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• How to detect if breaking an edge will make a graph disjoint?

  - by the_graph_guy

  I have a graph that starts off with a single, root node. Nodes are added one by one to the graph. At node creation time, they have to be linked either to the root node, or to another node, by a single edge. Edges can also be created and deleted (one by one, between any two nodes). Nodes can be deleted one at a time. Node and edge creation, deletion operations can happen in any arbitrary order. OK, so here's my question: When an edge is deleted, is it possible do determine, in constant time (i.e. with an O(1) algorithm), if doing this will divide the graph into two disjoint subgraphs? If it will, then which side of the edge will the root node belong? I'm willing to maintain, within reasonable limits, any additional data structure that can facilitate the derivation of this information. Maybe it is not possible to do it in O(1), if so any pointers to literature will be appreciated.

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• Which parallel sorting algorithm has the best average case performance?

  - by Craig P. Motlin

  Sorting takes O(n log n) in the serial case. If we have O(n) processors we would hope for a linear speedup. O(log n) parallel algorithms exist but they have a very high constant. They also aren't applicable on commodity hardware which doesn't have anywhere near O(n) processors. With p processors, reasonable algorithms should take O(n/p log n/p) time. In the serial case, quick sort has the best runtime complexity on average. A parallel quick sort algorithm is easy to implement (see here and here). However it doesn't perform well since the very first step is to partition the whole collection on a single core. I have found information on many parallel sort algorithms but so far I have not seen anything pointing to a clear winner. I'm looking to sort lists of 1 million to 100 million elements in a JVM language running on 8 to 32 cores.

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• iPhone Accelerometer Values

  - by Mike

  My question is about the iPhone accelerometer. Does the accelerometer measure acceleration or movement of the iPhone? What I mean is if I hold the iPhone and go from 0mph to 60mph, I would expect the measure of acceleration to increase in value from 0 to 60, but once I reach 60, I expect the value to return to 0 since I am "no longer accelerating" but am moving at a constant speed. Now if the accelerometer measure motion, I would expect it to register 0 to 60 and continue to provide a change in value as I move forward at 60mph. Sorry, I looked at a few books, programmed some code (values seemed to small to give a recognizable result over short distances or speeds), and a lot of web searches, and I am trying to get an answer to this question. Thanx!

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• How to research unmanaged memory leaks in .NET?

  - by Brandon

  I have a WCF service running over MSMQ. Memory gradually increases over time, indicating that there is some sort of memory leak. I ran the service locally and monitored some counters using PerfMon. Total CLR memory managed heap bytes remains relatively constant, while the process' private bytes increases over time. This leads me to believe that there is some sort of unmanaged memory leak. Assuming that unmanaged memory leak is the issue, how do I address the issue? Are there any tools I could use to give me hints as to what is causing the unmanaged memory leak? Also, all my service is doing is reading from the transactional queue and writing to a database, all as part of a DTC transaction (handled under the hood by requiring a transaction on the service contract). I am not doing anything explicitly with COM or DllImports. Thanks in advance!

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• C++ static virtual members?

  - by cvb

  Is it possible in C++ to have a member function that is both static and virtual? Apperantly, there isn't a straight-forward way to do it (static virtual member(); is a complie error), but at least a way to acheive the same effect? I.E: struct Object { struct TypeInformation; static virtual const TypeInformation &GetTypeInformation() const; }; struct SomeObject : public Object { static virtual const TypeInformation &GetTypeInformation() const; }; It makes sence to use GetTypeInformation() both on an instance (object->GetTypeInformation()) and on a class (SomeObject::GetTypeInformation()), which can be useful for comparsions and vital for templates. The only ways I can think of involves writing two functions / a function and a constant, per class, or use macros. Any other solutions?

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• What is the cost of memory access?

