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  • Sorting a list of numbers with modified cost

    - by David
    First, this was one of the four problems we had to solve in a project last year and I couldn’t find a suitable algorithm so we handle in a brute force solution. Problem: The numbers are in a list that is not sorted and supports only one type of operation. The operation is defined as follows: Given a position i and a position j the operation moves the number at position i to position j without altering the relative order of the other numbers. If i j, the positions of the numbers between positions j and i - 1 increment by 1, otherwise if i < j the positions of the numbers between positions i+1 and j decreases by 1. This operation requires i steps to find a number to move and j steps to locate the position to which you want to move it. Then the number of steps required to move a number of position i to position j is i+j. We need to design an algorithm that given a list of numbers, determine the optimal (in terms of cost) sequence of moves to rearrange the sequence. Attempts: Part of our investigation was around NP-Completeness, we make it a decision problem and try to find a suitable transformation to any of the problems listed in Garey and Johnson’s book: Computers and Intractability with no results. There is also no direct reference (from our point of view) to this kind of variation in Donald E. Knuth’s book: The art of Computer Programing Vol. 3 Sorting and Searching. We also analyzed algorithms to sort linked lists but none of them gives a good idea to find de optimal sequence of movements. Note that the idea is not to find an algorithm that orders the sequence, but one to tell me the optimal sequence of movements in terms of cost that organizes the sequence, you can make a copy and sort it to analyze the final position of the elements if you want, in fact we may assume that the list contains the numbers from 1 to n, so we know where we want to put each number, we are just concerned with minimizing the total cost of the steps. We tested several greedy approaches but all of them failed, divide and conquer sorting algorithms can’t be used because they swap with no cost portions of the list and our dynamic programing approaches had to consider many cases. The brute force recursive algorithm takes all the possible combinations of movements from i to j and then again all the possible moments of the rest of the element’s, at the end it returns the sequence with less total cost that sorted the list, as you can imagine the cost of this algorithm is brutal and makes it impracticable for more than 8 elements. Our observations: n movements is not necessarily cheaper than n+1 movements (unlike swaps in arrays that are O(1)). There are basically two ways of moving one element from position i to j: one is to move it directly and the other is to move other elements around i in a way that it reaches the position j. At most you make n-1 movements (the untouched element reaches its position alone). If it is the optimal sequence of movements then you didn’t move the same element twice.

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  • And now for a complete change of direction from C++ function pointers

    - by David
    I am building a part of a simulator. We are building off of a legacy simulator, but going in different direction, incorporating live bits along side of the simulated bits. The piece I am working on has to, effectively route commands from the central controller to the various bits. In the legacy code, there is a const array populated with an enumerated type. A command comes in, it is looked up in the table, then shipped off to a switch statement keyed by the enumerated type. The type enumeration has a choice VALID_BUT_NOT_SIMULATED, which is effectively a no-op from the point of the sim. I need to turn those no-ops into commands to actual other things [new simulated bits| live bits]. The new stuff and the live stuff have different interfaces than the old stuff [which makes me laugh about the shill job that it took to make it all happen, but that is a topic for a different discussion]. I like the array because it is a very apt description of the live thing this chunk is simulating [latching circuits by row and column]. I thought that I would try to replace the enumerated types in the array with pointers to functions and call them directly. This would be in lieu of the lookup+switch.

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  • mysql select where count = 0

    - by david parloir
    Hi, In my db, I have a "sales" table and a "sales_item". Sometimes, something goes wrong and the sale is recorded but not the sales item's. So I'm trying to get the salesID from my table "sales" that haven't got any rows in the sales_item table. Here's the mysql query I thought would work, but it doesn't: SELECT s.* FROM sales s NATURAL JOIN sales_item si WHERE s.date like '" . ((isset($_GET['date'])) ? $_GET['date'] : date("Y-m-d")) . "%' AND v.sales_id like '" . ((isset($_GET['shop'])) ? $_GET['shop'] : substr($_COOKIE['shop'], 0, 3)) ."%' HAVING count(si.sales_item_id) = 0; Any thoughts?

