on the page 43 defines O(g(n))={f(n):there exists positive constants c and n_0 s.t. 0<=f(n)<=cg(n) for all n=n_0} I reported this as a bug in the book www-site because this leads to notation like n=O(n^2) and suggested alternative given in http://www.artofproblemsolving.com/Forum/viewtopic.php?f=296&t=31517&start=20 . It looks like my bug report has not been accepted. Why the programmers won't renew the notation?

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  • Truly Random Numbers

    German researchers use a "flip-flop" to improve random number generator Random number generation - Algorithms - Pseudorandom Numbers - Math - Recreation

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  • Career guidance/advice for Junior-level Software Engineer [closed]

    - by John Do
    I have quite a few questions on my mind, so please bare with me. Please don't feel obligated to answer all of them, any as you choose will do. I'd appreciate if you could share some insight on any of these. Before I begin, some context: I currently have almost two years of professional experience as a Software Engineer, mainly developing software in Java. At this point, I feel that I have reached the peak in my career growth at the current company I am at and therefore I am looking for a new job, ideally again, as a Software Engineer. I have been interviewing for the past few months casually but have not had luck with companies I have a passion for. So, in no particular order - 1) In general, what are your thoughts on having graduate degrees in CS / Software Engineering. How much does it influence a salary increase, and do you think it's beneficial when working on real-world problems? I get the sense that a graduate degree in the field is trivial unless you really have a passion for research. 2) In general, in professional practice, how often had you have to write your own data structures and "complex" algorithms from scratch? In my own work, I have found myself relying mainly on third-party frameworks and the Java standard library to implement solutions as per business requirements. What are your thoughts on this? 3) In terms of resume, I feel the most ambivalent here. I want to be able to "blemish" my resume to a certain extent so that it stands out from others', but at the same time I do not want to over-exagerate my abilities. How do you strike a balance here? For example: I say that I am proficient in Java with data structures and algorithms. This is obviously a subjective and relative statement. I've taken the classes in my undergrad, and I've applied it in my work experience. What I feel as "prociency" can be seen as junior-level to others. How do you know what to say? Most of the time, recruiters (with no technical background) will be looking for keywords that stand out. This leads me to my next question (4). 4) Just from interviewing for the past few months (and getting plenty of rejections), I've come to realize that I may not be as proficient in data structures and algorithms as I thought I was. Do you think it's a good idea to remove the "proficient in java/data structure and algorithms"? I feel that being too hoenst on the resume will impede me from scoring opportunities to even have an interview with top-notch companies. What are your thoughts? 5) What is the absolute "must-have" knowledge going into a technical interview? I've been practicing several algorithmic and data sturcture problems now, and I feel that my abilities to solve arbitrary problems efficiently has not gotten significantly better. Do you think these abilities are something innate - it's either you have in you, or you don't? How can you teach yourself to learn, if you will? 6) How easy is it to go from industry/function to the next? I work mainly with backend technologies and I'm now interested in working with the frontend, i.e javascript,jquery,php or even mobile development. In your own experience, how did you not get pidgeon holed in your career? I feel that the choices you make now ultimately decide your future. As cliche as it sounds, I think it may be true. Here's what I mean: you've worked mainly as a backend engineer, people are interested in you doing the same thing since you've already accumulated experience in that function. How do get experience in a new function if people won't accept you because you don't already have it? It's a catch 22, you see... Are side projects the only real way to help you move from one function to another that you're truly interested in? For example: I could start writing my own mobile applications, even though I've worked mainly on the backend. Thanks so much for the long read. As a relatively new engineer to the real world, I am very humble and would like those who are experienced to shed some light. Thank you so much.

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  • Skills to Focus on to land Big 5 Software Engineer Position

    - by Megadeth.Metallica
    Guys, I'm in my penultimate quarter of grad school and have a software engineering internship lined up at a big 5 tech company. I have dabbled a lot recently in Python and am average at Java. I want to prepare myself for coding interviews when I apply for new grad positions at the Big 5 tech companies when I graduate at the end of this year. Since I want to have a good shot at all 5 companies (Amazon,Google,Yahoo,Microsoft and Apple) - Should I focus my time and effort on mastering and improving my Java. Or is my time better spent checking out other languages and tools ( Attracted to RoR, Clojure, Git, C# ) I am planning to spend my spring break implementing all the common algorithms and Data structure out of my algorithms textbook in Java.

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  • Procedural object generation and unique identification

    - by 2080
    My question relates to procedural content generation and data management of the emerging objects in a database. I assume a networked game, with a server-client model. Unspecified objects in the game world are generated while the game is running with procedural algorithms (for example perlin noise). The players (/clients) can modify the properties of these objects, but have to notify the server of these changes. How could this communication address unique objects, so that both the server and the client know of which object they are speaking? Not only the inner properties of the objects can differ, but also visible, such as the position. When the player wants to select one of these objects the game has to find out the id - does anyone know which methods or algorithms can accomplish that?

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  • What are some good, simple examples for queues?

    - by Michael Ekstrand
    I'm teaching CS2 (Java and data structures), and am having some difficulty coming up with good examples to use when teaching queues. The two major applications I use them for are multithreaded message passing (but MT programming is out of scope for the course), and BFS-style algorithms (and I won't be covering graphs until later in the term). I also want to avoid contrived examples. Most things that I think of, if I were actually going to solve them in a single-threaded fashion I would just use a list rather than a queue. I tend to only use queues when processing and discovery are interleaved (e.g. search), or in other special cases like length-limited buffers (e.g. maintaining last N items). To the extent practical, I am trying to teach my students good ways to actually do things in real programs, not just toys to show off a feature. Any suggestions of good, simple algorithms or applications of queues that I can use as examples but that require a minimum of other prior knowledge?

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  • Education path advice

    - by Miroslav Zadravec
    I'm thinking of continuing my education and going for masters degree. I must decide between two programs. One is CS/IT and focuses on algorithms, math, multimedia, web technologies with optional interesting courses like AI and robotics. Second is about business process management, software architecture and project management. I have some experience in business software and I must say, I never though I need deeper understating of algorithms or program language but I always felt that I'm lacking in project planing or management knowledge. On the other side, CS/IT looks more interesting but what are the chances to find a job that require such skills?

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  • What does a programmer really need to become a professional?

    - by Dehumanizer
    There are huge numbers of programmers, especially juniors, who need good assistance in becoming professional. I've heard a lot of about "books every programmer should read", etc. I have two years of programming experience, feel good in C++, but currently have a strange feeling, that I do not know anything about programming. I should read Algorithms by Cormen, Code Complete by McConnell etc., but I don't know the exact steps required to become a professional. What should we do? What should we learn? Operating systems? Computer organization? Algorithms? C++ in depth? How much time do we have to spend to become what we want?

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