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  • algorithm - How to sort a 0/1 array with 2n/3 comparisons?

    - by Jackson Tale
    In Algorithm Design Manual, there is such an excise 4-26 Consider the problem of sorting a sequence of n 0’s and 1’s using comparisons. For each comparison of two values x and y, the algorithm learns which of x < y, x = y, or x y holds. (a) Give an algorithm to sort in n - 1 comparisons in the worst case. Show that your algorithm is optimal. (b) Give an algorithm to sort in 2n/3 comparisons in the average case (assuming each of the n inputs is 0 or 1 with equal probability). Show that your algorithm is optimal. For (a), I think it is fairly easy. I can choose a[n-1] as pivot, then do something like in quicksort partition, scan 0 to n - 2, find the middle point where left side is all 0 and right side is all 1, this take n - 1 comparisons. But for (b), I can't get a clue. It says "each of the n inputs is 0 or 1 with equal probability", so I guess I can assume the numbers of 0 and 1 equal? But how can I get a result which is related to 1/3? divide the whole array into 3 groups? Thanks

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  • two android threads and not synchronized data

    - by Sponge
    i have a (perhaps stupid) question: im using 2 threads, one is writing floats and one is reading this floats permanently. my question is, what could happen worse when i dont synchronize them? it would be no problem if some of the values would not be correct because they switch just a little every write operation. im running the application this way at the moment and dont have any problems so i want to know what could happen worse? a read/write conflict would cause a number like 12345 which is written to 54321 and red at the same time appear for example as 54345 ? or could happen something worse? (i dont want to use synchronization to keep the code as fast as possible)

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  • client-side data storage and retrieval with html and javascript

    - by pedalpete
    I'm building what I am hoping to be a fairly simple, quick and dirty demo app. So far, I've managed to build a bunch of components using only html and javascript. I know that eventually I'll hook-up a db, but at this point I'm just trying to show off some functionality. In the page, a user can select a bunch of other users (like friends). Then they go to a separate html page and there is some sorting info based on the selected users. So my first attempt was to put the selected users object into a cookie, and retrieve the cookie on the second page. Unfortunately, if the user changed their selection, the cookie wasn't getting updated, and my searches on StackOverflow seemed to say that deleting and updating cookies is unreliable. I tried function updateCookie(updatedUserList){ jQuery.cookie('userList',null); jQuery.cookie('userList',updatedUserList); } but though it set the cookie to null, it wouldn't update it on the second value. So I decided to put the selected users object into a form. Unfortunately, it looks like I can't retrieve the contents from the form on the client-side, only on the server-side. Is there another way to do this? I've worked in PHP and Rails, but I'm trying to do this quickly and simply before building it out into something larger and am trying to avoid any server-side processing for now, which I have managed to do up to this point.

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  • How to duplicate INSERTS into a seperate table?

    - by Ash
    An iPhone application I have installed uses an SQLite database to log entries with basic INSERTS and DELETES being performed on it. However I wish to keep a permanent log of the INSERTS made to this table, so when an INSERT occurs, I want it to be written to another table also as to create a log. I don't have access to the application source code in order to modify the SQL statements made, I do have access to the SQLite database. Can I do this with triggers? If so can somebody provide a short example.

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  • Unit Testing Model Classes that inherits from NSManagedObject

    - by Matt Baker
    So...I'm trying to get unit tests set up in my iPhone App but I'm having some issues. I'm trying to test my model classes but they inherit directly from NSManagedObject. I'm sure this is a problem but I don't know how to get around it. Everything is building and running as expected but I get this error when calling any method on the class I'm testing: Unknown.m:0:0 unrecognized selector sent to instance 0xc2b120 If I follow this structure (http://chanson.livejournal.com/115621.html) to create my object in my tests I end up with another error entirely but it still doesn't help me. Basically my question is this: how can I test a class that inherits from NSManagedObject?

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  • Building a NSPredicate for a filter

    - by John
    Hi, Just wondering what the best way to build a NSPredicate is if some filters are optional? This is basically for a filter, so if some options aren't selected I don't to filter by them eg. If I have option1 and option2 set for the filter. NSPredicate* predicate = [NSPredicate predicateWithFormat:@"option1 = %@ AND option2 = %@] .... otherwise if just option1 NSPredicate* predicate = [NSPredicate predicateWithFormat:@"option1 = %@] .... The key being there are 10 different options to filter, so I don't want to have to code for the 10x10 possible combinations. Thanks

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  • NSManagedObjectContext returns YES for hasChanges when there are none

    - by JK
    I created a separate NSManagedObjectContext on a separate thread to perform some store maintenance. However, I have noticed that the context returns YES for hasChanges as soon as a managed object in it is even referenced e.g. NSString *name = managedObject.name; This context is created and used exclusively in 1 method. Why is it returning has changes, when there there are none?

