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  • How do you reproduce bugs that occur sporadically?

    - by furtelwart
    We have a bug in our application that does not occur every time and therefore we don't know its "logic". I don't even get it reproduced in 100 times today. Disclaimer: This bug exists and I've seen it. It's not a pebkac or something similar. What are common hints to reproduce this kind of bug?

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  • What are the lesser known but cool data structures ?

    - by f3lix
    There a some data structures around that are really cool but are unknown to most programmers. Which are they? Everybody knows linked lists, binary trees, and hashes, but what about Skip lists, Bloom filters for example. I would like to know more data structures that are not so common, but are worth knowing because they rely on great ideas and enrich a programmer's tool box. PS: I am also interested on techniques like Dancing links which make interesting use of the properties of a common data structure. EDIT: Please try to include links to pages describing the data structures in more detail. Also, try to add a couple of words on why a data structures is cool (as Jonas Kölker already pointed out). Also, try to provide one data-structure per answer. This will allow the better data structures to float to the top based on their votes alone.

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  • Placement of defensive structures in a game

    - by Martin
    I am working on an AI bot for the game Defcon. The game has cities, with varying populations, and defensive structures with limited range. I'm trying to work out a good algorithm for placing defence towers. Cities with higher populations are more important to defend Losing a defence tower is a blow, so towers should be placed reasonably close together Towers and cities can only be placed on land So, with these three rules, we see that the best kind of placement is towers being placed in a ring around the largest population areas (although I don't want an algorithm just to blindly place a ring around the highest area of population, sometime there might be 2 sets of cities far apart, in which case the algorithm should make 2 circles, each one half my total towers). I'm wondering what kind of algorithms might be used for determining placement of towers?

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  • Factorial Algorithms in different languages

    - by Brad Gilbert
    I want to see all the different ways you can come up with, for a factorial subroutine, or program. The hope is that anyone can come here and see if they might want to learn a new language. Ideas: Procedural Functional Object Oriented One liners Obfuscated Oddball Bad Code Polyglot Basically I want to see an example, of different ways of writing an algorithm, and what they would look like in different languages. Please limit it to one example per entry. I will allow you to have more than one example per answer, if you are trying to highlight a specific style, language, or just a well thought out idea that lends itself to being in one post. The only real requirement is it must find the factorial of a given argument, in all languages represented. Be Creative! Recommended Guideline: # Language Name: Optional Style type - Optional bullet points Code Goes Here Other informational text goes here I will ocasionally go along and edit any answer that does not have decent formatting.

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  • How to notice unusual news activity

    - by ??iu
    Suppose you were able keep track of the news mentions of different entities, like say "Steve Jobs" and "Steve Ballmer". What are ways that could you tell whether the amount of mentions per entity per a given time period was unusual relative to their normal degree of frequency of appearance? I imagine that for a more popular person like Steve Jobs an increase of like 50% might be unusual (an increase of 1000 to 1500), while for a relatively unknown CEO an increase of 1000% for a given day could be possible (an increase of 2 to 200). If you didn't have a way of scaling that your unusualness index could be dominated by unheard-ofs getting their 15 minutes of fame.

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  • An Ideal Keyboard Layout for Programming

    - by Jon Purdy
    I often hear complaints that programming languages that make heavy use of symbols for brevity, most notably C and C++ (I'm not going to touch APL), are difficult to type because they require frequent use of the shift key. A year or two ago, I got tired of it myself, downloaded Microsoft's Keyboard Layout Creator, made a few changes to my layout, and have not once looked back. The speed difference is astounding; with these few simple changes I am able to type C++ code around 30% faster, depending of course on how hairy it is; best of all, my typing speed in ordinary running text is not compromised. My questions are these: what alternate keyboard layouts have existed for programming, which have gained popularity, are any of them still in modern use, do you personally use any altered layout, and how can my layout be further optimised? I made the following changes to a standard QWERTY layout. (I don't use Dvorak, but there is a programmer Dvorak layout worth mentioning.) Swap numbers with symbols in the top row, because long or repeated literal numbers are typically replaced with named constants; Swap backquote with tilde, because backquotes are rare in many languages but destructors are common in C++; Swap minus with underscore, because underscores are common in identifiers; Swap curly braces with square brackets, because blocks are more common than subscripts; and Swap double quote with single quote, because strings are more common than character literals. I suspect this last is probably going to be the most controversial, as it interferes the most with running text by requiring use of shift to type common contractions. This layout has significantly increased my typing speed in C++, C, Java, and Perl, and somewhat increased it in LISP and Python.

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  • Resources needed: Sort 2D array "graphically"

    - by aw
    I have a 2D array 1 2 3 4 5 6 7 8 9 and want to sort it like this Snake 1 2 3 8 9 4 7 6 5 Snake (different) 1 2 3 6 5 4 7 8 9 Rotated 1 4 7 2 5 8 3 6 9 Wipe (diagonal) 1 3 6 2 5 8 4 7 9 Well, you got it, all kinds of sorting. Searching the interweb for hours now. Any resources (specific language or pseudo code) on that greatly appreciated...

