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• O(N log N) Complexity - Similar to linear?

  - by gav

  Hey All, So I think I'm going to get buried for asking such a trivial but I'm a little confused about something. I have implemented quicksort in Java and C and I was doing some basic comparissons. The graph came out as two straight lines, with the C being 4ms faster than the Java counterpart over 100,000 random integers. The code for my tests can be found here; android-benchmarks I wasn't sure what an (n log n) line would look like but I didn't think it would be straight. I just wanted to check that this is the expected result and that I shouldn't try to find an error in my code. I stuck the formula into excel and for base 10 it seems to be a straight line with a kink at the start. Is this because the difference between log(n) and log(n+1) increases linearly? Thanks, Gav

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• undefined method `events' for #<ActiveRecord::Relation:0x4177518> -rails 3.0.3

  - by brg

  I am having this unexplained NoMethodError with undefined method `events' for #. I don't know why since my model association are well defined and the event table has the foreign keys for the user table. I tried using this fix but it failed: Rails 3 ActiveRecord::Relation random associations behavior event.rb class Event < ActiveRecord::Base belongs_to :user attr_accessible :event_name, :Starts_at, :finish, :tracks end user.rb class User < ActiveRecord::Base has_many :events, :dependent = :destroy attr_accessible :name, :event_attributes accepts_nested_attributes_for :events, :allow_destroy = true end schema.rb ActiveRecord::Schema.define(:version = 20101201180355) do create_table "events", :force = true do |t| t.string "event_name" t.string "tracks" t.datetime "starts_at" t.datetime "finish" t.datetime "created_at" t.datetime "updated_at" t.integer "user_id" end end error message NoMethodError in Users#index undefined method `events' for # Extracted source (around line #10): 7: <%= sortable "Tracks" % 8: 10: <% @users.events.each do |event| % 11: <% debugger % 12: 13: <%= event.starts_at % Trace of template inclusion: app/views/users/index.html.erb Rails.root: C:/rails_project1/events_manager Application Trace | Framework Trace | Full Trace app/views/users/_event_user.html.erb:10:in _app_views_users__event_user_html_erb__412443848_34308540_1390678' app/views/users/index.html.erb:7:in_app_views_users_index_html_erb___603337143_34316016_0'

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• Is it possible to cache all the data in a SQL Server CE database using LinqToSql?

  - by DanM

  I'm using LinqToSql to query a small, simple SQL Server CE database. I've noticed that any operations involving sub-properties are disappointingly slow. For example, if I have a Customer table that is referenced by an Order table, LinqToSql will automatically create an EntitySet<Order> property. This is a nice convenience, allowing me to do things like Customer.Order.Where(o => o.ProductName = "Stopwatch"), but for some reason, SQL Server CE hangs up pretty bad when I try to do stuff like this. One of my queries, which isn't really that complicated takes 3-4 seconds to complete. I can get the speed up to acceptable, even fast, if I just grab the two tables individually and convert them to List<Customer> and List<Order>, then join then manually with my own query, but this is throwing out a lot of what makes LinqToSql so appealing. So, I'm wondering if I can somehow get the whole database into RAM and just query that way, then occasionally save it. Is this possible? How? If not, is there anything else I can do to boost the performance besides resorting to doing all the joins manually? Note: My database in its initial state is about 250K and I don't expect it to grow to more than 1-2Mb. So, loading the data into RAM certainly wouldn't be a problem from a memory point of view. Update Here are the table definitions for the example I used in my question: create table Order ( Id int identity(1, 1) primary key, ProductName ntext null ) create table Customer ( Id int identity(1, 1) primary key, OrderId int null references Order (Id) )

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• What to do with lookup entities selected from drop down select ? How to send them to the service lay

  - by arrages

  I am developing a spring mvc based application. I have a simple pojo form object, the problem is that many properties will be taked from drop down lists that are populated from lookup entities, so I return the entity ID to the form object. public NewCarRequestForm { private makeId; // this are selected from a drop down. private modelId; } Should I just send this lookup entity ID to the service layer? or should I validated that this ID is correct (Somebody can send any random ID through the request) before and how? Now there is a problem if I want to validated something based on some property of the lookup entity. Do I perform a database lookup of the entity just to perform the validation? thanks.

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• Is it possible to use an incremental value within a variable name whilst declaring it within a loop?

  - by Jack

  Hi, I'm creating function which will read different XML files each time that will contain different amounts of the same nodes. I have already created a loop which stores the ID of each node into an array, and now I want to create variables for each array member which store attributes of the node with each ID. Because the number of nodes will be different for every XML document my function reads, I cannot manually assign variables for the attributes of each node ID not knowing how many to assign, so I have created a loop which runs specific to the number of items I have stored in the array. Inside this loop I was hoping to have something like: for (i=0; i<array.length; i++) { var ID + i + width = exampleheight var ID + i + height = exampleheight } I know this doesn't work, but was trying to outline what I am looking to find out. Is it possible to use some kind of variable or random number when declaring a variable?