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  • flex data provider not working if XML has single node value or less

    - by Rees
    hello, i get this error when i retrieve an XML that only has 1 node (no repeating nodes) and i try to store in an ArrayCollection. -When I have MORE than 1 "name" nodes...i do NOT get an error. My test show that XMLListCollection does NOT work either. TypeError: Error #1034: Type Coercion failed: cannot convert "XXXXXX" to mx.collections.ArrayCollection. this error occurs as the line of code: myList= e.result.list.name; Why can't ArrayCollection work with a single node? I'm using this ArrayCollection as a dataprovider for a Component -is there an alternative I can use that will take BOTH single and repeating nodes as well as work as a dataprovider? Thanks in advance! code: [Bindable] private var myList:ArrayCollection= new ArrayCollection(); private function getList(e:Event):void{ var getStudyLoungesService:HTTPService = new HTTPService(); getStuffService.url = "website.com/asdf.php"; getStuffService.addEventListener(ResultEvent.RESULT, onGetList); getStuffService.send(); } private function onGetList(e:ResultEvent):void{ myList= e.result.list.name; }

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  • Customising log4j logging for sensitive data

    - by Xetius
    I have a class which contains sensitive information (Credit card info, phone numbers etc). I want to be able to pass this class to log4j, but have it obscure certain information. If I have a class UserInformation which has getPhoneNumber, getCreditCardNumber methods, how would I customise log4j or this class so that it will obscure the numbers correctly. I want the credit card number to be output as xxxx-xxxx-xxxx-1234 and the phone number to be output as xxxx-xxx-xxx given that these would be 1234-1234-1234-1234 and 1234-567-890 Thanks

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  • Iterative printing over two data types in Python

    - by old Ixfoxleigh
    I often browse freely-available art on the web. Actually, I can't think of a better use for the internet than to turn it into a gigantic art gallery. When I encounter a set of pieces I quite like, I download them all to my hard drive. wget makes that easy, especially in combination with Python's print function, and I use this all the time to make a list of URLs that I then wget. Say I need to download a list of jpegs that run from art0 to art100 in the directory 'art,' I just tell python for i in range(0,101): print "http://somegallery/somedirectory/art", i So, this is probably a fairly simple operation in Python, and after a find-and-replace to remove whitespace, it's just a matter of using wget -i, but in days before I knew any Python I'd slavishly right-click and save. Now I've got a bunch of files from Fredericks & Freiser gallery in New York that all go a(1-14), b(1-14), c(1-14), etc., up to the letter g. I could do that in 7 goes, and it would take me less time than it took to write this SO question. That said, I want to deepen my knowledge of Python. So, given the letters a-g, how do I print a mapping of each letter to the integers 1-14?

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  • Compile a binary file for linking OSX

    - by Satpal
    I'm trying to compile a binary file into a MACH_O object file so that it can be linked it into a dylib. The dylib is written in c/c++. On linux the following command is used: ld -r -b binary -o foo.o foo.bin I have tried various option on OSX but to no avail: ld -r foo.bin -o foo.o gives: ld: warning: -arch not specified ld: warning: ignoring file foo.bin, file was built for unsupported file format which is not the architecture being linked (x86_64) An empty .o file is created ld -arch x86_64 -r foo.bin -o foo.o ld: warning: ignoring file foo.bin, file was built for unsupported file format which is not the architecture being linked (x86_64) Again and empty .o file is created. Checking the files with nm gives: nm foo.o nm: no name list The binary file is actually, firmware that will be downloaded to an external device. Thanks for looking

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  • MySql - set of time stamped data (timestamp,event) calculating events per day

    - by Kevin Ohashi
    I have a table: id, datetime, event i also have table dates: date (Y-m-d format) the problem is some days don't have any events, I would like them to show 0 (or null) SELECT DATE_FORMAT(table.timestamp, '%Y-%m-%d') ydm, count(table.fkUID) FROM `table` where table.fkUID=$var group by ydm; is there some way to join or use conditional statements to make the result show: date|count ---------- 2010-05-23| 5 2010-05-24| 0 <--- this line just doesn't exist in my query. 2010-05-26| 3

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  • CoreData is saving model without the save: method being called

