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• iteration on numbers with no 2 same digits

  - by rahmivolkan

  I dont know if it is asked (I couldn't find any). I want to iterate on this kind of numbers implemented on array; int a[10]; int i = 0; for( ; i < 10; i++ ) a[i] = i+1; now the array has "1 2 3 4 5 6 7 8 9 10" and I want to get "1 2 3 4 5 6 7 8 10 9" and then "1 2 3 4 5 6 7 9 8 10" "1 2 3 4 5 6 7 9 10 8" . . . . I tried to get an algorithm but I couldn't figure it out. Is there an easy way to implement "next" iterator for this kind of problems? Thanks in advance

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• Bitmap.Save problems

  - by user284026

  Hello, can anyone tell me if you know to be a problem with Bitmap and steganography for WM 6? I am working on a project and i have to hide a digital signature in a bitmap. The algorithm works perfect, as in untill i have the image on the memory the bitmap contains the modified bytes. But after i save the image (Bitmap.Save()) and I reopen the image, than those bytes are lost. When i say lost i mean they are the orriginal bytes from when the picture was taken. Thank you.

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• What's the bug in the following code ?

  - by Johannes

  #include <iostream> #include <algorithm> #include <vector> #include <boost/array.hpp> #include <boost/bind.hpp> int main() { boost::array<int, 4> a = {45, 11, 67, 23}; std::vector<int> v(a.begin(), a.end()); std::vector<int> v2; std::transform(v.begin(), v.end(), v2.begin(), boost::bind(std::multiplies<int>(), _1, 2)); std::copy(v2.begin(), v2.end(), std::ostream_iterator<int>(std::cout, " ")); } When run, this gives a creepy segmentation fault. Please tell me where I'm going wrong.

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• what mysql table structure is better

  - by Sergey

  I have very complicated search algorithm on my site, so i decided to make a table with cache or maybe all possible results. I wanna ask what structure would be better, or maybe not the one of them? (mySQL) 1) word VARCHAR, results TEXT or BLOB where i'll store ids of found objects (for example 6 chars for each id) 2) word VARCHAR, result INT, but words are not unique now i think i'll have about 200 000 rows in 1) with 1000-10000 ids each row or 200 000 000+ rows in 2) First way takes more storage memory but i think it would be much faster to find 1 unique row among 200 000, than 1000 rows among 200 mln non unique rows i think about index on word column and no sphinx. So that do YOU think? p.s. as always, sorry for my english if it's not very good.

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• Beginner C: error: control reaches end of non-void function?

  - by Ting

  I'm trying to make a greedy algorithm and I get this error: greedy2.c:27:1: error: control reaches end of non-void function [-Werror,-Wreturn-type] } ^ 1 error generated. with this code: int man(int argc, char* argv[]) { float amount; do { printf("Input dollar amount owed:\n"); amount = GetFloat(); } while (amount <= 0); int coins = 0; while (amount >= 0.25); { amount = amount - 0.25; coins++; } printf("Number of coins to use: %d\n", coins); } What is wrong with my curly braces, and how do I fix it?

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• Random numbers from binomial distribution

  - by Sarah

  I need to generate quickly lots of random numbers from binomial distributions for dramatically different trial sizes (most, however, will be small). I was hoping not to have to code an algorithm by hand (see, e.g., this related discussion from November), because I'm a novice programmer and don't like reinventing wheels. It appears Boost does not supply a generator for binomially distributed variates, but TR1 and GSL do. Is there a good reason to choose one over the other, or is it better that I write something customized to my situation? I don't know if this makes sense, but I'll alternate between generating numbers from uniform distributions and binomial distributions throughout the program, and I'd like for them to share the same seed and to minimize overhead. I'd love some advice or examples for what I should be considering.

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• Automatic people counting + twittering.

