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  • Longest Common Subsequence

    - by tsudot
    Consider 2 sequences X[1..m] and Y[1..n]. The memoization algorithm would compute the LCS in time O(m*n). Is there any better algorithm to find out LCS wrt time? I guess memoization done diagonally can give us O(min(m,n)) time complexity.

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  • posmax: like argmax but gives the position(s) of the element x for which f[x] is maximal

    - by dreeves
    Mathematica has a built-in function ArgMax for functions over infinite domains, based on the standard mathematical definition. The analog for finite domains is a handy utility function. Given a function and a list (call it the domain of the function), return the element(s) of the list that maximize the function. Here's an example of finite argmax in action: http://stackoverflow.com/questions/471029/canonicalize-nfl-team-names/472213#472213 And here's my implementation of it (along with argmin for good measure): (* argmax[f, domain] returns the element of domain for which f of that element is maximal -- breaks ties in favor of first occurrence. *) SetAttributes[{argmax, argmin}, HoldFirst]; argmax[f_, dom_List] := Fold[If[f[#1]>=f[#2], #1, #2]&, First[dom], Rest[dom]] argmin[f_, dom_List] := argmax[-f[#]&, dom] First, is that the most efficient way to implement argmax? What if you want the list of all maximal elements instead of just the first one? Second, how about the related function posmax that, instead of returning the maximal element(s), returns the position(s) of the maximal elements?

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  • Discovering a functional algorithm from a mutable one

    - by Garrett Rowe
    This isn't necessarily a Scala question, it's a design question that has to do with avoiding mutable state, functional thinking and that sort. It just happens that I'm using Scala. Given this set of requirements: Input comes from an essentially infinite stream of random numbers between 1 and 10 Final output is either SUCCEED or FAIL There can be multiple objects 'listening' to the stream at any particular time, and they can begin listening at different times so they all may have a different concept of the 'first' number; therefore listeners to the stream need to be decoupled from the stream itself. Pseudocode: if (first number == 1) SUCCEED else if (first number >= 9) FAIL else { first = first number rest = rest of stream for each (n in rest) { if (n == 1) FAIL else if (n == first) SUCCEED else continue } } Here is a possible mutable implementation: sealed trait Result case object Fail extends Result case object Succeed extends Result case object NoResult extends Result class StreamListener { private var target: Option[Int] = None def evaluate(n: Int): Result = target match { case None => if (n == 1) Succeed else if (n >= 9) Fail else { target = Some(n) NoResult } case Some(t) => if (n == t) Succeed else if (n == 1) Fail else NoResult } } This will work but smells to me. StreamListener.evaluate is not referentially transparent. And the use of the NoResult token just doesn't feel right. It does have the advantage though of being clear and easy to use/code. Besides there has to be a functional solution to this right? I've come up with 2 other possible options: Having evaluate return a (possibly new) StreamListener, but this means I would have to make Result a subtype of StreamListener which doesn't feel right. Letting evaluate take a Stream[Int] as a parameter and letting the StreamListener be in charge of consuming as much of the Stream as it needs to determine failure or success. The problem I see with this approach is that the class that registers the listeners should query each listener after each number is generated and take appropriate action immediately upon failure or success. With this approach, I don't see how that could happen since each listener is forcing evaluation of the Stream until it completes evaluation. There is no concept here of a single number generation. Is there any standard scala/fp idiom I'm overlooking here?

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  • What "exotic" language feature do you use every day?

    - by fmark
    For most programmers using procedural or object-oriented languages there is a language-feature lowest common denominator: variables, procedures, standard control structures, and classes. However, almost all languages add features on top of this. Recent C# versions have LINQ and delegates. C++ has template metaprogramming. Java has annotations. What features such as these do you use every day?

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  • How to change internal buffer size of DataInputStream

    - by Gaks
    I'm using this kind of code for my TCP/IP connection: sock = new Socket(host, port); sock.setKeepAlive(true); din = new DataInputStream(sock.getInputStream()); dout = new DataOutputStream(sock.getOutputStream()); Then, in separate thread I'm checking din.available() bytes to see if there are some incoming packets to read. The problem is, that if a packet bigger than 2048 bytes arrives, the din.available() returns 2048 anyway. Just like there was a 2048 internal buffer. I can't read those 2048 bytes when I know it's not the full packet my application is waiting for. If I don't read it however - it'll all stuck at 2048 bytes and never receive more. Can I enlarge the buffer size of DataInputStream somehow? Socket receive buffer is 16384 as returned by sock.getReceiveBufferSize() so it's not the socket limiting me to 2048 bytes. If there is no way to increase the DataInputStream buffer size - I guess the only way is to declare my own buffer and read everything from DataInputStream to that buffer? Regards

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  • Socket read() hangs for a while when there is no data to read.

