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• Deletion procedure for a Binary Search Tree

  - by Metz

  Consider the deletion procedure on a BST, when the node to delete has two children. Let's say i always replace it with the node holding the minimum key in its right subtree. The question is: is this procedure commutative? That is, deleting x and then y has the same result than deleting first y and then x? I think the answer is no, but i can't find a counterexample, nor figure out any valid reasoning. EDIT: Maybe i've got to be clearer. Consider the transplant(node x, node y) procedure: it replace x with y (and its subtree). So, if i want to delete a node (say x) which has two children i replace it with the node holding the minimum key in its right subtree: y = minimum(x.right) transplant(y, y.right) // extracts the minimum (it doesn't have left child) y.right = x.right y.left = x.left transplant(x,y) The question was how to prove the procedure above is not commutative.

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• transition of x-axis results in overflow

  - by peter

  First of all, no: this question is not about the (yet) ugly transition of the lines (I might open another one for that, though..). I'm displaying data in line charts and the user can select the time horizon. The x-axis then correspondingly transitions so as to fit to the changed time horizon. In attached image, e.g., the time horizon was 1 week and then I switched to 4 weeks. The number of ticks on the x-axis increases from 7 to 28, correspondingly. Question: How can I prevent the x-axis animation to display outside the svg container? As you can see, the additional dates fly in from the left and they are being animated far far outside the container. Any ideas? Right now, the transition works probably in the most simple way it could: // format for x-axis var xAxis = d3.svg.axis() .scale(x) .orient("bottom") .tickFormat(d3.time.format("%d.%m")) .ticks(d3.time.days, 1) .tickSubdivide(0); // Update x-axis svg.select(".x") .transition() .duration(500) .call(xAxis);

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• How to handle multiple openIDs for the same user

  - by Sinan

  For my site I am using a login system much like the one on SO. A user can login with his Facebook, Google (Gmail openID), Twitter account. This question is not about specific oAuth or openID implementations. The question is how to know if the same user logins with different providers. Let me give an example: Bobo comes to site logins to site by clicking on "Login with Facebook". Because this is his first visit we create an account for him. Later Bobo comes to the site. This time he clicks on "Login with Google". So how do I know if this is the same person so I can add this provider to his account instead of creating a new (and duplicate) account. Can I trust solely on email? What is the best way to handle this. How does SO do it? Any ideas?

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• Why does the rename() syscall prohibit moving a directory that I can't write to a different director

  - by Daniel Papasian

  I am trying to understand why this design decision was made with the rename() syscall in 4.2BSD. There's nothing I'm trying to solve here, just understand the rationale for the behavior itself. 4.2BSD saw the introduction of the rename() syscall for the purpose of allowing atomic renames/moves of files. From 4.3BSD-Reno/src/sys/ufs/ufs_vnops.c: /* * If ".." must be changed (ie the directory gets a new * parent) then the source directory must not be in the * directory heirarchy above the target, as this would * orphan everything below the source directory. Also * the user must have write permission in the source so * as to be able to change "..". We must repeat the call * to namei, as the parent directory is unlocked by the * call to checkpath(). */ if (oldparent != dp->i_number) newparent = dp->i_number; if (doingdirectory && newparent) { VOP_LOCK(fndp->ni_vp); error = ufs_access(fndp->ni_vp, VWRITE, tndp->ni_cred); VOP_UNLOCK(fndp->ni_vp); So clearly this check was added intentionally. My question is - why? Is this behavior supposed to be intuitive? The effect of this is that one cannot move a directory (located in a directory that one can write) that one cannot write to another directory that one can write to atomically. You can, however, create a new directory, move the links over (assuming one has read access to the directory), and then remove one's write bit on the directory. You just can't do so atomically. % cd /tmp % mkdir stackoverflow-question % cd stackoverflow-question % mkdir directory-1 % mkdir directory-2 % mkdir directory-1/directory-i-cant-write % echo "foo" > directory-1/directory-i-cant-write/contents % chmod 000 directory-1/directory-i-cant-write/contents % chmod 000 directory-1/directory-i-cant-write % mv directory-1/directory-i-cant-write directory-2 mv: rename directory-1/directory-i-cant-write to directory-2/directory-i-cant-write: Permission denied We now have a directory I can't write with contents I can't read that I can't move atomically. I can, however, achieve the same effect non-atomically by changing permissions, making the new directory, using ln to create the new links, and changing permissions. (Left as an exercise to the reader) . and .. are special cased already, so I don't particularly buy that it is intuitive that if I can't write a directory I can't "change .." which is what the source suggests. Is there any reason for this besides it being the perceived correct behavior by the author of the code? Is there anything bad that can happen if we let people atomically move directories (that they can't write) between directories that they can write?

