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• Drawing Directed Acyclic Graphs: Minimizing edge crossing?

  - by Robert Fraser

  Laying out the verticies in a DAG in a tree form (i.e. verticies with no in-edges on top, verticies dependent only on those on the next level, etc.) is rather simple without graph drawing algorithms such as Efficient Sugimiya. However, is there a simple algorithm to do this that minimizes edge crossing? (For some graphs, it may be impossible to completely eliminate edge crossing.) A picture says a thousand words, so is there an algorithm that would suggest: instead of: EDIT: As the picture suggests, a vertex's inputs are always on top and outputs are always below, which is another barrier to just pasting in an existing layout algorithm.

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• What kinds of problems are most likely to occur? (question rewritten)

  - by ChrisC

  If I wrote 1) a C# SQL db app (a simple program consisting of a gui over some forms with logic for interfacing with the sql db) 2) for home use, that doesn't do any network communication 3) that uses a simple, reliable, and appropriate sql db 4) whose gui is properly separated from the logic 5) that has complete and dependable input data validation 6) that has been completely tested so that 100% of logic bugs were eliminated ... and then if the program was installed and run by random users on their random Windows computers Q1) What types of technical (non-procedural) problems and support situations are most likely to occur, and how likely are they? Q2) Are there more/other things I could do in the first place to prevent those problems and also minimize the amount of user support required? I know some answers will apply to my specific platforms (C#, SQL, Windows, etc) and some won't. Please be as specific as is possible. Mitch Wheat gave me some very valuable advice below, but I'm now offering the bounty because I am hoping to get a better picture of the kinds of things that I'm most reasonably likely to encounter. Thanks.

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• Function parameters evaluation order: is undefined behaviour if we pass reference?

  - by bolov

  This is undefined behaviour: void feedMeValue(int x, int a) { cout << x << " " << a << endl; } int main() { int a = 2; int &ra = a; feedMeValue(ra = 3, a); return 0; } because depending on what parameter gets evaluated first we could call (3, 2) or (3, 3). However this: void feedMeReference(int x, int const &ref) { cout << x << " " << ref << endl; } int main() { int a = 2; int &ra = a; feedMeReference(ra = 3, a); return 0; } will always output 3 3 since the second parameter is a reference and all parameters have been evaluated before the function call, so even if the second parameter is evaluated before of after ra = 3, the function received a reference to a wich will have a value of 2 or 3 at the time of the evaluation, but will always have the value 3 at the time of the function call. Is the second example UB? It is important to know because the compiler is free to do anything if he detects undefined behaviour, even if I know it would always yield the same results. *Note: I think that feedMeReference(a = 3, a) is the exact same situation as feedMeReference(ra = 3, a). However it seems not everybody agrees, in the addition to having 2 completely different answers.

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• How to identify ideas and concepts in a given text

  - by Nick

  I'm working on a project at the moment where it would be really useful to be able to detect when a certain topic/idea is mentioned in a body of text. For instance, if the text contained: Maybe if you tell me a little more about who Mr Balzac is, that would help. It would also be useful if I could have a description of his appearance, or even better a photograph? It'd be great to be able to detect that the person has asked for a photograph of Mr Balzac. I could take a really naïve approach and just look for the word "photo" or "photograph", but this would obviously be no good if they wrote something like: Please, never send me a photo of Mr Balzac. Does anyone know where to start with this? Is it even possible? I've looked into things like nltk, but I've yet to find an example of someone doing something similar and am still not entirely sure what this kind of analysis is called. Any help that can get me off the ground would be great. Thanks!

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• Fast rectangle to rectangle intersection

  - by Jeremy Rudd

  What's a fast way to test if 2 rectangles are intersecting? A search on the internet came up with this one-liner (WOOT!), but I don't understand how to write it in Javascript, it seems to be written in an ancient form of C++. struct { LONG left; LONG top; LONG right; LONG bottom; } RECT; bool IntersectRect(const RECT * r1, const RECT * r2) { return ! ( r2->left > r1->right || r2->right left || r2->top > r1->bottom || r2->bottom top ); }