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  • Multithreading for loop while maintaining order

    - by David
    I started messing around with multithreading for a CPU intensive batch process I'm running. Essentially I'm trying to condense multiple single page tiffs into single PDF documents. This works fine with a foreach loop or standard iteration but can be very slow for several 100 page documents. I tried the following based on a some examples I found to use multithreading and it has significant performance improvements however it obliterates the page order instead of 1,2,3,4 it will be 1,3,4,2,6,5 on what thread completes first. My question is how would I utilize this technique while maintaining the page order and if I can will it negate the performance benefit of the multithreading? Thank you in advance. PdfDocument doc = new PdfDocument(); string mail = textBox1.Text; string[] split = mail.Split(new string[] { Environment.NewLine }, StringSplitOptions.None); int counter = split.Count(); // Source must be array or IList. var source = Enumerable.Range(0, 100000).ToArray(); // Partition the entire source array. var rangePartitioner = Partitioner.Create(0, counter); double[] results = new double[counter]; // Loop over the partitions in parallel. Parallel.ForEach(rangePartitioner, (range, loopState) => { // Loop over each range element without a delegate invocation. for (int i = range.Item1; i < range.Item2; i++) { f_prime = split[i].Replace(" " , ""); PdfPage page = doc.AddPage(); XGraphics gfx = XGraphics.FromPdfPage(page); XImage image = XImage.FromFile(f_prime); double x = 0; gfx.DrawImage(image, x, 0); } });

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  • Trouble with go tour crawler exercise

    - by David Mason
    I'm going through the go tour and I feel like I have a pretty good understanding of the language except for concurrency. On slide 71 there is an exercise that asks the reader to parallelize a web crawler (and to make it not cover repeats but I haven't gotten there yet.) Here is what I have so far: func Crawl(url string, depth int, fetcher Fetcher, ch chan string) { if depth <= 0 { return } body, urls, err := fetcher.Fetch(url) if err != nil { ch <- fmt.Sprintln(err) return } ch <- fmt.Sprintf("found: %s %q\n", url, body) for _, u := range urls { go Crawl(u, depth-1, fetcher, ch) } } func main() { ch := make(chan string, 100) go Crawl("http://golang.org/", 4, fetcher, ch) for i := range ch { fmt.Println(i) } } The issue I have is where to put the close(ch) call. If I put a defer close(ch) somewhere in the Crawl method, then I end up writing to a closed channel in one of the spawned goroutines, since the method will finish execution before the spawned goroutines do. If I omit the call to close(ch), as is shown in my example code, the program deadlocks after all the goroutines finish executing but the main thread is still waiting on the channel in the for loop since the channel was never closed.

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  • SoundManager + FFMPEG causing loud popping sound when streaming MP3s?

    - by David
    Hi there, I built an application that plays both uploaded original mp3 files, and copies that have been converted with FFMPEG. I am finding that in some cases the FFMPEG files have a horrible popping/clicking/screeching sound for a split second at startup (hear below). But when I analyze the file in an audio editor there is nothing there, so it seems to be either the browser or soundManager reacting badly to something in that file. Wondering if there is any way I can fix this either by adjusting FFMPEG settings, soundManager settings, or..... Any suggestions? I've uploaded the offending sound in the link below (before the music starts playing). Thanks for your help! Hear sound

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  • h2 & linux. how to start the database?

    - by David
    sorry im rather new to linux ubuntu. i have an application that i made that runs with tomcat and connects to an h2 database. it all works fine on my windows laptop. im now moving it onto my linux computer to run all the time. but im having trouble with starting the database. i have downloaded h2 from their website. and its sitting on my desktop. the question is. how to start the database. and is their any other commands i need to know to run and operate it. thankyous

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  • Flexible string handling in Visual Studio 2008 C++

    - by David
    I'm slowly starting to get the hang of the _T stuff in Visual Studio 2008 c++, but a few things still elude me. I can see the benefit of the flexibility, but if I can't get the basics soon, I think I'll go back to the standard way of doing this - much less confusing. The idea with the code below is that it scans the parameters for -d and then stores the text that follows that in the string variable fileDir. It also ignores any other parameters. Any help is appreciated. //Console application Parameters::Parameters(int argc, _TCHAR* argv[]) { _Tstring fileDir; // Is there some kind of _t variable to use here for a string? for (int i = 0; i < argc; i = i + 1) { if (_tccmp(argv[i], _T("-d")) == 0) // this appeared to accept anything starting with - { i = i + 1; fileDir = argv[i] } } _tprintf("Parameter value found: %s\n", fileDir); }

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  • Is there a C# equivalent of typeof for properties/methods/members?

