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  • What "already invented" algorithm did you invent?

    - by Guy
    In my question Insert Update stored proc on SQL Server I explained an efficient way of doing an insert/update - perhaps THE most efficient. It's nothing amazing but it's a small algorithm that I came up with in a mini-Eureka moment. Although I had "invented" it by myself and secretly hoped that I was the first to do so I knew that it had probably been around for years but after posting on a couple of lists and not getting confirmation I had never found anything definitive written up about it. So my questions: What software algorithm did you come up with that you thought that you'd invented? Or better yet, did you invent one?

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  • Good implementations of reinforced learning?

    - by Paperino
    For an ai-class project I need to implement a reinforcement learning algorithm which beats a simple game of tetris. The game is written in Java and we have the source code. I know the basics of reinforcement learning theory but was wondering if anyone in the SO community had hands on experience with this type of thing. What would your recommended readings be for an implementation of reinforced learning in a tetris game? Are there any good open source projects that accomplish similar things that would be worth checking out? Thanks in advanced Edit: The more specific the better, but general resources about the subject are welcomed. Follow up: Thought it would be nice if I posted a followup. Here's the solution (code and writeup) I ended up with for any future students :). Paper / Code

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  • To Throw or Not to Throw

    - by serhio
    // To Throw void PrintType(object obj) { if(obj == null) { throw new ArgumentNullException("obj") } Console.WriteLine(obj.GetType().Name); } // Not to Throw void PrintType(object obj) { if(obj != null) { Console.WriteLine(obj.GetType().Name); } } What principle to keep? Personally Personally I prefer the first one its say developer-friendly. The second one its say user-friendly. What do you think?

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  • Encode complex number as RGB pixel

    - by Vi
    How is it better to encode a complex number into RGB pixel and vice versa? Probably (logarithm of) an absolute value goes to brightness and an argument goes to hue. Desaturated pixes should receive randomized argument in reverse transformation. Something like: 0 - (0,0,0) 1 - (255,0,0) -1 - (0,255,255) 0.5 - (128,0,0) i - (255,255,0) -i - (255,0,255) (0,0,0) - 0 (255,255,255) - e^(i * random) (128,128,128) - 0.5 * e^(i *random) (0,128,128) - -0.5 Are there ready-made formulas for that?

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  • Artistic aspects of UI?

    - by anon
    Consider a single button. At one extreme, we have a black OpenGL window, with: outline (in white) of a rectangle bitmap remdered font inside of it, saying "Ok" At the other extreme, we have Mac OS X, a button that is: well rounded has some gradient showing light effects on it nice antialiased "OK" soft shadow of some sort These two UIs present very very different user experiences. The former says "This is from the 80s" the latter says "this is professional". This is something I do not understand well as a programmer (and don't know where to learn about this). Does anyone know of a good technical resource for this? [I'd prefer things that draws upon psychology / perception literature to say why to do something rather than design books that just says "use color XYZ with a gradient of blah"]

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  • Wondering how Facebook does the "Mutual friends" feature

    - by Pierre
    Hello, I'm currently developing an application to allow students to manage their courses, and I don't really know how to design the database for a specific feature. The client wants, a lot like Facebook, that when a student displays the list of people currently in a specific course, the people with the most mutual courses are displayed first. As an additional feature, I would like to add a search feature to allow students to search for another one, and displaying first in the search results the people with most mutual courses. I currently use MySQL, I plan to use Cassandra for some other features, and I also use Memcached for result caching. Thanks.

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  • Any Open Source Pregel like framework for distributed processing of large Graphs?

    - by Akshay Bhat
    Google has described a novel framework for distributed processing on Massive Graphs. http://portal.acm.org/citation.cfm?id=1582716.1582723 I wanted to know if similar to Hadoop (Map-Reduce) are there any open source implementations of this framework? I am actually in process of writing a Pseudo distributed one using python and multiprocessing module and thus wanted to know if someone else has also tried implementing it. Since public information about this framework is extremely scarce. (A link above and a blog post at Google Research)

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  • Algorithm to fill slots

    - by Peter Lang
    I am searching for an algorithm to fill several slots, which are already filled to some level. The current levels and the available quantity to fill are known Resulting levels should be as equal as possible, but existing level cannot be reduced Slots are filled from left to right, so left slots get higher level if equal level is impossible       The image above shows six examples, each column represents a slot. The grey area is already filled, the blue are is the expected position of the new elements. I could iterate through my slots and increase the quantity on the lowest slot by 1 until the available quantity is consumed, but I wonder about how to actually calculate the new filling levels. I am going to implement this with SQL/PL/SQL, other code is just as welcome though :)

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  • ER Diagram flaws

    - by spacker_lechuck
    I have the following ER Diagram for a bank database - customers may have several accounts, accounts may be held jointly by several customers, and each customer is associated with an account set and accounts are members of one or more account sets. What design rules are violated? What modifications should be made and why? So far, a few flaws I'm not sure about are: 1) Redundant owner-address attribute in AcctSets Entity. 2) This ER does not include accounts with multiple owners with different addresses. My Question is: How would I go about fixing these flaws and/or other flaws that I may be missing from my analysis? Thanks!