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• Code Golf: Spider webs

  - by LiraNuna

  The challenge The shortest code by character count to output a spider web with rings equal to user's input. A spider web is started by reconstructing the center ring: \_|_/ _/ \_ \___/ / | \ Then adding rings equal to the amount entered by the user. A ring is another level of a "spider circles" made from \ / | and _, and wraps the center circle. Input is always guaranteed to be a single positive integer. Test cases Input 1 Output \__|__/ /\_|_/\ _/_/ \_\_ \ \___/ / \/_|_\/ / | \ Input 4 Output \_____|_____/ /\____|____/\ / /\___|___/\ \ / / /\__|__/\ \ \ / / / /\_|_/\ \ \ \ _/_/_/_/_/ \_\_\_\_\_ \ \ \ \ \___/ / / / / \ \ \ \/_|_\/ / / / \ \ \/__|__\/ / / \ \/___|___\/ / \/____|____\/ / | \ Input: 7 Output: \________|________/ /\_______|_______/\ / /\______|______/\ \ / / /\_____|_____/\ \ \ / / / /\____|____/\ \ \ \ / / / / /\___|___/\ \ \ \ \ / / / / / /\__|__/\ \ \ \ \ \ / / / / / / /\_|_/\ \ \ \ \ \ \ _/_/_/_/_/_/_/_/ \_\_\_\_\_\_\_\_ \ \ \ \ \ \ \ \___/ / / / / / / / \ \ \ \ \ \ \/_|_\/ / / / / / / \ \ \ \ \ \/__|__\/ / / / / / \ \ \ \ \/___|___\/ / / / / \ \ \ \/____|____\/ / / / \ \ \/_____|_____\/ / / \ \/______|______\/ / \/_______|_______\/ / | \ Code count includes input/output (i.e full program).

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• Using Inch or cm/mm from metric system for americans and canadians?

  - by gamma

  We're developing an international product that displays a ruler to the user. Now in Germany and many other countries its of course common to use the metric system: cm or mm. I'm aware that americans and canadians (and maybe others too) do still use inches, feet and yards. So the question is: will todays americans (and other inch-country-citizens) understand the metric system and take it for granted - or do they still love their inches so much that they'd rather die than use a product with incorrect measurements? ( sorry for being blunt ;) )

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• Humor in code

  - by pfranza

  When you are writing code or naming products, which sources of cultural references are you most likely to draw from? Which reference sources do you think are more likely to be universally understood? For example when findbugs sees that you've implemented equals() without overriding hashCode() it suggest that you implement it by returning 42 (a reference from HHGTTG) Or why we have big endian vs little endian encoding, referencing Gulliver's Travels Not that we should act unprofessionally with our code, but if you going to tell a person that they could only (watch/read/...) one (book/movie/show/...) which one would allow them to 'get' the most jokes?

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• Is there an existing solution to the multithreaded data structure problem?

  - by thr

  I've had the need for a multi-threaded data structure that supports these claims: Allows multiple concurrent readers and writers Is sorted Is easy to reason about Fulfilling multiple readers and one writer is a lot easier, but I really would wan't to allow multiple writers. I've been doing research into this area, and I'm aware of ConcurrentSkipList (by Lea based on work by Fraser and Harris) as it's implemented in Java SE 6. I've also implemented my own version of a concurrent Skip List based on A Provably Correct Scalable Concurrent Skip List by Herlihy, Lev, Luchangco and Shavit. These two implementations are developed by people that are light years smarter then me, but I still (somewhat ashamed, because it is amazing work) have to ask the question if these are the two only viable implementations of a concurrent multi reader/writer data structures available today?

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• Numeric equivalent of an Excel column name

  - by Vivin Paliath

  The challenge The shortest code by character count that will output the numeric equivalent of an Excel column string. For example, the A column is 1, B is 2, so on and so forth. Once you hit Z, the next column becomes AA, then AB and so on. Test cases: A: 1 B: 2 AD: 30 ABC: 731 WTF: 16074 ROFL: 326676 Code count includes input/output (i.e full program).

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• Another word for Business Logic?

  - by herzmeister der welten

  What is another good word for Business Logic? Software might also run in civil service offices or for hobbyists, so I never felt that comfortable with using that term in certain modules and documentation. App Logic is too specific as well, because logic modules might also be used in services.

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• What design pattern do you use the most?

  - by spoon16

  I'm interested in understanding what design patterns people find themselves using often. Hopefully this list will help other recognize common scenarios and the associated design pattern that can be used to solve them. Please describe a common problem you find yourself solving and the design pattern(s) you use to solve it. Links to blogs or documentation describing the pattern are also appreciated. Edit: Please expand on your answers a bit, I would like this to be a useful reference for someone who wants to learn more about design patterns and is curious on what situations a specific design pattern might be used. Nobody has linked to any "more learning" resources.

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• Helper class(es) vs functional inheritance. Best practice

  - by Andrew Florko

  I have commands classes that implement ICommand { Execute } interface. Several commands have duplicate pieces of code. I have several options how to DRY: Create static helper class(es) and move duplicate code there Create commands inheritance with protected helper methods What would you suggest and why? Thank you in advance!