    - by David
    A classes Type metadata can be obtained in several ways. Two of them are: var typeInfo = Type.GetType("MyClass") and var typeInfo = typeof(MyClass) The advantage of the second way is that typos will be caught by the compiler, and the IDE can understand what I'm talking about (allowing features like refactoring to work without silently breaking the code) Does there exist an equivalent way of strongly referencing members/properties/methods for metadata and reflection? Can I replace: var propertyInfo = typeof(MyClass).GetProperty("MyProperty") with something like: var propertyInfo = property(MyClass.MyProperty)

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  • document directory for different iphone app targets

    - by David
    I have two targets for my app which both unarchive serialized objects, however the objects made by the two apps are not compatible. these objects seem to be saved to the same document directory so that one app will try to unarchive the other's objects. how do I get the apps to create separate sandboxes so they do not have access each others' saved objects? or do I need to just have each version create differently named files?

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  • Easily digestible UI tips for developers

    - by David
    What are some key UI design tips that every developer should know? While there are a number of UI resources for developers (for example, Joel Spolsky's User Interface Design for Programmers), I'm interested in more of a bullet list that can be communicated in 1 to 2 pages. I'm interested in more tactical, day-to-day UI tips, as opposed to overarching UI design goals that would be covered in a UI design meeting (presumably attended by at least one person with a good UI sense). A collection of these tips might cover about 80% of the cases that an everyday programmer would come across.

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  • PHP - Why does my computation produce a different result when I assign it to a variable?

    - by David
    I want to round a number to a specific number of significant digits - basically I want the following function: round(12345.67, 2) -> 12000 round(8888, 3) -> 8890 I have the following, but there's a strange problem. function round_to_sf($number, $sf) { $mostsigplace = floor(log10(abs($number)))+1; $num = $number / pow(10, ($mostsigplace-$sf)); echo ($number / pow(10, ($mostsigplace-$sf))).' '.$num.'<BR>'; } round_to_sf(41918.522, 1); Produces the following output: 4.1918522 -0 How can the result of a computation be different when it's assigned to a variable?

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  • Not Equal two Generic Lists

    - by David Johnson
    I have two generic lists, both containing different data, except 4 fields, which I want to compare to another list and find items that do not match in either list. I need to basically replace where it says equals below, with not equals! var unMatchedData = from liveLines in liveList join oldList in comapreSnapshotList on new {liveLines.ClientNo, liveLines.SequenceNo, liveLines.LineNo, liveLines.Text} equals new {oldList.ClientNo, oldList.SequenceNo, oldList.LineNo, oldList.Text} select new KNOWTXTS { ClientNo = liveLines.ClientNo, SequenceNo = liveLines.SequenceNo, LineNo = liveLines.LineNo, Text = liveLines.Text };

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  • LINQ query for tag system: Matching any of several tags?

    - by David Veeneman
    I am just getting started with LINQ. I am creating an Entity Framework app that uses the canonical Post and Tag model. A Post contains an ID, Text, and Tags, and a Tag contains an ID, a Name, and Posts. A previous thread on StackOverflow showed me how to query for a Post that matches all Tag objects (A and B and C) in a search list. But how would I query for a Post that matches any Tag (A or B or C) in the list? Thanks for your help.