    - by janesconference
    Hi' I'm writing a simple http port forwarder. I read data from port 80, and pass the data to my lighttpd server, on port 8080. As long as I write() data on the socket on port 8080 (forwarding the request) there's no problem, but when I read() data from that socket (forwarding the response), the last read() hangs a lot (about 1 or 2 seconds) before realizing there's no more data and returning 0. I tried to set the socket to non-blocking, but this doesn't work, as sometimes it returns EWOULDBLOCKING even if there's some data left (lighttpd + cgi can be quite slow). I tried to set a timeout with select(), but, as above, a slow cgi could timeout the socket when there's actually some data to transmit. How would you do?

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  • Where is the Open Source alternative to WPF?

    - by Evan Plaice
    If we've learned anything from HTML/CSS it's that, declarative languages (like XML) work best to describe User Interfaces because: It's easy to build code preprocessors that can template the code effectively. The code is in a well defined well structured (ideally) format so it's easy to parse. The technology to effectively parse or crawl an XML based source file already exists. The UIs scripted code becomes much simpler and easier to understand. It simple enough that designers are able to design the interface themselves. Programmers suck at creating UIs so it should be made easy enough for designers. I recently took a look at the meat of a WPF application (ie. the XAML) and it looks surprisingly familiar to the declarative language style used in HTML. It's blindingly apparent to me that the current state of desktop UI development is largely fractionalized, otherwise there wouldn't be so much duplicated effort in the domain of user interfaces (IE. GTK, XUL, Qt, Winforms, WPF, etc). There are 45 GUI platforms for Python alone It's painfully obvious to me that there should be a general purpose, open source, standardized, platform independent, markup language for designing desktop GUIs. Much like what the W3C made HTML/CSS into. WPF, or more specifically XAML seems like a pretty likely step in the right direction. Why hasn't anyone in the Open Source community (AFAIK) even scratched the surface of this issue. Now that the 'browser wars' are over should we look forward to a future of 'desktop gui wars?' Note: This topic is relatively subjective in the attempt to be 'future-thinking.' I think that desktop GUI development in its current state sucks ((really)hard) and, even though WPF is still in it's infancy, it presents a likely solution to the problem. Has no one in the OS community looked into developing something similar because they don't see the value, or because it's not worth the effort?

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  • Agile language for 2d game prototypes?

    - by instanceofTom
    Occasionally ( read: when my fiancé allows ) I like to prototype different game or game-like ideas I have. Usually I use Java or C# (not xna yet) because they are the languages I have the most practice with. However I would like to learn something more suited to agile development; a language in which it would be easier to knock out quick prototypes. At my job I have recently been working with looser (weak/dynamically typed) languages, specifically python and groovy, and I think something similar would fit what I am looking for. So, my question is: What languages (and framework/engine) would be good for rapidly developing prototypes of 2d game concepts? A few notes: I don't need blazing fast bitcrunching performance. In this case I would strongly prefer ease of development over performance. I'd like to use a language with a healthy community, which to me means a fair amount of maintained 3rd party, libraries. I'd like the language to be cross-platform friendly, I work on a variety of different operating systems and would like something that is portable with minimum effort. I can't imagine myself using a language with out decent options for debugging and editor syntax highlighting support. Note: If you are aware of a Java or C# library/framework that you think streamlines producing game prototypes I open to learning something new for those languages too

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  • (For what) Are Fortran, Cobol and Co. used today?

    - by lamas
    I'm a relatively young programmer and so I don't really know much about languages like Fortran or Cobol that have their origins in the beginning of modern informatics. I'm a bit confused because it seems like there are many people out there saying that these two languages are still very alive and being used all over the world whereas others say the opposite. In addition, it seems like there are only very few questions tagged Fortran or Cobol here on stackoverflow. Can someone "demystify" the situation for me? Who uses these senior languages these days and are they even used anymore? Do you have any experiences with one of the languages or do you know something about their latest developments?