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  • What is the best way to attach static methods to classes rather than to instances of a class?

    - by John Gietzen
    If I have a method for calculating the greatest common divisor of two integers as: public static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } What would be the best way to attach that to the System.Math class? Here are the three ways I have come up with: public static int GCD(this int a, int b) { return b == 0 ? a : b.GCD(a % b); } // Lame... var gcd = a.GCD(b); and: public static class RationalMath { public static int GCD(int a, int b) { return b == 0 ? a : GCD(b, a % b); } } // Lame... var gcd = RationalMath.GCD(a, b); and: public static int GCD(this Type math, int a, int b) { return b == 0 ? a : typeof(Math).GCD(b, a % b); } // Neat? var gcd = typeof(Math).GCD(a, b); The desired syntax is Math.GCD since that is the standard for all mathematical functions. Any suggestions? What should I do to get the desired syntax?

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  • Looking for examples of "real" uses of continuations

    - by Sébastien RoccaSerra
    I'm trying to grasp the concept of continuations and I found several small teaching examples like this one from the Wikipedia article: (define the-continuation #f) (define (test) (let ((i 0)) ; call/cc calls its first function argument, passing ; a continuation variable representing this point in ; the program as the argument to that function. ; ; In this case, the function argument assigns that ; continuation to the variable the-continuation. ; (call/cc (lambda (k) (set! the-continuation k))) ; ; The next time the-continuation is called, we start here. (set! i (+ i 1)) i)) I understand what this little function does, but I can't see any obvious application of it. While I don't expect to use continuations all over my code anytime soon, I wish I knew a few cases where they can be appropriate. So I'm looking for more explicitely usefull code samples of what continuations can offer me as a programmer. Cheers!

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  • What is technically more advanced: Python or Assembler? [closed]

    - by el ka es
    I wondered which of these languages is more powerful. With powerful I don't mean the readability, assembler would be naturally the winner here, but something resulting from, for example, the following factors: Which of them is more high-level? (Both aren't really but one has to be more) Who would be the possibly fastest in compiled state? (There is no Python compiler out there as far as I know but it wouldn't be hard writing one I suppose) Which of the both has the better code length/code action ratio? What I mean is If you get to distracted by the, compared to Python, improved readability of assembler, just think of writing plain binary/machine code as what assembler assembles to. Both languages are so basic that it should be possible to answer the question(s) in a rather objective view, I hope.

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  • Custom UITableviewcell shows "fatal error: Can't unwrap Optional.None" issue in swift

    - by user1656286
    I need to load a custom cell in a UITableView. I created a custom subclass of UITableViewCell named "CustomTableViewCell". I have added a UITabelViewCell to the tableview (using drag and drop) as shown in figure. Then in file inspector I set the class of that UITabelViewCell to be "CustomTableViewCell". Here is my code: class ViewController: UIViewController,UITableViewDelegate,UITableViewDataSource { @IBOutlet var tableView : UITableView var items = String[]() override func viewDidLoad() { super.viewDidLoad() items = ["Hi","Hello","How"] self.tableView.registerClass(CustomTableViewCell.self, forCellReuseIdentifier: "CusTomCell") // Do any additional setup after loading the view, typically from a nib. } func tableView(tableView: UITableView!, numberOfRowsInSection section: Int) -> Int{ return items.count } func tableView(tableView: UITableView!, cellForRowAtIndexPath indexPath: NSIndexPath!) -> UITableViewCell!{ var cell:CustomTableViewCell = self.tableView.dequeueReusableCellWithIdentifier("CusTomCell") as CustomTableViewCell cell.labelTitle.text = items[indexPath.row] return cell; } override func didReceiveMemoryWarning() { super.didReceiveMemoryWarning() // Dispose of any resources that can be recreated. } } When I run my code, I get the following error: "fatal error: Can't unwrap Optional.None" as seen in the image.

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  • Best graphical source code diff viewer/editor for code comparison and merging?

    - by Assaf Lavie
    The options for source code diff viewing/editing/merging seem to be: Free: Tortoise Merge Meld * WinDiff WinMerge * DiffMerge * KDiff AJC Diff Commercial: Total Commander's Diff viewer * Beyond Compare * Delta Walker * Araxis Merge * Are there any other options? (Wikipedia suggests a few) What's your favorite tools for source code diff? And how does it differ from the ones in the list? * Supports directory diffs

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  • Genetic Programming Online Learning

    - by Lirik
    Has anybody seen a GP implemented with online learning rather than the standard offline learning? I've done some stuff with genetic programs and I simply can't figure out what would be a good way to make the learning process online. Please let me know if you have any ideas, seen any implementations, or have any references that I can look at.

