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• A minimum spanning tree / shortest path in a directed graph

  - by mvid

  Given a directed graph with weighted edges, what algorithm can be used to give a sub-graph that has minimum weight, but allows movement from any vertex to any other vertex in the graph (under the assumption that paths between any two vertices always exist). Does such an algorithm exist?

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• Defend zero-based arrays

  - by DrJokepu

  A question asked here recently reminded me of a debate I had not long ago with a fellow programmer. Basically he argued that zero-based arrays should be replaced by one-based arrays since arrays being zero based is an implementation detail that originates from the way arrays and pointers and computer hardware work, but these sort of stuff should not be reflected in higher level languages. Now I am not really good at debating so I couldn't really offer any good reasons to stick with zero-based arrays other than they sort of feel like more appropriate. I am really interested in the opinions of other developers, so I sort of challenge you to come up with reasons to stick with zero-based arrays!

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• Programming challenge: can you code a hello world program as a Palindrome?

  - by Assaf Lavie

  So the puzzle is to write a hello world program in your language of choice, where the program's source file as a string has to be a palindrome. To be clear, the output has to be exactly "Hello, World". Edit: Well, with comments it seems trivial (not that I thought of it myself of course [sigh].. hat tip to cobbal). So new rule: no comments. Edit: I feel kind of bad editing someone else's question to say this, but it will eliminate a lot of non-palindromes that keep popping up, and I'm tired of seeing the same simple mistake over and over. The following is NOT a palindrome: ()() The following IS a palindrome: ())( Brackets, parenthesis, and anything else that must match are a major barrier to palindrome-ing, yes, but that doesn't mean you can ignore them and post non-palindrome answers. Languages represented thus far: C, C++, Bash, elisp, C#, Perl, sh, Windows shell, Java, Common Lisp, Awk, Ruby, Brainfuck, Funge, Python, Machine Language, HQ9+, Assembly, TCL, J, php, Haskell, io, TeX, APL, Javascript, mIRC Script, Basic, Orc, Fortran, Unlambda, Pseudo-code, Befunge, CFML, Lua, INTERCAL, VBScript, HTML, sed, PostScript, GolfScript, REBOL, SQL

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• What is "elegant" code?

  - by Breton

  I see a lot of lip service and talk about the most "elegant" way to do this or that. I think if you spend enough time programming you begin to obtain a sort of intuitive feel for what it is we call "elegance". But I'm curious. Even if we can look at a bit of code, and say instinctively "That's elegant", or "That's messy", I wonder if any of us really understands what that means. Is there a precise definition for this "elegance" we keep referring to? If there is, what is it? Now, what I mean by a precise definition, is a series of statements which can be used to derive questions about a peice of code, or a program as a whole, and determine objectively, or as objectively as possible, whether that code is "elegant" or not. May I assert, that perhaps no such definition exists, and it's all just personal preference. In this case, I ask you a slightly different question: Is there a better word for "elegance", or a better set of attributes to use for judging code quality that is perhaps more objective than merely appealing to individual intuition and taste? Perhaps code quality is a matter of taste, and the answer to both of my questions is "no". But I can't help but feel that we could be doing better than just expressing wishy washy feelings about our code quality. For example, user interface design is something that to a broad range of people looks for all the world like a field of study that oughtta be 100% subjective matter of taste. But this is shockingly and brutally not the case, and there are in fact many objective measures that can be applied to a user interface to determine its quality. A series of tests could be written to give a definitive and repeatable score to user interface quality. (See GOMS, for instance). Now, okay. is Elegance simply "code quality" or is it something more? Is it something that can be measured? Or is it a matter of taste? Does our profession have room for taste? Maybe I'm asking the wrong questions altogether. Help me out here. Bonus Round If there is such a thing as elegance in code, and that concept is useful, do you think that justifies classifying the field of programming as an "Art" capital A, or merely a "craft". Or is it just an engineering field populated by a bunch of wishful thinking humans? Consider this question in the light of your thoughts about the elegance question. Please note that there is a distinction between code which is considered "art" in itself, and code that was written merely in the service of creating an artful program. When I ask this question, I ask if the code itself justifies calling programming an art. Bounty Note I liked the answers to this question so much, I think I'd like to make a photographic essay book from it. Released as a free PDF, and published on some kind of on demand printing service of course, such as "zazz" or "tiggle" or "printley" or something . I'd like some more answers, please!