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  • Sources for news about network security

    - by chris.nullptr
    I am a software developer that wants to stay up-to-date on network security news. What are some of the best sources online for not only keeping tabs on newly discovered security vulnerabilities that may affect projects I'm working on, but also best-practices when developing network software. Please keep in mind that I am looking for sources that cater to the software developer not IT administration.

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  • What does a linux device need to be seen by Hal?

    - by Jaime Soriano
    I'm trying to learn about device drivers on Linux Kernel, for that I've created three modules with: A bus type A device driver A fake device that does nothing now, only is registered Everything works fine, I can load the bus, the driver and the module that creates the device. Everything appears on sysfs, including the link between the device and the device driver that indicates that they are binded. And when the driver and device are loaded, I can see using udevadm monitor that also some events are provoked: KERNEL[1275564332.144997] add /module/bustest_driver (module) KERNEL[1275564332.145289] add /bus/bustest/drivers/bustest_example (drivers) UDEV [1275564332.157428] add /module/bustest_driver (module) UDEV [1275564332.157483] add /bus/bustest/drivers/bustest_example (drivers) KERNEL[1275564337.656650] add /module/bustest_device (module) KERNEL[1275564337.656817] add /devices/bustest_device (bustest) UDEV [1275564337.658294] add /module/bustest_device (module) UDEV [1275564337.664707] add /devices/bustest_device (bustest) But after everything, the device doesn't appear on hal. What else need a device to be seen by hal?

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  • Pthread-ed filetransfer application crash

    - by N.R.S.Sowrabh
    I am developing a file transfer application and am using pthreads on the receiver side for receiving multiple files. The function which is passed to pthreads calls the following function and at the end of this function I get a SIGABRT error and stack-smashing error appears on the terminal. Please help me find the bugs. If you need anymore code I'd be able to post the same. Thanks in advance. void recv_mesg(int new_sockid, char *fname) { cout<<"New Thread created with "<<new_sockid<<" and "<<fname<<endl; char buf[MAXLINE]; int fd; fd = open(fname, O_WRONLY ); int len =0; while (len<1024) { int curr = recv(new_sockid, buf, 1024-len, 0); //fprintf(stdout,"Message from Client:\n"); len += curr; //write (fd, buf, curr); fputs(buf, stderr); } int file_size = 0; sscanf(buf,"%d",&file_size); if(file_size<=0) perror("File Size < 0"); sprintf(buf,"Yes"); send(new_sockid,buf,strlen(buf),0); len = 0; while (len<file_size) { int curr = recv(new_sockid, buf, min(file_size-len,MAXLINE), 0); len += curr; write (fd, buf, curr); //fputs(buf, stdout); //fflush(stdout); } len = 0; close(fd); close(new_sockid); }

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  • What language/compiler for native running of application in any windows platform?

    - by Xinxua
    Hi, I want to develop an application that runs on any windows platform (XP, Vista, 7) but does not require a dependency like .NET Framework or JVM. I have given the other requirements below: Runs in any windows platform Must have GUI libraries to create windows/primitive controls I also want the output file size of the application to be minimal (So cannot include .net frameword etc in the exe file) Any suggestions for this requirement?

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  • C# property definition

    - by Sunny
    For C# properties, I can do this: public class Employee{ public string Name { get; private set; } public Employee(string name){ Name = name; } } which means that the Name property can be set within the class Employee & can be read publicly. But, if I want to restrict the set to only within the constructors of the Employee class, I need to do: public class Employee{ public readonly string Name = String.Empty; public Employee(string name){ Name = name; } } But, for this case, I had to change the property to a field. Is there any reason this is not possible/allowed in C#: public class Employee{ public string Name { get; private readonly set; } public Employee(string name){ Name = name; } } IMO this will allow us to have properties which can be set only in the constructor & does not require us to change properties to fields... Thanks!

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  • Conventions for the behavior of double or triple "click to select text" features?

    - by John Sullivan
    Almost any mature program that involves text implements "double click to select the word" and, in some cases, "triple click to select additional stuff like an entire line" as a feature. I find these features useful but they are often inconsistent between programs. Example - some programs' double clicks do not select the ending space after a word, but most do. Some recognize the - character as the end of a word, others do not. SO likes to select the entire paragraph as I write this post when I triple click it, VS web developer 2005 has no triple click support, and ultra-edit 32 will select one line upon triple clicking. We could come up with innumerable inconsistencies about how double and triple click pattern matching is implemented across programs. I am concerned about how to implement this behavior in my program if nobody else has achieved a convention about how the pattern matching should work. My question is, does a convention (conventions? maybe an MS or Linux convention?) exist that dictates how these features are supposed to behave to the end user? What, if any, are they?