  - by c2h2

  Want to develop a system accurately counting people that go through a normal 1-2m wide door. and twitter whenever people goes in or out and tells how many people remain inside. Now, Twitter part is easy, but people counting is difficult. There is some semi existing counting solution, but they do not quite fit my needs. My idea/algorithm: Should I get some infra-red camera mounting on top of my door and constantly monitoring, and divide the camera image into several grid and calculating they entering and gone? can you give me some suggestion and starting point?

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• How are managed the sequences by JPA and Hibernate?

  - by romaintaz

  Hi all, I am using Hibernate in my project, and many of my entities use a sequence for their technical keys. For example: @Entity @Table(name = "T_MYENTITY") @SequenceGenerator(name = "S_MYENTITY", sequenceName = "S_MYENTITY") public class MyEntity { @Id @GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "S_MYENTITY") @Column(name = "MY_ENTITY_ID") private Long entityId; ... } I have two questions about the ID generated by Hibernate when a new object of this class is persisted: Why SequenceGenerator (from javax.persistence) has a default value of allocationSize set to 50 instead of 1? What are the interests of that? What is the default algorithm used by Hibernate to calculate the generated ID? It seems that Hibernate uses the value returned by the sequence hosted by my Oracle database, but then modify it before assigning it to my entity...

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• How to program a connection pool?

  - by the_drow

  Is there a known algorithm for implementing a connection pool? If not what are the known algorithms and what are their trade-offs? What design patterns are common when designing and programming a connection pool? Are there any code examples implement a connection pool using boost.asio? Is it a good idea to use a connection pool for presisting connections (not http)? How is threading related to connection pooling? When do you need a new thread?

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• Update NSView in function of events

  - by Forchita

  Hi everyone! I have a main view (subclass of NSView) and as i'm new to cocoa, i'd like to know how to update the view in function of events. I know there are many methods that take events such as -(void)mouseMoved:(NSEvent*)event or - (void)mouseClicked:(NSEvent*)event My algorithm to determine what to do is ready. I want to know where I should update the main view: is it in the -(void)mouseMoved:(NSEvent*)event or in the - (void)drawRect:(NSRect)dirtyRect. And if it is in drawRect, then how should i pass the information to it? Thanks in advance!

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• How can you deflect a direction/magnitude vector based on a direction/magnitude vector and a collided triangle?

  - by JeanOTF

  So, I have a Triangle-AABB collision algorithm and I have it returning the triangle that the AABB collided with. I was hoping with the 3 vectors of the triangle and the direction/magnitude of the movement would let me determine a deflected vector so that when you run against the wall at an angle you move slower, depending on the angle of collision, but along side the wall. This would remove the sticky collision problem with only moving when there is not a collision. Any suggestions or references would be greatly appreciated! Thanks.

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• Any chances to imitate times() Ruby method in C#?

  - by Alexander Prokofyev

  Every time I need to do something N times inside an algorithm using C# I write this code for (int i = 0; i < N; i++) { ... } Studying Ruby I have learned about method times() which can be used with the same semantics like this N.times do ... end Code fragment in C# looks more complex and we should declare useless variable i. I tried to write extension method which returns IEnumerable, but I am not satisfied with the result because again I have to declare a cycle variable i. public static class IntExtender { public static IEnumerable Times(this int times) { for (int i = 0; i < times; i++) yield return true; } } ... foreach (var i in 5.Times()) { ... } Is it possible using some new C# 3.0 language features to make N times cycle more elegant?

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• Use C function in C++ program; "multiply-defined" error

  - by eom

  I am trying to use this code for the Porter stemming algorithm in a C++ program I've already written. I followed the instructions near the end of the file for using the code as a separate module. I created a file, stem.c, that ends after the definition and has extern int stem(char * p, int i, int j) ... It worked fine in Xcode but it does not work for me on Unix with gcc 4.1.1--strange because usually I have no problem moving between the two. I get the error ld: fatal: symbol `stem(char*, int, int)' is multiply-defined: (file /var/tmp//ccrWWlnb.o type=FUNC; file /var/tmp//cc6rUXka.o type=FUNC); ld: fatal: File processing errors. No output written to cluster I've looked online and it seems like there are many things I could have wrong, but I'm not sure what combination of a header file, extern "C", etc. would work.