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• Tree iterator, can you optimize this any further?

  - by Ron

  As a follow up to my original question about a small piece of this code I decided to ask a follow up to see if you can do better then what we came up with so far. The code below iterates over a binary tree (left/right = child/next ). I do believe there is room for one less conditional in here (the down boolean). The fastest answer wins! The cnt statement can be multiple statements so lets make sure this appears only once The child() and next() member functions are about 30x as slow as the hasChild() and hasNext() operations. Keep it iterative <-- dropped this requirement as the recursive solution presented was faster. This is C++ code visit order of the nodes must stay as they are in the example below. ( hit parents first then the children then the 'next' nodes). BaseNodePtr is a boost::shared_ptr as thus assignments are slow, avoid any temporary BaseNodePtr variables. Currently this code takes 5897ms to visit 62200000 nodes in a test tree, calling this function 200,000 times. void processTree (BaseNodePtr current, unsigned int & cnt ) { bool down = true; while ( true ) { if ( down ) { while (true) { cnt++; // this can/will be multiple statesments if (!current->hasChild()) break; current = current->child(); } } if ( current->hasNext() ) { down = true; current = current->next(); } else { down = false; current = current->parent(); if (!current) return; // done. } } }

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• Security issues in accepting passwords vs auto generating the password

  - by Vivekanand Poojari

  Hi, I am developing a console application. This application generates a self signed certificate and installs it in the current machine's certificate store. The steps invlolved are :- Generate a certificate Create a pfx file Install the pfx file For these steps i would need a password for protecting the private key and the pfx file. However these passwords are used only during the execution of the exe. Should I auto generate a password using some random number generation algorithm or accept the password as input from the user? What are the security issues involved in both the scenarios ? Thanks Vivekanand

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• Extreamely fast way to clone the values of an array into a second array?

  - by George

  I am currently working on an application that is responsible for calculating random permutations of a multidemensional array. Currently the bulk of the time in the application is spent copying the array in each iteration (1 million iterations total). On my current system, the entire process takes 50 seconds to complete, 39 of those seconds spent cloning the array. My array cloning routine is the following: public static int[][] CopyArray(this int[][] source) { int[][] destination = new int[source.Length][]; // For each Row for (int y = 0; y < source.Length; y++) { // Initialize Array destination[y] = new int[source[y].Length]; // For each Column for (int x = 0; x < destination[y].Length; x++) { destination[y][x] = source[y][x]; } } return destination; } Is there any way, safe or unsafe, to achieve the same effect as above, much faster?

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• How can I write a function template for all types with a particular type trait?

  - by TC

  Consider the following example: struct Scanner { template <typename T> T get(); }; template <> string Scanner::get() { return string("string"); } template <> int Scanner::get() { return 10; } int main() { Scanner scanner; string s = scanner.get<string>(); int i = scanner.get<int>(); } The Scanner class is used to extract tokens from some source. The above code works fine, but fails when I try to get other integral types like a char or an unsigned int. The code to read these types is exactly the same as the code to read an int. I could just duplicate the code for all other integral types I'd like to read, but I'd rather define one function template for all integral types. I've tried the following: struct Scanner { template <typename T> typename enable_if<boost::is_integral<T>, T>::type get(); }; Which works like a charm, but I am unsure how to get Scanner::get<string>() to function again. So, how can I write code so that I can do scanner.get<string>() and scanner.get<any integral type>() and have a single definition to read all integral types? Update: bonus question: What if I want to accept more than one range of classes based on some traits? For example: how should I approach this problem if I want to have three get functions that accept (i) integral types (ii) floating point types (iii) strings, respectively.

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• C++/Qt - Memory allocation question

  - by HardCoder1986

  Hello! I recently started investigating Qt for myself and have the following question: Suppose I have some QTreeWidget* widget. At some moment I want to add some items to it and this is done via the following call: QList<QTreeWidgetItem*> items; // Prepare the items QTreeWidgetItem* item1 = new QTreeWidgetItem(...); QTreeWidgetItem* item2 = new QTreeWidgetItem(...); items.append(item1); items.append(item2); widget->addTopLevelItems(items); So far it looks ok, but I don't actually understand who should control the objects' lifetime. I should explain this with an example: Let's say, another function calls widget->clear();. I don't know what happens beneath this call but I do think that memory allocated for item1 and item2 doesn't get disposed here, because their ownage wasn't actually transfered. And, bang, we have a memory leak. The question is the following - does Qt have something to offer for this kind of situation? I could use boost::shared_ptr or any other smart pointer and write something like shared_ptr<QTreeWidgetItem> ptr(new QTreeWidgetItem(...)); items.append(ptr.get()); but I don't know if the Qt itself would try to make explicit delete calls on my pointers (which would be disastrous since I state them as shared_ptr-managed). How would you solve this problem? Maybe everything is evident and I miss something really simple?