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  • Manage more Images to move in View

    - by David Pollak
    hi everyone, I'm creating an app which has more UIImageView on a View, they should move normally from a side to the other. I have an issue: after entering the second image, the two UIImageView start to behave crazy (!) because they don' move freely, but they are like restricted in two different areas not touching each other even if I said different things the first thing that I want to do, is to let them move normally; this is the code I am using: `- (void)viewDidLoad { [super viewDidLoad]; pos = CGPointMake(14.0, 7.0); [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(onTimer) userInfo:nil repeats:YES]; }` - (void) onTimer { pallone.center = CGPointMake(pallone.center.x+pos.x, pallone.center.y+pos.y); if(pallone.center.x > 320 || pallone.center.x < 0) pos.x = -pos.x; if(pallone.center.y > 480 || pallone.center.y < 0) pos.y = -pos.y; } and for the other image that has to enter after: - (IBAction)spara{ cos = CGPointMake(8.0, 4.0); [NSTimer scheduledTimerWithTimeInterval:0.05 target:self selector:@selector(inTimer) userInfo:nil repeats:YES]; } - (void)inTimer{ bomba.center = CGPointMake(bomba.center.x+pos.x, bomba.center.y+pos.y); if(bomba.center.x > 50 || bomba.center.x < 0) pos.x = -pos.x; if(bomba.center.y > 480 || bomba.center.y < 0) pos.y = -pos.y; } what should I change ? and if I'd like the images to move only in one way (y) ? how do I do this ? I know, I'm a newbie thanks in advance

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  • Configure Django project in a subdirectory using mod_python. Admin not working.

    - by David
    HI guys. I was trying to configure my django project in a subdirectory of the root, but didn't get things working.(LOcally it works perfect). I followed the django official django documentarion to deploy a project with mod_python. The real problem is that I am getting "Page not found" errors, whenever I try to go to the admin or any view of my apps. Here is my python.conf file located in /etc/httpd/conf.d/ in Fedora 7 LoadModule python_module modules/mod_python.so SetHandler python-program PythonHandler django.core.handlers.modpython SetEnv DJANGO_SETTINGS_MODULE mysite.settings PythonOption django.root /mysite PythonDebug On PythonPath "['/var/www/vhosts/mysite.com/httpdocs','/var/www/vhosts/mysite.com/httpdocs/mysite'] + sys.path" I know /var/www/ is not the best place to put my django project, but I just want to send a demo of my work in progress to my customer, later I will change the location. For example. If I go to www.domain.com/mysite/ I get the index view I configured in mysite.urls. But I cannot access to my app.urls (www.domain.com/mysite/app/) and any of the admin.urls.(www.domain.com/mysite/admin/) Here is mysite.urls: urlpatterns = patterns('', url(r'^admin/password_reset/$', 'django.contrib.auth.views.password_reset', name='password_reset'), (r'^password_reset/done/$', 'django.contrib.auth.views.password_reset_done'), (r'^reset/(?P<uidb36>[0-9A-Za-z]+)-(?P<token>.+)/$', 'django.contrib.auth.views.password_reset_confirm'), (r'^reset/done/$', 'django.contrib.auth.views.password_reset_complete'), (r'^$', 'app.views.index'), (r'^admin/', include(admin.site.urls)), (r'^app/', include('mysite.app.urls')), (r'^photologue/', include('photologue.urls')), ) I also tried changing admin.site.urls with ''django.contrib.admin.urls' , but it didn't worked. I googled a lot to solve this problem and read how other developers configure their django project, but didn't find too much information to deploy django in a subdirectory. I have the admin enabled in INSTALLED_APPS and the settings.py is ok. Please if you have any guide or telling me what I am doing wrong it will be much appreciated. THanks.

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  • in ruby, how do you make this nested hash work?

    - by David
    this one creates an error: @settings = { :tab1 => { :name => { :required => true }, :description } } need to change :descrpition to :description = {}, but i don't have any values for :description so i want it to remain as is (without the empty = {}) Would you show me the best way to handle this kind of situation? thanks in advance

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  • How to reset keyboard for an entry field?