  - by Jurily

  We like to think that a memory access is fast and constant, but on modern architectures/OSes, that's not necessarily true. Consider the following C code: int i = 34; int *p = &i; // do something that may or may not involve i and p {...} // 3 days later: *p = 643; What is the estimated cost of this last assignment in CPU instructions, if i is in L1 cache, i is in L2 cache, i is in L3 cache, i is in RAM proper, i is paged out to an SSD disk, i is paged out to a traditional disk? Where else can i be? Of course the numbers are not absolute, but I'm only interested in orders of magnitude. I tried searching the webs, but Google did not bless me this time.

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• php script to generate checksum from md5

  - by sumit

  In order to calculate the checksum i need following things. these parameters are concatenated in a constant (no spaces) string made up of the values of the following parameters in the exact order listed below: o Secret Key o Merchant id o Currency o Total amount o Item list (item_name_1, Item_amount_1, item_quantity_1 to item_name_N, Item_amount_N, item_quantity_N) o Timestamp e.g In that case the string befor hash will be: pLAZdfhdfdNh57583USD69.99Tier2 item69.9912010-06-14.14:34:33 And using the MD5 hash function the result is: ghvsaf764t3w784tbjkegbjhdbgf i want to know how can i create a php script that will call md5 hash function with the inputs given above and based on that it will generate the hash function value that will be the checksum value for my coding..

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• Understanding c++ block of code

  - by kotoko

  I was given a c++ main and have to code it so it works. I am having some trouble understanding the code as I am a bit new to cpp. Here is the code int main(int argc, char *argv[]) { Class::setAtribute("string"); Class(Class::CONSTANT) << "starting up..."; } Some questions: How can the first line work with no variables? Is it static? The second line is really strange for me, what I can make out is a Constructor that takes in a class constante and then prints it out somehow? If someone could explain me this bit of code it would be great! Thanks in advance.

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• a newbie gcc compiler and c language question

  - by dydx

  Hi, when I'm trying to compile my c program it gives me this error warning: integer constant is too large for 'long' type which refers to these lines int barcode, a, b, c; scanf("%d", &barcode); a = barcode / 1000000000000; b = barcode / 100000000000 % 10; c = barcode / 10000000000 % 10; and the rest is fine. I know I'm not supposed to use int for such a large number, any suggestions on what I should use? if I replace int with double what should the '%d' part be replaced with then?

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• Calculating the angle between two points

  - by kingrichard2005

  I'm currently developing a simple 2D game for Android. I have a stationary object that's situated in the center of the screen and I'm trying to get that object to rotate and point to the area on the screen that the user touches. I have the constant coordinates that represent the center of the screen and I can get the coordinates of the point that the user taps on. I'm using the formula outlined in this forum: How to get angle between two points? -It says as follows "If you want the the angle between the line defined by these two points and the horizontal axis: double angle = atan2(y2 - y1, x2 - x1) * 180 / PI;". -I implemented this, but I think the fact the I'm working in screen coordinates is causing a miscalculation, since the Y-coordinate is reversed. I'm not sure if this is the right way to go about it, any other thoughts or suggestions are appreciated.

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• Large amount of constants in Java

  - by Lars D

  I need to include about 1 MByte of data in a Java application, for very fast and easy access in the rest of the source code. My main background is not Java, so my initial idea was to convert the data directly to Java source code, defining 1MByte of constant arrays, classes (instead of C++ struct) etc., something like this: public final/immutable/const MyClass MyList[] = { { 23012, 22, "Hamburger"} , { 28375, 123, "Kieler"} }; However, it seems that Java does not support such constructs. Is this correct? If yes, what is the best solution to this problem?

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• modifying constants in objective c during run time

  - by moshikafya

  I am trying to solve the following problem. I have the following constants in my header file: #define PREFS_MY_CONSTANT_1 @"bla1" #define PREFS_MY_CONSTANT_2 @"bla2" #define PREFS_MY_CONSTANT_3 @"bla3" ... In one of my functions, I'd like to print to the UIbutton one of those strings based on user input, so say the user inputs '1', i would show bla1. Instead of creating a huge switch (i have 100 of those), I am looking for a way to combine the constant with the variable holding the user input, so something like that ideally: NSInteger input; [button setTitle:PREFS_MY_CONSTANT_{$input} forState: UIControlStateNormal]; Is something like that possible? what would be the best way to solve this?