    - by chris
    I have a list of items with a plus button in the navigation bar that opens up a modal window containing a table of the models attributes, that displays a form when the table items are clicked (pretty standard form style). For some reason if I click the plus button to open the form to create a new model, then immediately click the done button, the person model is saved. The action linked to the done button does nothing but call on a delegate method notifying the personListViewController to close the window. The apple docs do state that the model is not saved after calling the insertNewObjectForEntityName: ... Simply creating a managed object does not cause it to be saved to a persistent store. The managed object context acts as a scratchpad. I am at a lost to why this is happening, but every time I click the done button I have a new blank item in the original tableView. I am using SDK v3.1.3 // PersonListViewController - open modal window - (void)addPerson { // Load the new form PersonNewViewController *newController = [[PersonNewViewController alloc] init]; newController.modalFormDelegate = self; [self presentModalViewController:newController animated:YES]; [newController release]; } // PersonFormViewController - (void)viewDidLoad { [super viewDidLoad]; if ( person == nil ) { MyAppDelegate *appDelegate = [[UIApplication sharedApplication] delegate]; self.person = [NSEntityDescription insertNewObjectForEntityForName:@"Person" inManagedObjectContext:appDelegate.managedObjectContext]; } ... UIBarButtonItem *doneButton = [[UIBarButtonItem alloc] initWithBarButtonSystemItem:UIBarButtonSystemItemDone target:self action:@selector(done)]; self.navigationItem.rightBarButtonItem = doneButton; [doneButton release]; } - (IBAction) done { [self.modalFormDelegate didCancel]; } // delegate method in the original listViewController - (void) didCancel { [self dismissModalViewControllerAnimated:YES]; }

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  • Need to Post json data using jQuery.ajax

    - by Anil Bhat
    I have a json of the following format which I need to send in the Ajax request through POST method: { “gbus”: [ { "code": "*" } ], “regions”: [ { "code": "*" } ], “offices”: [ { "code": "*" } ], “contracttypes”: [ { "code": "*" } ], “jobnumbers”: [ { "code": "*" } ], “disciplines”: [ { "code": "*" } ] } Its not working for me, giving 500 error always when I try to submit it. Please suggest if you have any idea.

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  • converting date data type into varchar

    - by Sheetal Inani
    I have some dates fields in table. These columns contain dates in the following format: mmddyy For example: 31/12/2010 00:00:00:0000 I need to import these values into a table which is set to varchar and numeric and formats dates like this: monthName varchar Year numeric(4,0) currently I'm using INSERT INTO [School].[dbo].[TeacherAttendenceDet] ([TeacherCode], [MonthName], [Year]) (SELECT MAX(employeecode), Datename(MONTH, dateofjoining) AS MONTH, Datepart(YEAR, dateofjoining) AS DATE FROM employeedet GROUP BY dateofjoining) but datename() gives result in date format.. I have to save it in varchar format How can I do this? this is employeemast table: EmployeeCode numeric(5, 0) PayScaleCode numeric(7, 0) DesignationCode varchar(50) CityCode numeric(5, 0) EmployeeName varchar(50) FatherName varchar(50) BirthDate varchar(50) DateOfJoining varchar(50) Address varchar(150) this is TeacherAttendenceDet table TeacherCode numeric(5, 0) Unchecked Year numeric(4, 0) Unchecked MonthName varchar(12) Unchecked i have to insert in teacherattendencedet table the monthname and year from employeemast

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  • Big-O for GPS data

    - by HH
    A non-critical GPS module use lists because it needs to be modifiable, new routes added, new distances calculated, continuos comparisons. Well so I thought but my team member wrote something I am very hard to get into. His pseudo code int k =0; a[][] <- create mapModuleNearbyDotList -array //CPU O(n) for(j = 1 to n) // O(nlog(m)) for(i =1 to n) for(k = 1 to n) if(dot is nearby) adj[i][j]=min(adj[i][j], adj[i][k] + adj[k][j]); His ideas transformations of lists to tables His worst case time complexity is O(n^3), where n is number of elements in his so-called table. Exception to the last point with Finite structure: O(mlog(n)) where n is number of vertices and m is an arbitrary constants Questions about his ideas why to waste resources to transform constantly-modified lists to table? Fast? only point where I to some extent agree but cannot understand the same upper limits n for each for-loops -- perhaps he supposed it circular why does the code take O(mlog(n)) to proceed in time as finite structure? The term finite may be wrong, explicit?