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• Sample application to read and inspect packets on a network?

  - by franz

  Hi, I'm looking to write a quick program to read and inspect packets of a certain format and then blacklist ips with a certain style of packet-traffic (packet patterns of an attack against the network). Are there decent samples of reading and inspecting packet flow on a network?

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• Finding what makes strings unique in a list, can you improve on brute force?

  - by Ed Guiness

  Suppose I have a list of strings where each string is exactly 4 characters long and unique within the list. For each of these strings I want to identify the position of the characters within the string that make the string unique. So for a list of three strings abcd abcc bbcb For the first string I want to identify the character in 4th position d since d does not appear in the 4th position in any other string. For the second string I want to identify the character in 4th position c. For the third string it I want to identify the character in 1st position b AND the character in 4th position, also b. This could be concisely represented as abcd -> ...d abcc -> ...c bbcb -> b..b If you consider the same problem but with a list of binary numbers 0101 0011 1111 Then the result I want would be 0101 -> ..0. 0011 -> .0.. 1111 -> 1... Staying with the binary theme I can use XOR to identify which bits are unique within two binary numbers since 0101 ^ 0011 = 0110 which I can interpret as meaning that in this case the 2nd and 3rd bits (reading left to right) are unique between these two binary numbers. This technique might be a red herring unless somehow it can be extended to the larger list. A brute-force approach would be to look at each string in turn, and for each string to iterate through vertical slices of the remainder of the strings in the list. So for the list abcd abcc bbcb I would start with abcd and iterate through vertical slices of abcc bbcb where these vertical slices would be a | b | c | c b | b | c | b or in list form, "ab", "bb", "cc", "cb". This would result in four comparisons a : ab -> . (a is not unique) b : bb -> . (b is not unique) c : cc -> . (c is not unique) d : cb -> d (d is unique) or concisely abcd -> ...d Maybe it's wishful thinking, but I have a feeling that there should be an elegant and general solution that would apply to an arbitrarily large list of strings (or binary numbers). But if there is I haven't yet been able to see it. I hope to use this algorithm to to derive minimal signatures from a collection of unique images (bitmaps) in order to efficiently identify those images at a future time. If future efficiency wasn't a concern I would use a simple hash of each image. Can you improve on brute force?

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• What is the single most effective thing you did to improve your programming skills?

  - by Oded

  Looking back at my career and life as a programmer, there were plenty of different ways I improved my programming skills - reading code, writing code, reading books, listening to podcasts, watching screencasts and more. My question is: What is the most effective thing you have done that improved your programming skills? What would you recommend to others that want to improve? I do expect varied answers here and no single "one size fits all" answer - I would like to know what worked for different people. Edit: Wow - what great answers! Keep 'em coming people!!!

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• Find location using only distance and range?