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• Is there a way to create my own "push pins" for a image without using Google Maps API?

  - by Charlie

  I am interested in working with friends via the internet on a fantasy world map. One of the things I want to do is host an image of the map online and allow us to insert push pins into the image that would then be associated with infoboxes. I don't want to resort to using the Google Map APIs mainly because this is something I want to just share among friends and not publicly. Terms of usage for the APIs state we would need to make the implementation available for everyone. This seems simple enough yet I've no idea how to do this. I looked into image maps, but that requires constant updates to the html markup itself. I just want to insert/delete/edit pushpins and infoboxes on the image and through our site itself. Can someone help me get started?

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• Why operator= returns reference not const reference

  - by outmind

  The original question is related to overloading operator= and I like to share my findings as it was nontrivial for me to find them. I cannot imagine reasonable example to use (a=b) as lvalue. With the help of IRC and google I've found the next article: http://msdn.microsoft.com/en-us/magazine/cc301415.aspx it provides two examples. (a=b)=c f(T& ); f(a=b) but both a bit not good, as first violate associativity and I believe that it is bad practice. The second one give me the same feeling. Could you provide more good examples why it should be non constant?

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• Hide Adsense on localhost

  - by collimarco

  I have a site built in Ruby On Rails which has many ads in different templates and views. It is hard to actualy remove each ad between tests and deployments. I don't know whether Google approves many impressions (even if without clicks) on localhost. How do you deal with this issue? Maybe it is a good solution to set a variable/constant available everywere to enable/disable ads easily. Do you think it is a good solution? If so, how do I declare a global variable for views?

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• How do you make long SQL invoked from other code readable?

  - by Artem

  This is a very open question, but I think it can be very beneficial for SQL readability. So you have a Java program, and you are trying to call a monster SQL statement from it, with many subqueries and joins. The starting point for my question is a string constant like this: static string MONSTER_STATEMENT = "SELECT " + " fields" + "WHERE "+ " fieldA = (SELECT a FROM TableC) " + "AND fieldB IN (%s)" + "AND fieldC = %d " + "FROM " " tableA INNER JOIN tableB ON ..."; It later gets filled using String.format and executed. What are you tricks for making this kind of stuff readable? Do you separate your inner joins. Do you indent the SQL itself inside the string? Where do you put the comments? Please share all of the tricks in your arsenal.

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• Arrange 0's & 1's in a array

  - by Ganesh M

  This is one of an interview question which I had recently. I would like to know others perception of approach for this problem. Question: You are given a structure which holds an employee details with two elements as int Deptartment and string Name. struct Employee { string Name; int Dept; } You are given details of N Employees among which there are N/2 employees Dept are 0's and N/2 employees dept are 1's arranged in some random order. You need to sort the employee details based on their Dept value and it should be stable i.e., the order of 1s and 0s in the original record should be maintained. For example, given the following sample data: Name Dept X1 0 X2 1 X3 0 X4 1 X5 0 after sorting the result should be: Name Dept X2 1 X4 1 X1 0 X3 0 X5 0 The algorithm should be stable and the complexity should be o(N), with constant space for additional variables (which means sorting should be done in-place).

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• Haskell: foldl' accumulator parameter

  - by Clinton

  I've been asking a few questions about strictness, but I think I've missed the mark before. Hopefully this is more precise. Lets say we have: n = 1000000 f z = foldl' (\(x1, x2) y -> (x1 + y, y - x2)) z [1..n] Without changing f, what should I set z = ... So that f z does not overflow the stack? (i.e. runs in constant space regardless of the size of n) Its okay if the answer requires GHC extensions. My first thought is to define: g (a1, a2) = (!a1, !a2) and then z = g (0, 0) But I don't think g is valid Haskell.