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  • How well does Scala Perform Comapred to Java?

    - by Teja Kantamneni
    The Question actually says it all. The reason behind this question is I am about to start a small side project and want to do it in Scala. I am learning scala for the past one month and now I am comfortable working with it. The scala compiler itself is pretty slow (unless you use fsc). So how well does it perform on JVM? I previously worked on groovy and I had seen sometimes over performed than java. My Question is how well scala perform on JVM compared to Java. I know scala has some very good features(FP, dynamic lang, statically typed...) but end of the day we need the performance...

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  • Please Help me add up the elements for this structure in Scheme/Lisp

    - by kunjaan
    I have an input which is of this form: (((lady-in-water . 1.25) (snake . 1.75) (run . 2.25) (just-my-luck . 1.5)) ((lady-in-water . 0.8235294117647058) (snake . 0.5882352941176471) (just-my-luck . 0.8235294117647058)) ((lady-in-water . 0.8888888888888888) (snake . 1.5555555555555554) (just-my-luck . 1.3333333333333333))) (context: the word denotes a movie and the number denotes the weighted rating submitted by the user) I need to add all the quantity and return a list which looks something like this ((lady-in-water 2.5) (snake 2.5) (run 2.25) (just-myluck 2.6)) How do I traverse the list and all the quantities? I am really stumped. Please help me. Thanks.

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  • Recommended way to support backward/forward compatibility in iPhone app?

    - by MrAleGuy
    I'm in the early stages of an iPhone app and I have a question. I did some searching but did not find what I was looking for. There are features in iPhone OS4 that I would like to take advantage of, but I would like for my app to also run on 3.X. It looks like I want to develop against the 4.0 SDK and do the following: Create a "weak link" to any new (4.0) frameworks Call respondsToSelector: for any new method in an existing framework or any method in a new framework before making that call Am I close? What's recommended? Pointers to similar questions welcome.

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  • implementing type inference

    - by deepblue
    well I see some interesting discussions here about static vs. dynamic typing I generally prefer static typing, due to compile type checking, better documented code,etc. However I do agree that they do clutter up the code if done the way Java does it, for example. so Im about to start building a language of my own and type inference is one of the things that I want to implement, in a functional style language... I do understand that it is a big subject, and Im not trying to create something that has not been done before, just basic inferencing... any pointers on what to read up that will help me with this? preferably something more pragmatic/practical as oppose to more theoretical category theory/type theory texts. If there's a implementation discussion text out here, with data structures/algorithms, that would just be lovely much appreciated

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  • Creating a project, from Makefile to static/dynamic libraries in UNIX

    - by Sasha
    Guys, would you describe a few things about c++ building blocks, on unix. I want to create an application that links against static libs and dynamic libs (.so). Question 1: How do I create static library using gcc/g++ ?How do I make my app link against it. Question 2: How to specify it in the makefile, linking against static and dynamic libs, assuming that both libraries have header files Summary: I have been using makefiles and libraries for years, written by someone else. Thus every time I modified it, I simply cut-and-pasted things around, without really understanding it. Now I want to get down to the ground and understand the building/linking/Creating Makfile process in-depth. What is a good book describing these concepts in intimate details? Thanks

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  • Should I invest time in learning Java language these days? (question from a greenhorn)

    - by dave-keiture
    Hi experts, Assuming you've already had a chance to look through the lambda syntax proposed for Java7 (and the other things that have happened with Java, after Oracle has bought Sun + obvious problems in Java Community Process), what do you think is the future of Java language? Should I, as a Java greenhorn, invest time in learning Java language (not talking about the core JVM, which definitely will survive anything, and worth investments), or concentrate on Scala, Groovy, or other hybrid languages on the JVM platform (I've came into Java world from PHP/Ruby). Thanks in advance.

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  • Why do some languages not use semicolons and braces?

    - by Incognito
    It is interesting that some languages do not use semicolons and braces, even though their predecessors had them. Personally, it makes me nervous to write code in Python because of this. Semicolons are also missing from Google's GO language, although the lexer uses a rule to insert semicolons automatically as it scans. Why do some languages not use semicolons and braces?

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