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• Windows Server 2008 Antivirus Software with an API

  - by Dave Jellison

  I'm looking for an Antivirus package that is compliant with Windows Server 2008. That's not the hard part. What I need is an API layer on the Antivirus that i can call from managed .net code. For example: I am developing an Asp.Net (C#) website that allows users to upload files to the web server which the web site resides on. We have full control of the server so there are no security/rights issues on the server. I need to be able to run the antivirus algorithm on the newly uploaded files without (hopefully) shelling out to a command-ilne version of the software. Does anyone know of such a package?

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• Sorting 1000-2000 elements with many cache misses

  - by Soylent Graham

  I have an array of 1000-2000 elements which are pointers to objects. I want to keep my array sorted and obviously I want to do this as quick as possible. They are sorted by a member and not allocated contiguously so assume a cache miss whenever I access the sort-by member. Currently I'm sorting on-demand rather than on-add, but because of the cache misses and [presumably] non-inlining of the member access the inner loop of my quick sort is slow. I'm doing tests and trying things now, (and see what the actual bottleneck is) but can anyone recommend a good alternative to speeding this up? Should I do an insert-sort instead of quicksorting on-demand, or should I try and change my model to make the elements contigious and reduce cache misses? OR, is there a sort algorithm I've not come accross which is good for data that is going to cache miss?

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• Any tips of how to handle hierarchial trees in relational model?

  - by George

  Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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• Quick-sort doesn't work with middle pivot element

  - by Bobby

  I am trying to sort an array of elements using quick-sort algorithm.But I am not sure where am I going wrong.I choose the middle element as pivot every time and then I am checking the conditions.Here is my code below. void quicksort(int *temp,int p,int r) { if(r>p+1) { int mid=(p+r)/2; int piv=temp[mid]; int left=p+1; int right=r; while(left < right) { if(temp[left]<=piv) left++; else swap(&temp[left],&temp[--right]); } swap(&temp[--left],&temp[p]); quicksort(temp,p,left); quicksort(temp,right,r); } }

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• Is there a class like a Dictionary without a Value template? Is HashSet<T> the correct answer?

  - by myotherme

  I have 3 tables: Foos, Bars and FooBarConfirmations I want to have a in-memory list of FooBarConfirmations by their hash: FooID BarID Hash 1 1 1_1 2 1 2_1 1 2 1_2 2 2 2_2 What would be the best Class to use to store this type of structure in-memory, so that I can quickly check to see if a combination exists like so: list.Contains("1_2"); I can do this with Dictionary<string,anything>, but it "feels" wrong. HashSet looks like the right tool for the job, but does it use some form of hashing algorithm in the background to do the lookups efficiently?

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• Deleting Part of An Array in Java to Free Memory on Heap

  - by kate

  I am implementing a dynamic programming algorithm for the knapsack problem in Java. I declare the array and then initialize its size to be [number of objects][capacity of knapsack]. When my number of objects or my capacity gets too large, I get a memory error because I run out of space on the heap. My questions is: If I delete rows from my double array as I go along, will Java free the memory as I delete? Or does Java reserve that memory space for the size of the array I originally created? If it's the latter, is there a way to manually free the memory in Java? Thanks for your Help!

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• Overhead of serving pages - JSPs vs. PHP vs. ASPXs vs. C

  - by John Shedletsky

  I am interested in writing my own internet ad server. I want to serve billions of impressions with as little hardware possible. Which server-side technologies are best suited for this task? I am asking about the relative overhead of serving my ad pages as either pages rendered by PHP, or Java, or .net, or coding Http responses directly in C and writing some multi-socket IO monster to serve requests (I assume this one wins, but if my assumption is wrong, that would actually be most interesting). Obviously all the most efficient optimizations are done at the algorithm level, but I figure there has got to be some speed differences at the end of the day that makes one method of serving ads better than another. How much overhead does something like apache or IIS introduce? There's got to be a ton of extra junk in there I don't need. At some point I guess this is more a question of which platform/language combo is best suited - please excuse the in-adroitly posed question, hopefully you understand what I am trying to get at.