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  • How a servlet can get the absolute path to a file outside of the servlet?

    - by WolfmanDragon
    We have been using System.getProperties("user.dir") to get the location of a properties file. Now that it has been deployed on Tomcat(via servlet), the System call is giving the location as tomcat and not at the location at where the properties file exist. How can we call the the properties file dynamically? Given: Tomcat is not the only way the app will be deployed We have no control on where the app may be placed. Relative paths will not work as that Vista is being used and Vista breaks relative paths. This must work on all OS, including(but not limited to) Linux, XP and Vista. EDIT I implied this, but in case I was not clear enough, I have no way of knowing the path String.

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  • Why should GoTos be bad?

    - by lisn
    I'm using gotos and a lot of them. C++, PHP or COBOL - I use them on nearly all occasions where everybody else would use functions or even classes. Yet my code is Clear Maintainable Bug-free Fast So why does everybody I meet tell me about how bad gotos are? Are there any facts that show that they are "bad"?

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  • Compiler Construction course

    - by donpal
    I'm looking for a course (preferably video, much preferably) like MIT's video courses on Compiler Construction. Can someone point me to some decent resources or help material (preferably video)?

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  • Why is processing a sorted array faster than an unsorted array?

    - by GManNickG
    Here is a piece of code that shows some very peculiar performance. For some strange reason, sorting the data miraculously speeds up the code by almost 6x: #include <algorithm> #include <ctime> #include <iostream> int main() { // generate data const unsigned arraySize = 32768; int data[arraySize]; for (unsigned c = 0; c < arraySize; ++c) data[c] = std::rand() % 256; // !!! with this, the next loop runs faster std::sort(data, data + arraySize); // test clock_t start = clock(); long long sum = 0; for (unsigned i = 0; i < 100000; ++i) { // primary loop for (unsigned c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } double elapsedTime = static_cast<double>(clock() - start) / CLOCKS_PER_SEC; std::cout << elapsedTime << std::endl; std::cout << "sum = " << sum << std::endl; } Without std::sort(data, data + arraySize);, the code runs in 11.54 seconds. With the sorted data, the code runs in 1.93 seconds. Initially I thought this might be just a language or compiler anomaly. So I tried it Java... import java.util.Arrays; import java.util.Random; public class Main { public static void main(String[] args) { // generate data int arraySize = 32768; int data[] = new int[arraySize]; Random rnd = new Random(0); for (int c = 0; c < arraySize; ++c) data[c] = rnd.nextInt() % 256; // !!! with this, the next loop runs faster Arrays.sort(data); // test long start = System.nanoTime(); long sum = 0; for (int i = 0; i < 100000; ++i) { // primary loop for (int c = 0; c < arraySize; ++c) { if (data[c] >= 128) sum += data[c]; } } System.out.println((System.nanoTime() - start) / 1000000000.0); System.out.println("sum = " + sum); } } with a similar but less extreme result. My first thought was that sorting brings the data into cache, but my next thought was how silly that is because the array was just generated. What is going on? Why is a sorted array faster than an unsorted array? The code is summing up some independent terms, the order should not matter.

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  • Modelling multiple simultaneous states

    - by James P.
    How can you go about modelling an object that can have multiple simultaneous states? For example, you could have a person that's waiting for a bus. That's one state. But they could also be reading a newspaper while waiting for the bus. Furthermore, they could be thinking about something while reading the newspaper. They could also be sniffing their nose because they have a cold. That's a four states in all taking place at the same time. Obviously using booleans would be tedious and unflexible. Also, a conventional state pattern would mean that states are exclusive and can't be simultaneous in nature. The only thing I can think of is a State pattern combined with a Composite. Would this do or is there a way of taking things further?

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  • Are there any good sites for blogging about programming?

    - by Jacques Bosch
    I have a few programming articles I would like to write, but I do not have a site of my own - yet ;). Is there a site that is specifically geared toward technical / programming topics, with great functionality and style? Or will I have to go with things like wordpress or blogspot? I would like a site that can track number of views and that has an intuitive commenting system. Any thoughts would be appreciated.

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  • Beginner's resources/introductions to classification algorithms.

    - by Dirk
    Hi, everybody. I am entirely new to the topic of classification algorithms, and need a few good pointers about where to start some "serious reading". I am right now in the process of finding out, whether machine learning and automated classification algorithms could be a worthwhile thing to add to some application of mine. I already scanned through "How to Solve It: Modern heuristics" by Z. Michalewicz and D. Fogel (in particular, the chapters about linear classifiers using neuronal networks), and on the practical side, I am currently looking through the WEKA toolkit source code. My next (planned) step would be to dive into the realm of Bayesian classification algorithms. Unfortunately, I am lacking a serious theoretical foundation in this area (let alone, having used it in any way as of yet), so any hints at where to look next would be appreciated; in particular, a good introduction of available classification algorithms would be helpful. Being more a craftsman and less a theoretician, the more practical, the better... Hints, anyone?