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  • Do you still limit line length in code?

    - by Noldorin
    This is a matter on which I would like to gauge the opinion of the community: Do you still limit the length of lines of code to a fixed maximum? This was certainly a convention of the past for many languages; one would typically cap the number of characters per line to a value such as 80 (and more recnetly 100 or 120 I believe). As far as I understand, the primary reasons for limiting line length are: Readability - You don't have to scroll over horizontally when you want to see the end of some lines. Printing - Admittedly (at least in my experience), most code that you are working on does not get printed out on paper, but by limiting the number of characters you can insure that formatting doesn't get messed up when printed. Past editors (?) - Not sure about this one, but I suspect that at some point in the distant past of programming, (at least some) text editors may have been based on a fixed-width buffer. I'm sure there are points that I am still missing out, so feel free to add to these... Now, when I tend to observe C or C# code nowadays, I often see a number of different styles, the main ones being: Line length capped to 80, 100, or even 120 characters. As far as I understand, 80 is the traditional length, but the longer ones of 100 and 120 have appeared because of the widespread use of high resolutions and widescreen monitors nowadays. No line length capping at all. This tends to be pretty horrible to read, and I don't see it too often, though it's certainly not too rare either. Inconsistent capping of line length. The length of some lines are limited to a fixed maximum (or even a maximum that changes depending on the file/location in code), while others (possibly comments) are not at all. My personal preference here (at least recently) has been to cap the line length to 100 in the Visual Studio editor. This means that in a decently sized window (on a non-widescreen monitor), the ends of lines are still fully visible. I can however see a few disadvantages in this, especially when you end up writing code that's indented 3 or 4 levels and then having to include a long string literal - though I often take this as a sign to refactor my code! In particular, I am curious what the C and C# coders (or anyone who uses Visual Studio for that matter) think about this point, though I would be interested in hearing anyone's thoughts on the subject. Edit Thanks for the all answers - I appreciate the variety of opinions here, all presenting sound reasons. Consensus does seem to be tipping in the direction of always (or almost always) limit the line length. Interestingly, it seems to be in various coding standards to limit the line length. Judging by some of the answers, both the Python and Google CPP guidelines set the limit at 80 chars. I haven't seen anything similar regarding C# or VB.NET, but I would be curious to see if there are ones anywhere.

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  • Determining whether values can potentially match a regular expression, given more input

    - by Andreas Grech
    I am currently writing an application in JavaScript where I'm matching input to regular expressions, but I also need to find a way how to match strings to parts of the regular expressions. For example: var invalid = "x", potentially = "g", valid = "ggg", gReg = /^ggg$/; gReg.test(invalid); //returns false (correct) gReg.test(valid); //returns true (correct) Now I need to find a way to somehow determine that the value of the potentially variable doesn't exactly match the /^ggg$/ expression, BUT with more input, it potentially can! So for example in this case, the potentially variable is g, but if two more g's are appended to it, it will match the regular expression /^ggg$/ But in the case of invalid, it can never match the /^ggg$/ expression, no matter how many characters you append to it. So how can I determine if a string has or doesn't have potential to match a particular regular expression?

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  • Resources for Programmatic Rendering of Topology Maps

    - by bn
    Servus, Do you know of any frameworks, APIS, languages, or other resources that are well suited for drawing topology maps that allow a user to interact with objects on the map? I am not constrained by language choice and the program can be web-based, or stand-alone. I thought I would check before rolling my own. My goal is not to draw cartographic maps, but more like this picture: http://www.fineconnection.com/files/images/GraphicalNM.PNG, or if you are familiar with Edward Tufte's books, the data-visualization mechanisms he describes such as a map of a metro or subway. Also, if you have had any experience rendering these types of user interfaces or usage of underlying datastructures, I would be grateful to hear any thoughts you have on the subject, advice, any "gotchas." Thank you very for your time, -bn

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  • The whole point of programming is creating abstractions

    - by Damien
    Hullo, this is Damien. I am new to programming and to StackOverflow community. Our professor once said that "the whole point of programming is creating abstractions." His explanation however went right over my head. Please explain the meaning of this sentence in simple words -- something that a noob like me can understand. Thank you!

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  • How do i start with Gomoku?

    - by firstTry
    I read about Gomoku that it can be implemented using Minimax and Alpha-Beta Pruning algorithms. So, i read these algorithms and now understand how the game will be solved. But when i sat to down to code, I am facing problem how to approach it. As in , How to design the prototype functions like getNextMove or Max(Move) ? How will the next move searched? Till when should i apply the minimax algorithm. I know i can find the code online, but i want to do it myself. Can anyone please point me in the right direction?

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