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  • NSData in CoreData is not saving properly

    - by abisson
    I am currently trying to store images I download from the web into an NSManagedObject class so that I don't have to redownload it every single time the application is opened. I currently have these two classes. Plant.h @property (nonatomic, retain) NSString * name; @property (nonatomic, retain) PlantPicture *picture; PlantPicture.h @property (nonatomic, retain) NSString * bucketName; @property (nonatomic, retain) NSString * creationDate; @property (nonatomic, retain) NSData * pictureData; @property (nonatomic, retain) NSString * slug; @property (nonatomic, retain) NSString * urlWithBucket; Now I do the following: - (UICollectionViewCell *)collectionView:(UICollectionView *)collectionView cellForItemAtIndexPath:(NSIndexPath *)indexPath { PlantCollectionCell *cell = [collectionView dequeueReusableCellWithReuseIdentifier:CellIdentifier forIndexPath:indexPath]; Plant *plant = [self.fetchedResultsController objectAtIndexPath:indexPath]; cell.plantLabel.text = plant.name; if(plant.picture.pictureData == nil) { NSLog(@"Downloading"); NSMutableString *pictureUrl = [[NSMutableString alloc]initWithString:amazonS3BaseURL]; [pictureUrl appendString:plant.picture.urlWithBucket]; NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:pictureUrl]]; AFImageRequestOperation *imageOperation = [AFImageRequestOperation imageRequestOperationWithRequest:request success:^(UIImage *image) { cell.plantImageView.image = image; plant.picture.pictureData = [[NSData alloc]initWithData:UIImageJPEGRepresentation(image, 1.0)]; NSError *error = nil; if (![_managedObjectContext save:&error]) { NSLog(@"Unresolved error %@, %@", error, [error userInfo]); } }]; [imageOperation start]; } else { NSLog(@"Already"); cell.plantImageView.image = [UIImage imageWithData:plant.picture.pictureData]; } NSLog(@"%@", plant.name); return cell; } The plant information is present, as well as the picture object. However, the NSData itself is NEVER saved throughout the application opening and closing. I always have to REDOWNLOAD the image! Any ideas!? [Very new to CoreData... sorry if it is easy!] thanks!

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  • Basic data alignment question

    - by Broken Logic
    I've been playing around to see how my computer works under the hood. What I'm interested in is seeing is what happens on the stack inside a function. To do this I've written the following toy program: #include <stdio.h> void __cdecl Test1(char a, unsigned long long b, char c) { char c1; unsigned long long b1; char a1; c1 = 'b'; b1 = 4; a1 = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&b1 - (long)&a1, (long)&c1 - (long)&b1, (long)&a - (long)&c1, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&a1 ); }; struct TestStruct { char a; unsigned long long b; char c; }; void __cdecl Test2(char a, unsigned long long b, char c) { TestStruct locals; locals.a = 'b'; locals.b = 4; locals.c = 'r'; printf("%d %d - %d - %d %d Total: %d\n", (long)&locals.b - (long)&locals.a, (long)&locals.c - (long)&locals.b, (long)&a - (long)&locals.c, (long)&b - (long)&a, (long)&c - (long)&b, (long)&c - (long)&locals.a ); }; int main() { Test1('f', 0, 'o'); Test2('f', 0, 'o'); return 0; } And this spits out the following: 9 19 - 13 - 4 8 Total: 53 8 8 - 24 - 4 8 Total: 52 The function args are well behaved but as the calling convention is specified, I'd expect this. But the local variables are a bit wonky. My question is, why wouldn't these be the same? The second call seems to produce a more compact and better aligned stack. Looking at the ASM is unenlightening (at least to me), as the variable addresses are still aliased there. So I guess this is really a question about the assembler itself allocates the stack to local variables. I realise that any specific answer is likely to be platform specific. I'm more interested in a general explanation unless this quirk really is platform specific. For the record though, I'm compiling with VS2010 on a 64bit Intel machine.

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  • Convert.ToSingle() for float data Type

    - by Asim Sajjad
    I have used many of the Convert.To..... functions for conversion , but I didn't understand one thing that for every datatype they have provide a Convert.To function but not for float datatype, in order to convert to float you need to use Convert.ToSingle() , why is this so ?

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  • How do I remove the leaves of a binary tree?

    - by flopex
    I'm trying to remove all of the leaves. I know that leaves have no children, this is what I have so far. public void removeLeaves(BinaryTree n){ if (n.left == null && n.right == null){ n = null; } if (n.left != null) removeLeaves(n.left); if (n.right != null) removeLeaves(n.right); }

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