    - by David.Chu.ca
    I am using tag field as a flag for text fields text view fields for auto-jumping to the next field: - (BOOL)findNextEntryFieldAsResponder:(UIControl *)field { BOOL retVal = NO; for (UIView* aView in mEntryFields) { if (aView.tag == (field.tag + 1)) { [aView becomeFirstResponder]; retVal = YES; break; } } return retVal; } It works fine in terms of auto-jumping to the next field when Next key is pressed. However, my case is that the keyboards are different some fields. For example, one fields is numeric & punctuation, and the next one is default (alphabetic keys). For the numeric & punctuation keyboard is OK, but the next field will stay as the same layout. It requires user to press 123 to go back ABC keyboard. I am not sure if there is any way to reset the keyboard for a field as its keyboard defined in xib? Not sure if there is any APIs available? I guess I have to do something is the following delegate? -(void)textFieldDidBegingEditing:(UITextField*) textField { // reset to the keyboard to request specific keyboard view? .... } OK. I found a solution close to my case by slatvik: -(void) textFieldDidBeginEditing:(UITextField*) textField { textField.keyboardType = UIKeybardTypeAlphabet; } However, in the case of the previous text fields is numeric, the keyboard stays numeric when auto-jumped to the next field. Is there any way to set keyboard to alphabet mode?

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  • Java - StackOverflow Error on recursive 2D boolean array method that shouldn't happen.

    - by David W.
    Hey everyone, I'm working on a runnable java applet that has a fill feature much like the fill method in drawing programs such as Microsoft Paint. This is how my filling method works: 1.) The applet gets the color that the user clicked on using .getRGB 2.) The applet creates a 2D boolean array of all the pixels in the window, with the value "true" if that pixel is the same color as the color clicked on or "false" if not. The point of this step is to keep the .getRGB method out of the recursive method to hopefully prevent this error. 3.) The applet recursively searches the 2D array of booleans where the user clicked, recording each adjacent point that is "true" in an ArrayList. The method then changes each point it records to false and continues. 4.) The applet paints every point stored in the ArrayList to a user selected color. All of the above steps work PERFECTLY if the user clicks within a small area, where only a few thousand pixels or so have their color changed. If the user selects a large area however (such as about 360,000 / the size of the applet window), the applet gets to the recursive stage and then outputs this error: Exception in thread "AWT-EventQueue-1" java.lang.StackOverflowError at java.util.ArrayList.add(ArrayList.java:351) at paint.recursiveSearch(paint.java:185) at paint.recursiveSearch(paint.java:190) at paint.recursiveSearch(paint.java:190) at paint.recursiveSearch(paint.java:190) at paint.recursiveSearch(paint.java:190) at paint.recursiveSearch(paint.java:190) at paint.recursiveSearch(paint.java:190) (continues for a few pages) Here is my recursive code: public void recursiveSearch(boolean [][] list, Point p){ if(isValid(p)){ if(list[(int)p.y][(int)p.x]){ fillPoints.add(p); list[(int)p.y][(int)p.x] = false; recursiveSearch(list, new Point(p.x-1,p.y));//Checks to the left recursiveSearch(list, new Point(p.x,p.y-1));//Checks above recursiveSearch(list, new Point(p.x+1,p.y));//Checks to the right recursiveSearch(list, new Point(p.x,p.y+1));//Checks below } } } Is there any way I can work around an error like this? I know that the loop will never go on forever, it just could take a lot of time. Thanks in advance.

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  • Confused with objects in Ruby

    - by David
    Ruby Newbie here, I understand that everything is an object in Ruby, one thing that I wasn't sure about was understanding Variables. Variables basically give reference to objects (correct me if I'm wrong). During an instructional video, the teacher did a demonstration which went as below: (irb) a = 100 ==> 100 b = a ==> 100 b ==> 100 This part I get, makes total sense. Then he did a = 50 ==> 50 b ==> 100 If B is supposed to point to what a was set which was a 100, why does b still point to 100 if a has now been set as 50?

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  • Sending a large file over network continuously

    - by David Parunakian
    Hello, We need to write software that would continuously (i.e. new data is sent as it becomes available) send very large files (several Tb) to several destinations simultaneously. Some destinations have a dedicated fiber connection to the source, while some do not. Several questions arise: We plan to use TCP sockets for this task. What failover procedure would you recommend in order to handle network outages and dropped connections? What should happen upon upload completion: should the server close the socket? If so, then is it a good design decision to have another daemon provide file checksums on another port? Could you recommend a method to handle corrupted files, aside from downloading them again? Perhaps I could break them into 10Mb chunks and calculate checksums for each chunk separately? Thanks.

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