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• Reported error code considered SQL Injection?

  - by inquam

  SQL injection that actually runs a SQL command is one thing. But injecting data that doesn't actually run a harmful query but that might tell you something valuable about the database, is that considered SQL injection? Or is it just used as part to construct a valid SQL injection? An example could be set rs = conn.execute("select headline from pressReleases where categoryID = " & cdbl(request("id")) ) Passing this a string that could not be turned into a numeric value would cause Microsoft VBScript runtime error '800a000d' Type mismatch: 'cdbl' which would tell you that the column in question only accepts numeric data and is thus probably of type integer or similar. I seem to find this in a lot of pages discussing SQL injection, but don't really get an answer if this in itself is considered SQL injection. The reason for my question is that I have a scanning tool that report a SQL injection vulnerability and reports a VBScript runtime error '800a000d' as the reason for the finding.

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• Clustering and DB Replication in virtualized (and cloud) environments

  - by devdude

  Both replication and clustering are terms for servers setups with physical (real) servers, usually implemented on a DB or AS level. Now the question: In a virtualized environment with "easy" scalable servers (touching clustering) and a higher availability (DB replication) through the means of high availability of the virtual server by the cloudserver provider, do we really need replication and clustering (as in covering the problems of traditional servers) ? Question is asked from a soultion/application provider viewpoint. Please exclude the need of replication with a business requirement background, eg. the need to replicate a DB at 2 different geographical locations to ensure performance and data. Thanks for your insights !

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• Display continuous dates in Pivot Chart

  - by Douglas

  I have a set of data in a pivot table with date times and events. I've made a pivot chart with this data, and grouped the data by day and year, then display a count of events for each day. So, my horizontal axis goes from 19 March 2007 to 11 May 2010, and my vertical axis is numeric, going from zero to 140. For some days, I have zero events. These days don't seem to be shown on the horizontal axis, so 2008 is narrower than 2009. How do I display a count of zero for days with no events? I'd like my horizontal axis to be continuous, so that it does not miss any days, and every month ends up taking up the same amount of horizontal space. (This question is similar to the unanswered question here, but I'd rather not generate a table of all the days in the last x number of years just to get a smooth plot!)

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• Should I commit or rollback a transaction that creates a temp table, reads, then deletes it?

  - by Triynko

  To select information related to a list of hundreds of IDs... rather than make a huge select statement, I create temp table, insert the ids into it, join it with a table to select the rows matching the IDs, then delete the temp table. So this is essentially a read operation, with no permanent changes made to any persistent database tables. I do this in a transaction, to ensure the temp table is deleted when I'm finished. My question is... what happens when I commit such a transaction vs. let it roll it back? Performance-wise... does the DB engine have to do more work to roll back the transaction vs committing it? Is there even a difference since the only modifications are done to a temp table? Related question here, but doesn't answer my specific case involving temp tables: http://stackoverflow.com/questions/309834/should-i-commit-or-rollback-a-read-transaction

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• Django admin interface upload failing on request data read error

  - by Jake

  Hi All, This is an updated version of an old question I asked. I've now done a lot more testing, plus the old question got hijacked. I'm getting a request data read error when trying to upload files to the Django admin interface. Files under about 150k work, but bigger files always fail and almost always at around 192k (that's 3 chunks) completed, sometimes at around 160k. The Exception I get is below. File "/usr/lib/python2.4/site-packages/django/http/multipartparser.py", line 405, in read return self._file.read(num_bytes) IOError: request data read error I've tried Chrome and Firefox on Windows and Firefox on Mac - Same results. I can upload to other sites so I don't think it's my connection. I'm running python 2.4, django 1.1, mod_wsgi, on CentOS (a media temple DV server) Locally it's fine (Django development server) Everything I've found on this issue says it's a mod_python issue and that changing to mod_wsgi will fix it, but I am running mod_wsgi. Can anyone help?