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• How are files (especially audio files) organized internally?

  - by mystify

  I try to grok that: Apple is talking about "packets" in audio files, and there is a fancy function called AudioFileReadPackets which takes a lot of arguments. One of them specifies the "start packet", and another one the number of packets which you want to read. So I imagine an audio file to look like this, internally: It's made up of a lot of packets. If it's an audio file which has an variable bit rate format, then every packet may have a different size. If the file has an constant bit rate format, then every packet is the same size. So an audio file is like a truck full of boxes, and every box contains some interesting stuff. Is that correct? Does it apply to any kind of file? Is this how files actually look like?

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• Can we avoid multiple if''s?

  - by Newbie

  I tried my level best to write an improved version but failed. inFiles.ToList().ForEach(i => { filePath = inFolder + "\\" + i.Value; if (i.Key.Equals(replacementFile)) { replacementCollection = GetReplacementDataFromFile(filePath); } else if (i.Key.Equals(standardizationFile)) { standardizationCollection = GetStandardizationDataFromFile(filePath); } }); The problem is that I cannot use a switch case over here because the comparison variables are not constant. Kindly help to improve this code. I am using C#(3.0). Thanks

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• Which is the better way to avoid magic string keys? Using string const keys in a class or using enumeration?

  - by user596314

  My idea is to avoid magic string keys in my Asp.Net MVC application. To do so, I want to create string constant keys to be shared in the application. For example, I can write TempData[MyClass.Message] or TempData[MyEnum.Message.ToString()] instead of TempData["Message"]. public class MyClass { public const string Message = "Message"; } and public enum MyEnum { Message, Others } My questions are: Which is the better way to avoid magic string keys? Using string const keys in a class or using enumeration together with ToString()?

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• Simple Java math operations

  - by user1730056

  I'm making a BMI calculator that doesn't seem to be working. The math operations work if i just do something like w/h, but once i had the brackets, it returns an error. If i change the variables w and h and use a constant number, the operation works. Another problem is that although i'm making result a double, it seems to be rounding to the nearest int. Could someone tell me what I'm doing wrong here? public class ass10 { public static void main(String[] args) { bmi(223,100); } public static bmi(int w, int h){ double result; result = (w/(h*h))*703 System.out.println(result) } }

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• C++ open() fails for no apparant reason

  - by jondoe

  The following code: char filename[64]; ifstream input; cout << "Please enter the filename: " << endl; cin >> filename; input.open(filename); if (!input.is_open()) { cout << "Opening file " << filename << " failed." << endl; exit(1); } fails, it enters the if() and exits. What could possibly be the cause for this? I'm using Microsoft Visual C++. When I hardcoded the filename as a constant it instead ended up garbled: http://pici.se/pictures/CNQEnwhgo.png Suggestions?

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• Compare two integer arrays with same length

  - by meta

  [Description] Given two integer arrays with the same length. Design an algorithm which can judge whether they're the same, the definition of "same" is that, if these two arrays are in sorted order, the elements in corresponding position should be the same. [Example] <1 2 3 4> = <3 1 2 4> <1 2 3 4> != <3 4 1 1> [Limitation] The algorithm should require constant extra space, and O(n) running time.

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• how to use constants in SQL CREATE TABLE?

  - by kchiu

  Hi, I have 3 SQL tables, defined as follows: CREATE TABLE organs( abbreviation VARCHAR(16), -- ... other stuff ); CREATE TABLE blocks( abbreviation VARCHAR(16), -- ... other stuff ); CREATE TABLE slides( title VARCHAR(16), -- ... other stuff ); The 3 fields above all use VARCHAR(16) because they're related and have the same length restriction. Is there a (preferably portable) way to put '16' into a constant / variable and reference that instead in CREATE TABLE? eg. something like this would be nice: CREATE TABLE slides( title VARCHAR(MAX_TITLE_LENGTH), -- ... other stuff ); I'm using PostgreSQL 8.4. thanks a lot, and Happy New Year! cheers.

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