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• C#, weird optimization

  - by Snake

  Hi, I'm trying to read my compiled C# code. this is my code: using(OleDbCommand insertCommand = new OleDbCommand("...", connection)) { // do super stuff } But! We all know that a using gets translated to this: { OleDbCommand insertCommand = new OleDbCommand("...", connection) try { //do super stuff } finally { if(insertCommand != null) ((IDisposable)insertCommand).Dispose(); } } (since OleDbCommand is a reference type). But when I decompile my assembly (compiled with .NET 2.0) I get this in Resharper: try { insertCommand = new OleDbCommand("", connection); Label_0017: try { //do super stuff } finally { Label_0111: if ((insertCommand == null) != null) { goto Label_0122; } insertCommand.Dispose(); Label_0122:; } I'm talking about this line: if ((insertCommand == null) != null). True is not null, it never is, nor is false. So how is my object disposed properly? WTF? Thanks! -Kristof

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• Usage of closures with multiple arguments in swift

  - by Nilzone-

  This question is largely based on this one: Link The main difference being that I want to pass in arguments to the closure as well. Say I have something like this: func someFunctionThatTakesAClosure(completionClosure: (venues: Dictionary<String, AnyObject>, error: NSError) -> ()) { // function body goes here var error: NSError? let responseDictionary: Dictionary<String, AnyObject> = ["test" : "test2"] completionClosure(venues: responseDictionary, error: error!) } No error here. But when I call this function in my main view controller I have tried several ways but all of the result in different errors: venueService.someFunctionThatTakesAClosure(completionClosure(venues: Dictionary<String, AnyObject>, error: NSError){ }) or like this: venueService.someFunctionThatTakesAClosure((venues: Dictionary<String, AnyObject>, error: NSError){ }) or even like this: venueService.someFunctionThatTakesAClosure(completionClosure: (venues: Dictionary<String, AnyObject>, error: NSError) -> (){ }); I'm probably just way tired, but any help would be greatly appreciated!

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• What programming screencasts/podcast resources do you know?

  - by Ricky AH

  Just as the title says, if you know any resource, answer here. Personally I'm more0interested in screencasts more than podcasts, because english is not my mother tonge, so visual clues help a lot: NetBeans TV Screencasts DimeCasts.NET Apple Developer Connection (iTunes) --- Suggested by the community .NET Rocks dnrTV Channel9 MSDN Events and WebCasts Software Engineering DeepFries RailCasts Learnivore! HanselMinutes ThinkCode

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• Socket Sessions For Persistent Connections

  - by Olaseni

  I am developing a socket server where a client will be bound after being authenticated similar to SMPP. Is there support for cookies in this regard? How do you maintain a session for socket client that is "logged in"?

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• why can't a static member be reached through an instance name?

  - by reinier

  say I have: class Test { public static int Hello = 5; } This obviously works: int j = Test.Hello; But why should this not work? Test test = new Test(); int j = test.Hello; The instance could not have a member equally named, so I don't see how this could be ambiguous or unresolvable for a compiler. Anyone any idea why this is?

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• Python script to calculate aded combinations from a dictionary

  - by dayde

  I am trying to write a script that will take a dictionary of items, each containing properties of values from 0 - 10, and add the various elements to select which combination of items achieve the desired totals. I also need the script to do this, using only items that have the same "slot" in common. For example: item_list = { 'item_1': {'slot': 'top', 'prop_a': 2, 'prop_b': 0, 'prop_c': 2, 'prop_d': 1 }, 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 }, 'item_3': {'slot': 'top', 'prop_a': 2, 'prop_b': 5, 'prop_c': 2, 'prop_d':-2 }, 'item_4': {'slot': 'mid', 'prop_a': 5, 'prop_b': 5, 'prop_c':-5, 'prop_d': 0 }, 'item_5': {'slot': 'mid', 'prop_a':10, 'prop_b': 0, 'prop_c':-5, 'prop_d': 0 }, 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 }, 'item_7': {'slot': 'bot', 'prop_a': 1, 'prop_b': 3, 'prop_c':-4, 'prop_d': 4 }, 'item_8': {'slot': 'bot', 'prop_a': 2, 'prop_b': 2, 'prop_c': 0, 'prop_d': 0 }, 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 }, } The script would then need to select which combinations from the "item_list" dict that using 1 item per "slot" that would achieve a desired result when added. For example, if the desired result was: 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0, the script would select 'item_2', 'item_6', and 'item_9', along with any other combination that worked. 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 } 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 } 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 } 'total': 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0 Any ideas how to accomplish this? It does not need to be in python, or even a thorough script, but just an explanation on how to do this in theory would be enough for me. I have tried working out looping through every combination, but that seems to very quickly get our of hand and unmanageable. The actual script will need to do this for about 1,000 items using 20 different "slots", each with 8 properties. Thanks for the help!