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• Make a compiled binary run at native speed flawlessly without recompiling from source on a another system?

  - by unknownthreat

  I know that many people, at a first glance of the question, may immediately yell out "Java", but no, I know Java's qualities. Allow me to elaborate my question first. Normally, when we want our program to run at a native speed on a system, whether it be Windows, Mac OS X, or Linux, we need to compile from source codes. If you want to run a program of another system in your system, you need to use a virtual machine or an emulator. While these tools allow you to use the program you need on the non-native OS, they sometimes have problems of performance and glitches. We also have a newer compiler called "JIT Compiler", where the compiler will parse the bytecode program to native machine language before execution. The performance may increase to a very good extent with JIT Compiler, but the performance is still not the same as running it on a native system. Another program on Linux, WINE, is also a good tool for running Windows program on Linux system. I have tried running Team Fortress 2 on it, and tried experiment with some settings. I got ~40 fps on Windows at its mid-high setting on 1280 x 1024. On Linux, I need to turn everything low at 1280 x 1024 to get ~40 fps. There are 2 notable things though: Polygon model settings do not seem to affect framerate whether I set it low or high. When there are post-processing effects or some special effects that require manipulation of drawn pixels of the current frame, the framerate will drop to 10-20 fps. From this point, I can see that normal polygon rendering is just fine, but when it comes to newer rendering methods that requires graphic card to the job, it slows down to a crawl. Anyway, this question is rather theoretical. Is there anything we can do at all? I see that WINE can run STEAM and Team Fortress 2. Although there are flaws, they can run at lower setting. Or perhaps, I should also ask, "is it possible to translate one whole program on a system to another system without recompiling from source and get native speed?" I see that we also have AOT Compiler, is it possible to use it for something like this? Or there are so many constraints (such as DirectX call or differences in software architecture) that make it impossible to have a flawless and not native to the system program that runs at native speed?

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• Help needed with MySQL query to join data spanning multiple tables with data used as column names

  - by gurun8

  I need a little help putting together a SQL query that will give me the following resultsets: and The data model looks like this: The tricky part for me is that the columns to the right of the "Product" in the resultset aren't really columns in the database but rather key/value pairs spanned across the data model. Table data is as follows: My apologies in advance for the image heavy question and the image quality. This just seemed like the easiest way to convey the information. It'll probably take someone less time to write the query statement to achieve the results than it did for me to assemble this question. By the way, the "product_option" table image is truncated but it illustrated the general idea of the data structure. The MySQL server version is 5.1.45.

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• Ajax data two-way data binding strategies?

  - by morgancodes

  I'd like to 1) Draw create form fields and populate them with data from javascript objects 2) Update those backing objects whenever the value of the form field changes Number 1 is easy. I have a few js template systems I've been using that work quite nicely. Number 2 may require a bit of thought. A quick google search on "ajax data binding" turned up a few systems which seem basically one-way. They're designed to update a UI based on backing js objects, but don't seem to address the question of how to update those backing objects when changes are made to the UI. Can anyone recommend any libraries which will do this for me? It's something I can write myself without too much trouble, but if this question has already been thought through, I'd rather not duplicate the work.

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• Whats the scope of a c function defined within objective-c class?

  - by roja

  I was reading up about bypassing objective-c's messaging to gain performance (irrelevant to this specific question) when i found an interesting bit of code: #import <Cocoa/Cocoa.h> @interface Fib : NSObject { } - (long long) cFib: (NSUInteger) number; @end @implementation Fib // c implementation of fib long long cFibIMP(NSUInteger number) { return (number < 3) ? 1 : cFib(number - 1) + cFib(number - 2); } // method wrapper for c implementation of fib - (long long) cFib: (NSUInteger) number { return cFibIMP(number); } @end My question is; when using c function, within an objective-c object, what scope is the c function (cFibIMP in this particular case) placed in? Does the objective-c class encapsulate the c function removing change of name-clash or is the c function simply dumped into the global scope of the whole objective-c program?