  - by pinnacler

  Triangulation works by checking your angle to three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and it's to my right at 90 degrees." Repeat 2 more times for different targets and angles. Trilateration works by checking your distance from three KNOWN targets. "I know the that's the Lighthouse of Alexandria, it's located here (X,Y) on a map, and I'm 100 meters away from that." Repeat 2 more times for different targets and ranges. But both of those methods rely on knowing WHAT you're looking at. Say you're in a forest and you can't differentiate between trees, but you know where key trees are. These trees have been hand picked as "landmarks." You have a robot moving through that forest slowly. Do you know of any ways to determine location based solely off of angle and range, exploiting geometry between landmarks? Note, you will see other trees as well, so you won't know which trees are key trees. Ignore the fact that a target may be occluded. Our pre-algorithm takes care of that. 1) If this exists, what's it called? I can't find anything. 2) What do you think the odds are of having two identical location 'hits?' I imagine it's fairly rare. 3) If there are two identical location 'hits,' how can I determine my exact location after I move the robot next. (I assume the chances of having 2 occurrences of EXACT angles in a row, after I reposition the robot, would be statistically impossible, barring a forest growing in rows like corn). Would I just calculate the position again and hope for the best? Or would I somehow incorporate my previous position estimate into my next guess? If this exists, I'd like to read about it, and if not, develop it as a side project. I just don't have time to reinvent the wheel right now, nor have the time to implement this from scratch. So if it doesn't exist, I'll have to figure out another way to localize the robot since that's not the aim of this research, if it does, lets hope it's semi-easy.

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• What are some languages that currently support mixins?

  - by leeand00

  Well obviously Ruby and Sass, but what are some other ones?

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• Where to start learning if interested in augmented reality?

  - by Terri

  I'm currently an undergrad in computer science and I'll be entering my final year next year. Augmented reality is something I find to be a really cool topic, but I have no idea where to start learning about it. Where do you start learning about this topic and what libraries are available?

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• Find all complete sub-graphs within a graph

  - by mvid

  Is there a known algorithm or method to find all complete sub-graphs within a graph? I have an undirected, unweighted graph and I need to find all subgraphs within it where each node in the subgraph is connected to each other node in the subgraph. Is there an existing algorithm for this?

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• Business Objects - Containers or functional?

  - by Walter

  Where I work, we've gone back and forth on this subject a number of times and are looking for a sanity check. Here's the question: Should Business Objects be data containers (more like DTOs) or should they also contain logic that can perform some functionality on that object. Example - Take a customer object, it probably contains some common properties (Name, Id, etc), should that customer object also include functions (Save, Calc, etc.)? One line of reasoning says separate the object from the functionality (single responsibility principal) and put the functionality in a Business Logic layer or object. The other line of reasoning says, no, if I have a customer object I just want to call Customer.Save and be done with it. Why do I need to know about how to save a customer if I'm consuming the object? Our last two projects have had the objects separated from the functionality, but the debate has been raised again on a new project. Which makes more sense? EDIT These results are very similar to our debates. One vote to one side or another completely changes the direction. Does anyone else want to add their 2 cents? EDIT Eventhough the answer sampling is small, it appears that the majority believe that functionality in a business object is acceptable as long as it is simple but persistence is best placed in a separate class/layer. We'll give this a try. Thanks for everyone's input...

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• Rot13 for numbers.

  - by dreeves

  EDIT: Now a Major Motion Blog Post at http://messymatters.com/sealedbids The idea of rot13 is to obscure text, for example to prevent spoilers. It's not meant to be cryptographically secure but to simply make sure that only people who are sure they want to read it will read it. I'd like to do something similar for numbers, for an application involving sealed bids. Roughly I want to send someone my number and trust them to pick their own number, uninfluenced by mine, but then they should be able to reveal mine (purely client-side) when they're ready. They should not require further input from me or any third party. (Added: Note the assumption that the recipient is being trusted not to cheat.) It's not as simple as rot13 because certain numbers, like 1 and 2, will recur often enough that you might remember that, say, 34.2 is really 1. Here's what I'm looking for specifically: A function seal() that maps a real number to a real number (or a string). It should not be deterministic -- seal(7) should not map to the same thing every time. But the corresponding function unseal() should be deterministic -- unseal(seal(x)) should equal x for all x. I don't want seal or unseal to call any webservices or even get the system time (because I don't want to assume synchronized clocks). (Added: It's fine to assume that all bids will be less than some maximum, known to everyone, say a million.) Sanity check: > seal(7) 482.2382 # some random-seeming number or string. > seal(7) 71.9217 # a completely different random-seeming number or string. > unseal(seal(7)) 7 # we always recover the original number by unsealing.