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• aspx page gives viewstate error

  - by Priya10

  Hi, I have a simple aspx page with one grid view. When deployed on server, and accessed through that machine, it works fine. However, when connected through load balancer, we get this error ( when click on any button). The page however refreshes when pressed F5. Validation of viewstate MAC failed. If this application is hosted by a Web Farm or cluster, ensure that <machineKey> configuration specifies the same validationKey and validation algorithm. AutoGenerate cannot be used in a cluster. Any idea what is happening here???

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• Disposing a Bitmap through its Finalizer

  - by devoured elysium

  I have a complex program in which I have to first create, then use wrappers around bitmaps and send them across a lot of different classes. The problem in the end is deciding which classes should dispose the bitmaps. Most of the time the end classes don't know if they can indeed dispose the bitmap as the same bitmap can be used in several places. Also, I can't just copy the bitmaps because this is a kind of resource intensive algorithm and doing it would be dead slow. I looked up on reflector for Image/Bitmap's implementations and they seem to use the Dispose Pattern. So, even if I don't call Dispose(), the CLR will eventually call it some other time. Is it too bad if I just let the bitmaps be as they are, and let the finalizer take care of them?

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• Architecture for analysing search result impressions/clicks to improve future searches

  - by Hais

  We have a large database of items (10m+) stored in MySQL and intend to implement search on metadata on these items, taking advantage of something like Sphinx. The dataset will be changing slightly on a daily basis so Sphinx will be re-indexing daily. However we want the algorithm to self-learn and improve search results by analysing impression and click data so that we provide better results for our customers on that search term, and possibly other similar search terms too. I've been reading up on Hadoop and it seems like it has the potential to crunch all this data, although I'm still unsure how to approach it. Amazon has tutorials for compiling impression vs click data using MapReduce but I can't see how to get this data in a useable format. My idea is that when a search term comes in I query Sphinx to get all the matching items from the dataset, then query the analytics (compiled on an hourly basis or similar) so that we know the most popular items for that search term, then cache the final results using something like Memcached, Membase or similar. Am I along the right lines here?

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• Counting variables per observation per month in Sas.

  - by John

  Hey guys, a quick question, I have data of the following sort: Ticker _ Date _ Fem Analyst (dummy 1 if true) AA _ 04/2001 _ 1 AA _ 04/2001 _ 1 AA _ 04/2001 _ 1 AA _ 05/2002 _ 1 AA _ 05/2002 _ 1 AA _ 07/2002 _ 0 AA _ 04/2003 _ 1 and so on.. What I want to receive is the following: Ticker _ Date _ Number of fem analyst AA _ 04/2001 _ 3 AA _ 05/2002 _ 2 AA _ 07/2002 _ 0 AA _ 04/2003 _ 1 So an easy counting algorithm that allows me to count for the number of analysts per company per month (the date is in 01/04/2002 format but I also have a month count variable which can be used too) Any ideas?

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• Merging and splitting overlapping rectangles to produce non-overlapping ones

  - by uj

  I am looking for an algorithm as follows: Given a set of possibly overlapping rectangles (All of which are "not rotated", can be uniformly represented as (left,top,right,bottom) tuplets, etc...), it returns a minimal set of (non-rotated) non-overlapping rectangles, that occupy the same area. It seems simple enough at first glance, but prooves to be tricky (at least to be done efficiently). Are there some known methods for this/ideas/pointers? Methods for not necessarily minimal, but heuristicly small, sets, are interesting as well, so are methods that produce any valid output set at all.

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