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• RedDot with Lotus Notes support

  - by fredde

  Hi, First post here in SO. I have a question within the area of CMS (RedDot) and possible integration of some Lotus Notes functionality. I'm very fresh in both areas. From my short research (did not find very much material regarding RedDot) I got the following: Contents in RedDot CMS can be accessed (and modified?) via the RQL API. (basicly xml messages) There exists a API developed for Java (jRQL). Lotus Notes has a developer kit called Lotus Expeditor Toolkit. My vague question is something like this: Is it possible to integrate a some kind of "content approver/manager" or any other useful CMS functionality from Lotus Notes into the RedDot CMS system? In that case I was thinking of using the jRQL and Lotus Expediton Toolkit so that the back end is fully using Java. Or is there any better solution? Regards Fredrik

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• LINQ-to-SQL vs stored procedures?

  - by scottmarlowe

  I took a look at the "Beginner's Guide to LINQ" post here on StackOverflow (http://stackoverflow.com/questions/8050/beginners-guide-to-linq), but had a follow-up question: We're about to ramp up a new project where nearly all of our database op's will be fairly simple data retrievals (there's another segment of the project which already writes the data). Most of our other projects up to this point make use of stored procedures for such things. However, I'd like to leverage LINQ-to-SQL if it makes more sense. So, the question is this: For simple data retrievals, which approach is better, LINQ-to-SQL or stored procs? Any specific pro's or con's? Thanks.

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• How can I modify a custom object in an ASP.NET FormView based on a button click?

  - by David

  I have a FormView that modifies an instance of a custom class. The various form controls (TextBox, DropDownList etc.) are working fine. However, I want to include a Button that will modify the state of the DataItem based on some very simple logic. There is no form control which could control this change in a non-confusing way. So I tried adding a Button and modifying the state of the DataItem in the code-behind. But the problem I encounter is that the FormView's DataItem is null/nothing. From reading this SO question it seems the problem is that the item is not databound when the Button's Click event is fired. So, the question; Is it possible to get the DataItem for the FormView during a Button's Click event? and if not: what are my options for implementing this? Thanks in advance. Edit: I can include any code that might help

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• Significant new inventions in computing since 1980

  - by Alan Kay

  This question arose from comments about different kinds of progress in computing over the last 50 years or so. I was asked by some of the other participants to raise it as a question to the whole forum. Basic idea here is not to bash the current state of things but to try to understand something about the progress of coming up with fundamental new ideas and principles. I claim that we need really new ideas in most areas of computing, and I would like to know of any important and powerful ones that have been done recently. If we can't really find them, then we should ask "Why?" and "What should we be doing?"

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• RadCombox Client Side Input ID Server Side

  - by francisf

  Hi All, Question 1 : RadComboBox i need to find the ID of the Input element at the Server side . The telerik provides a way to find the ID of the input element() client side. But i nned to find the ID at the server side . Question 2 : I have a radcombobox to a radgrid and am attaching a client event on itemdatabound for ex discCombo.OnClientLoad = "LoaderDisc" I need to find a way to an argument to this method say an id of another control ?.How do i pass my arguments to the combobox client event ? Thanks, Francis P.

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• Is this type of calculation to be put in Model or Controller?