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• Is there a way to formerly define a time interval for configuring a process?

  - by gshauger

  Horrible worded question...I know. I'm working on an application that processes data for the previous day. The problem is that I know the customer is going to eventually ask to it for every hour or some other arbitrary time interval. I know that languages such as Java or SQL have masks for defining dates. Well what about a way to define a time interval? Let me ask it this way. If someone asked you to create a configurable piece of software how would you allow the user to specify the time intervals?

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• Collision detection between ball & bricks in brick breaker game

  - by ketu

  How do you detect a collision between ball & bricks in a brick breaker game?

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• Sharing storage between servers

  - by El Yobo

  I have a PHP based web application which is currently only using one webserver but will shortly be scaling up to another. In most regards this is pretty straightforward, but the application also stores a lot of files on the filesystem. It seems that there are many approaches to sharing the files between the two servers, from the very simple to the reasonably complex. These are the options that I'm aware of Simple network storage NFS SMB/CIFS Clustered filesystems Lustre GFS/GFS2 GlusterFS Hadoop DFS MogileFS What I want is for a file uploaded via one webserver be immediately available if accessed through the other. The data is extremely important and absolutely cannot be lost, so whatever is implemented needs to a) never lose data and b) have very high availability (as good as, or better, than a local filesystem). It seems like the clustered filesystems will also provide faster data access than local storage (for large files) but that isn't of vita importance at the moment. What would you recommend? Do you have any suggestions to add or anything specifically to look out for with the above options? Any suggestions on how to manage backup of data on the clustered filesystems?

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• Code Golf: Rotating Maze

  - by trinithis

  Code Golf: Rotating Maze Make a program that takes in a file consisting of a maze. The maze has walls given by '#'. The maze must include a single ball, given by a 'o' and any number of holes given by a '@'. The maze file can either be entered via command line or read in as a line through standard input. Please specify which in your solution. Your program then does the following: 1: If the ball is not directly above a wall, drop it down to the nearest wall. 2: If the ball passes through a hole during step 1, remove the ball. 3: Display the maze. 4: If there is no ball in the maze, exit. 5: Read a line from the standard input. Given a 1, rotate the maze counterclockwise. Given a 2, rotate the maze clockwise. Rotations are done by 90 degrees. It is up to you to decide if extraneous whitespace is allowed. If the user enters other inputs, repeat this step. 6: Goto step 1. You may assume all input mazes are closed. Note, a hole effectively acts as a wall in this regard. You may assume all input mazes have no extraneous whitespace. The shortest source code by character count wins. Example mazes: ###### #o @# ###### ########### #o # # ####### # ###@ # ######### ########################### # # # # @ # # # # ## # # ####o#### # # # # # # ######### # @ ######################

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• Method of transforming 3D vectors with a matrix

  - by Drew Noakes

  I've been doing some reading on transforming Vector3 with matrices, and am tossing up digging deeper into the math and coding this myself versus using existing code. For whatever reason my school curriculum never included matrices, so I'm filling a gap in my knowledge. Thankfully I only need a few simple things, I think. Context is that I'm programming a robot for the RoboCup 3D league. I'm coding it in C# but it'll have to run on Mono. Ideally I wouldn't use any existing graphics libraries for this (WinForms/WPF/XNA) as all I really need is a neat subset of matrix transformations. Specifically, I need translation and x/y/z rotations, and a way of combining multiple transformations into a single matrix. This will then be applied to my own Vector3 type to produce the transformed Vector3. I've read different advice about this. For example, some model the transformation with a 4x3 matrix, others with a 4x4 matrix. Also, some examples show that you need a forth value for the vector's matrix of 1. What happens to this value when it's included in the output? [1 0 0 0] [x y z 1] * [0 1 0 0] = [a b c d] [0 0 1 0] [2 4 6 1] The parts I'm missing are: What sizes my matrices should be Compositing transformations by multiplying the transformation matrices together Transforming 3D vectors with the resulting matrix As I mostly just want to get this running, any psuedo-code would be great. Information about what matrix values perform what transformations is quite clearly defined on many pages, so need not be discussed here unless you're very keen :)

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• English dictionary as txt or xml file with support of synonyms

  - by Simon

  Can someone point me to where I can download English dictionary as a txt or xml file. I am building a simple app for myself and looking for something what I could start using immediately without learning complex API. Support for synonyms would be great, that is it should be easier to retrieve all the synonyms for particular word. It would be absolutely fantastic if dictionary would be listing British and American spelling of the words where they are differ. Even if it would be small dictionary (few 000's words) that's ok, I only need it for small project. I even would be willing to buy one if the price is reasonable, and dictionary is easy to use - simple xml wold be great. Any directions please.

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