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• software/languages for online structured data collection from (human) clients

  - by Ben

  I need to develop a web interface to collect and validate a range of data from many of my organization's clients. This isn't a single form, but a collection of forms with interdependencies (i.e., field X on form Y is needed if field A was equal to C on form B), and variable length lists (please provide the details for all Xs in your possession). I had a look at the marketing on Microsoft InfoPath and Adobe LiveCycle, but I get the impression that they're principally electronic forms solutions rather than data collection tools. (e.g., If a user has entered their address once, they should never have to see it on a form again). Any suggestions of good tools, applications or domain-specific languages?

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• Code Golf: Diamond Pattern

  - by LiraNuna

  The challenge The shortest code by character count to output a a pattern of diamonds according to the input. The input is composed of 3 positive numbers representing the size of the diamond and the size of the grid. A diamond is made from the ASCII characters / and \ with spaces. A diamond of size 1 is: /\ \/ The size of the grid consists from width and height of number of diamonds. Test cases Input: 1 6 2 Output: /\/\/\/\/\/\ \/\/\/\/\/\/ /\/\/\/\/\/\ \/\/\/\/\/\/ Input: 2 2 2 Output: /\ /\ / \/ \ \ /\ / \/ \/ /\ /\ / \/ \ \ /\ / \/ \/ Input 4 1 3 Output: /\ /\ /\ / \ / \ / \ / \ / \ / \ / \/ \/ \ \ /\ /\ / \ / \ / \ / \ / \ / \ / \/ \/ \/ Code count includes input/output (i.e full program).

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• Based on your development stack, which is easier for you and why? Debugging or logging?

  - by leeand00

  Please state if you are developing on the front end, back end, or if you are developing a mobile/desktop application. List your development stack Language, IDE, etc.. Unit Testing or no Unit Testing Be sure to include any AOP frameworks if used. Tell me if it is easier for you to use debugging or to using logging during development, and why you feel it is easier. I'm just trying to get a feel for why people choose debugging or logging based on their development stack.

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• What's the reason for leaving an extra blank line at the end of a code file?

  - by Lord Torgamus

  Eclipse and MyEclipse create new Java files with an extra blank line after the last closing brace by default. I think CodeWarrior did the same thing a few years back, and that some people leave such blank lines in their code either by intention or laziness. So, this seems to be at least a moderately widespread behavior. As a former human language editor -- copy editing newspapers, mostly -- I find that those lines look like sloppiness or accidents, and I can't think of a reason to leave them in source files. I know they don't affect compilation in C-style languages, including Java. Are there benefits to having those lines, and if so, what are they?

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• Generating video or images of geometrical objects from data

  - by Jonathan Barbero

  Hello, I'm working in a course's project to predict the velocity and position of the solar system planets (and other objects). It will be really cool if I can visualize the predicted objects data, if it's possible generating 3D images, if in video that's amazing. Do you know any library that lets me to use this data to generate an image or video? (I don't care in which language) Data: - simulation step (time line step for a video) - positions of the objects - radius and/or colours of the objects Thanks in advance, any suggestion is welcome.

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• Encode complex number as RGB pixel and back

  - 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? Edit: Looks like I just need to convert RGB to HSB and back. Edit 2: Existing RGB - HSV converter fragment: if (hsv.sat == 0) { hsv.hue = 0; // ! return hsv; } I don't want 0. I want random. And not just if hsv.sat==0, but if it is lower that it should be ("should be" means maximum saturation, saturation that is after transformation from complex number).

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• finding two most distant elements in a binary tree

  - by attwad

  I am looking for an algorithm that could find the two most distant elements in a binary tree, not looking for any special language, just for the algorithm. Thanks.