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  • Is there anyone out there that codes like I do?

    - by Jacob Relkin
    Hi, Some people have told me that my coding style is a lot different than theirs. I think I am somewhat neurotic when it comes to spacing and indenting though. Here's a snippet to show you what I mean: - ( void ) applicationDidFinishLaunching: ( UIApplication *) application { SomeObject *object = [ [ SomeObject alloc ] init ]; int x = 100 / 5; object.someInstanceVariable = ( ( 4 * x ) + rand() ); [ object someMethod ]; } Notice how I space out all of my brackets/parentheses, start curly braces on the same line, "my code has room to breathe", so to speak. So my questions are a) is this normal and b) What's your coding style?

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  • What programming language is this?

    - by Richard M.
    I recently stumbled over a very odd source listing on a rather old programming-related site (lost it somewhere in my browser history as I didn't care about it at first). I think that this is part of a simple (console-based?) snake game. I searched and searched but didn't find a language that looked somwhat like this. This seems like a mix of Python, Ruby and C++. What the hell? What programming-language is the below source listing written in? Maybe you can figure it out? my Snake.hasProps { length parts xDir yDir } & hasMethods { init: length = 0 parts[0].x,y = 5 move: parts[ 0 ].x,y.!add xDir | yDir # Move the head map parts(i,v): parts[ i ] = parts[ i + 1 ] checkBiteSelf checkFeed checkBiteSelf: part } my SnakePart.hasProps { x y } fork SnakePart to !Feed my Game.hasProps { frameTime = 30 } & hasMethods { init: mainloop mainloop: sys.util.sleep frameTime Snake.move Field.getInput -> Snake.xDir | Snake.yDir Field.reDraw with Snake & Feed & Game # For FPS } main.isMethod { game.init }

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  • Semantically linking to code snippets

    - by Tim
    What's the most simple and semantic way of presenting code snippets in HTML? Possible XHTML syntax <a href="code_sample.php" type="text/x-php"> Example of widget creation </a> Example of linked file (code_sample.php): // Create a new widget $widget = new widget(); Pros: Semantically uses title to describe the source code being referenced Up to the client to render snippet Having very many custom server-side implementations tells me it should be standardized Browsers can have plug-ins for copy+paste, download, etc Seems to me this is where it belongs (not in Javascript) Degradation: non-compliant browsers receive a link to the associated content Cons: Not semantic enough? Seems wrong to replace hyperlinks with source code for presentation <object> might be better, but wouldn't degrade as nicely. Background I'm trying to create a "personal" XHTML standard for storing notes (wow, this is probably among the nerdiest things I've said). Since notes are just "scratch" it needs to be very lightweight. SO's markdown is very lightweight but not semantic enough for my needs. Plus, now I'm just curious. What's the most ideal syntax for linking to client-rendered code-snippets?

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  • Articles about replication schemes/algorithms?

    - by jkff
    I'm designing an hierarchical distributed system (every node has zero or more "master" nodes to which it propagates its current data). The data gets continuously updated and I'd like to guarantee that at least N nodes have almost-current data at any given time. I do not need complete consistency, only eventual consistency (t.i. for any time instant, the current snapshot of data should eventually appear on at least N nodes. It is tricky to define the term "current" here, but still). Nodes may fail and go back up at any moment, and there is no single "central" node. O overflowers! Point me to some good papers describing replication schemes. I've so far found one: Consistency Management in Optimistic Replication Algorithms

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  • What turns away users/prospective users?

    - by Zach Johnson
    In your experience, what kinds of things have turned away users and prospective users from using your programs? Also, what kinds of things turn you away from using someone else's programs? For example, one thing that really bugs me is when someone provides free software, but requires you to enter your name and email address before you download it. Why do they need my name and email address? I just want to use the program! I understand that the developer(s) may want to get a feel for how many users they have, etc, but the extra work I have to do really makes me think twice about downloading their software, even if it does really great things.

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  • What is the most efficient way to store a mapping "key -> event stream"?

    - by jkff
    Suppose there are ~10,000's of keys, where each key corresponds to a stream of events. I'd like to support the following operations: push(key, timestamp, event) - pushes event to the event queue for key, marked with the given timestamp. It is guaranteed that event timestamps for a particular key are pushed in sorted or almost sorted order. tail(key, timestamp) - get all events for key since the given timestamp. Usually the timestamp requests for a given key are almost monotonically increasing, almost synchronously with pushes for the same key. This stuff has to be persistent (although it is not absolutely necessary to persist pushes immediately and to keep tails with pushes strictly in sync), so I'm going to use some kind of database. What is the optimal kind of database structure for this task? Would it be better to use a relational database, a key-value storage, or something else?

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  • How could it happen that version control software emerged so lately?

    - by sharptooth
    According to Wikipedia (the table at the page bottom), the earliest known version control systems were CVS and TeamWare both known from year 1990. How can it be? Software development has been here from at most 1960's and I honestly can't imagine working with codebase without version control. How could it happen that version control software emerged so lately compared to software development?

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