  - by Hadi

  i have Product and SalesOrder model (to simplify, 1 sales_order only for 1 product) Product has_many SalesOrder SalesOrder belongs_to Product pa = Product A #2000 so1 = SalesOrder 1 order product A #1000, date:yesterday so2 = SalesOrder 2 order product A #999, date:yesterday so3 = SalesOrder 3 order product A #1000, date:now Based on the date, pa.find_sales_orders_that_can_be_delivered will give: SalesOrder 1 order product A #1000, date:yesterday SalesOrder 2 order product A #999, date:yesterday SalesOrder 3 order product A #1, date:now <-- the newest The question is: is find_sales_orders_that_can_be_delivered should be in the Model? i can do it in controller. and the general question is: what goes in Model and what goes in Controller. Thank you

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• Set value in controller using nested resource

  - by vectran

  I have two models, product and order. Product - cost - id Order - cost - product_id Each time someone places an order, it captures the product_id through a radio button value in the "new order" form. In the controller when creating the new order it needs to set order.cost to order.product.cost. Logically I thought the code should be something like this: def create ... @order.cost == @order.product.cost ... end However I can't seem to make it work at all, hence me asking the question here. Any help is answering (or naming) the question would be greatly appreciated.

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• SQL syntax Newbie student

  - by sammysmall

  Describe the output of the following SQL query: select custId, name from customer where region = "New York" UNION select cust.custId, cust.name from customer cust where cust.custId IN (select cust_order.custId from customer_order cust_order, company_employee comp_emp where cust_order.salesEmpId = comp_emp.empId AND comp_emp.name = 'DANIEL'); My question is: at line from customer cust is cust referring to a column in the customer table... This is a homework question I have identified the components leading up to this line and I think that cust is a column in the customer table... I am not asking for an overall solution just a bit of encouragement if I am on the right track...

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• How do I properly implement Unicode passwords?

  - by Sorin Sbarnea

  Adding support for Unicode passwords it an important feature that should not be ignored by the developpers. Still adding support for Unicode in the passwords it's a tricky job because the same text can be encoded in different ways in Unicode and this is not something you may want to prevent people from logging in due to this. Let's say that you'll store the passwords os UTF-8. Now the question is how you should normalize the Unicode data? You had to be sure that you'll be able to compare it. You need to be sure that when the next Unicode standard will be released it will not invalidate your password verification. Note: still there are some places where Unicode passwords are probably never be used, but this question is not about why or when to use Unicode passwords, is about how to implement them the proper way.

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• How would one use Cocos2d to create a game like this.

  - by John Stewart

  http://itunes.apple.com/us/app/angry-birds/id343200656?mt=8&ign-mpt=uo%3D6 So I am getting started with this all game dev thing on iphone and I decided that I will start playing with Cocos2d as my starting engine. Now just so i have a goal in mind, I picked angry birds as my initial target of what sort of game play would I like to learn to build. This is not going to be a market release game. This is totally going to be learning purposes only. So to start off my question is: Would something like this be achievable using Cocos2d? How would I go about building the physics for this? How can one do a screen scroll like the way they do in cocos2d? (any example code would be great) This is just to start off. If you have any particular questions please do add to this question.

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• Test if single linked list is circular by traversing it only once

  - by user1589754

  I am a fresher and I was asked this question in a recent interview I gave. The question was --- By traversing each element of linked list just once find if the single linked list is circular at any point. To this I answered that we will store reference of each node while traversing the list in another linked list and for every node in the list being tested we will find if the reference exists in the list I am storing the references. The interviewer said that he needs a more optimized way to solve this problem. Can anyone please tell me what would be a more optimized method to solve this problem.

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• Java: using endpoint to publish webservice to tomcat server

  - by Will

  hi all, i am creating a simple SOAP web service. i am to ensure that it runs on a tomcat web service. im trying to implement this with JAX-WS (see code) my question is: does the Endpoint.publish use the tomcat server to host this or is it a mini glassfish kind of server? should i be extending UnicastRemoveObject or something similiar instead? ideally it would be able to be packaged into a .WAR and dropped in the directory and just work. It doesn't seem to work with my installed tomcat server as is because it says the port is already in use. I'm using Ubuntu karmic with the tomcat6 package installed, it could also be my user doesnt have permissions to publish to the running tomcat on 8080 i hope this question is clear enough sample code: @WebService public class UserAttributes { public static void main(String[] args) { UserAttributes instance = new UserAttributes(); Endpoint.publish("http://localhost:8082/WebServices/userattributes", instance); } public string Hello() { return "Hello World"; } }

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