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• Generate all unique substrings for given string

  - by Yuval A

  Given a string s, what is the fastest method to generate a set of all its unique substrings? Example: for str = "aba" we would get substrs={"a", "b", "ab", "ba", "aba"}. The naive algorithm would be to traverse the entire string generating substrings in length 1..n in each iteration, yielding an O(n^2) upper bound. Is a better bound possible? (this is technically homework, so pointers-only are welcome as well)

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• Linear feedback shift register?

  - by Mattia Gobbi

  Lately I bumped repeatedly into the concept of LFSR, that I find quite interesting because of its links with different fields and also fascinating in itself. It took me some effort to understand, the final help was this really good page, much better than the (at first) cryptic wikipedia entry. So I wanted to write some small code for a program that worked like a LFSR. To be more precise, that somehow showed how a LFSR works. Here's the cleanest thing I could come up with after some lenghtier attempts (Python): def lfsr(seed, taps): sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor sr, xor = str(xor) + sr[:-1], 0 print sr if sr == seed: break lfsr('11001001', (8,7,6,1)) #example I named "xor" the output of the XOR function, not very correct. However, this is just meant to show how it circles through its possible states, in fact you noticed the register is represented by a string. Not much logical coherence. This can be easily turned into a nice toy you can watch for hours (at least I could :-) def lfsr(seed, taps): import time sr, xor = seed, 0 while 1: for t in taps: xor += int(sr[t-1]) if xor%2 == 0.0: xor = 0 else: xor = 1 print xor print time.sleep(0.75) sr, xor = str(xor) + sr[:-1], 0 print sr print time.sleep(0.75) Then it struck me, what use is this in writing software? I heard it can generate random numbers; is it true? how? So, it would be nice if someone could: explain how to use such a device in software development come up with some code, to support the point above or just like mine to show different ways to do it, in any language Also, as theres not much didactic stuff around about this piece of logic and digital circuitry, it would be nice if this could be a place for noobies (like me) to get a better understanding of this thing, or better, to understand what it is and how it can be useful when writing software. Should have made it a community wiki? That said, if someone feels like golfing... you're welcome.

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• What is a Windows scripting language that: does not rely on .NET and offers the most OOP support and

  - by jJack

  What is a Windows scripting language that: does not rely on .NET and offers the most OOP support and has simplest deployment? It doesn't necessarily need to be a scripting language; It can be in the form of a compiled executable, however it needs to be self contained--only ONE file, no DLL's and it cannot be declared to "include" other files. I cannot rely on the user having any .NET installed and it needs to be able to run on Windows 7 64 bit. By "most OOP support", I basically mean anything that has better OOP support than VBScript. A little context: Everything I have done thus far is in VBScript and writes a bunch of data into an .html file, which in the end is to be viewed by Internet Explorer. It also zips up a bunch of directories and files. It heavily relies on accessing the registry, file-system, and WMI (I can probably do without accessing WMI though, as long as I have good registry access). I can bring myself to code in any language so long as it meets me ridonkulous requirements stated above. I look forward to some good answers from those more experienced than I.

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• Are there any strongly typed scripting languages?

  - by George Edison

  I am wondering if there are any strongly typed scripting languages. Python, JavaScript, etc. are great languages, but they are (to a certain degree) loosely typed. I am just wondering if anyone knows of any strongly typed scripting languages. And by scripting, I mean a language whose interpreter can be embedded in a C++ application.

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• Interface for classes that have nothing in common

  - by Tomek Tarczynski

  Lets say I want to make few classes to determine behaviour of agents. The good practice would be to make some common interface for them, such interface (simplified) could look like this: interface IModel { void UpdateBehaviour(); } All , or at least most, of such model would have some parameters, but parameters from one model might have nothing in common with parameters of other model. I would like to have some common way of loading parameters. Question What is the best way to do that? Is it maybe just adding method void LoadParameters(object parameters) to the IModel? Or creating empty interface IParameters and add method void LoadParameters(IParameters parameters)? That are two ideas I came up with, but I don't like either of them.

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