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• Simple integer encryption

  - by tloflin

  Is there a simple algorithm to encrypt integers? That is, a function E(i,k) that accepts an n-bit integer and a key (of any type) and produces another, unrelated n-bit integer that, when fed into a second function D(i,k) (along with the key) produces the original integer? Obviously there are some simple reversible operations you can perform, but they all seem to produce clearly related outputs (e.g. consecutive inputs lead to consecutive outputs). Also, of course, there are cryptographically strong standard algorithms, but they don't produce small enough outputs (e.g. 32-bit). I know any 32-bit cryptography can be brute-forced, but I'm not looking for something cryptographically strong, just something that looks random. Theoretically speaking it should be possible; after all, I could just create a dictionary by randomly pairing every integer. But I was hoping for something a little less memory-intensive.

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• C Population Count of unsigned 64-bit integer with a maximum value of 15

  - by BitTwiddler1011

  I use a population count (hamming weight) function intensively in a windows c application and have to optimize it as much as possible in order to boost performance. More than half the cases where I use the function I only need to know the value to a maximum of 15. The software will run on a wide range of processors, both old and new. I already make use of the POPCNT instruction when Intel's SSE4.2 or AMD's SSE4a is present, but would like to optimize the software implementation (used as a fall back if no SSE4 is present) as much as possible. Currently I have the following software implementation of the function: inline int population_count64(unsigned __int64 w) { w -= (w 1) & 0x5555555555555555ULL; w = (w & 0x3333333333333333ULL) + ((w 2) & 0x3333333333333333ULL); w = (w + (w 4)) & 0x0f0f0f0f0f0f0f0fULL; return int(w * 0x0101010101010101ULL) 56; } So to summarize: (1) I would like to know if it is possible to optimize this for the case when I only want to know the value to a maximum of 15. (2) Is there a faster software implementation (for both Intel and AMD CPU's) than the function above?

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• What things can I teach a group of children about programming in one day?

  - by Rich Bradshaw

  I'm running a day for 30 kids aged 11-18 about computer game programming. They have all opted to do it, but they have no experience at all of programming. My main aim is for them to learn a few things: programming is hard/challenging programming is something they can learn to do being a computer games programmer != playing games all day a little more insight into how games actually work I'd thought of splitting them into two groups, of younger/less experience and older/more experience, then doing slightly different things. I'd considered showing them Scratch, Game Maker, before showing them the basics of Python and getting them to write a simple text based game (perhaps something like, computer picks a random number, you have to guess it in as few guesses as possible, computer says higher/lower for each guess). Does anyone have any ideas of things to do/show them/ways to teach them?

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• Proper use of use of "cor" function in R

  - by order

  I am interested to know what a proper x (vector matrix or data frame) input looks like. I am currently using the function in two different sorts of matrices. However, I am not sure how R would interpret my data the way I intend. I will explain the types of matrix by example. Type 1 Gene1 Gene2 Gene3 sample1 sample2 Type 2 Sample1 Sample2 Sample3 gene 1 gene 2 gene 3 Are either of these formats valid x parameters? I input both of types of matrices and get some results, but without knowing whether or not this a proper use the function, these are just random numbers. Thank you for your time. I apologize that this isn't more interesting.

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• Portable way of counting milliseconds in C++ ?

  - by ereOn

  Hi, Is there any portable (Windows & Linux) way of counting how many milliseconds elapsed between two calls ? Basically, I want to achieve the same functionnality than the StopWatch class of .NET. (for those who already used it) In a perfect world, I would have used boost::date_time but that's not an option here due to some silly rules I'm enforced to respect. For those who better read code, this is what I'd like to achieve. Timer timer; timer.start(); // Some instructions here timer.stop(); // Print out the elapsed time std::cout << "Elapsed time: " << timer.milliseconds() << "ms" << std::endl; So, if there is a portable (set of) function(s) that can help me implement the Timer class, what is it ? If there is no such function, what Windows & Linux API should I use to achieve this functionnality ? (using #ifdef WINDOWS-like macros) Thanks !

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• ODBC - multiple connections from one app to the same data source

  - by Marcin K

  I vaguely remember reading somewhere (in MSDN ODBC documentation?) that one application cannot make more than one connection to a single data source. It seemed to me that I need one connection that all the threads of the application will have to share. I was trying to look this information up, but I can't seem to find it anymore. Does anyone know/remember how this works? It all might become a problem in our app, since some of its threads will dynamically connect to data sources of their choice. I don't want to see random connection errors if two of them will connect at the same time to one source, so I wanted to double check this info.

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• Address of array vs. address of array[0] - C language

  - by user324994

  My question is why does the address of an array differ from the address of its first position? I'm trying to write my own malloc, but to start out I'm just allocating a chunk of memory and playing around with the addresses. My code looks roughly like this: #define BUFF_SIZE 1024 static char *mallocbuff; int main(){ mallocbuff = malloc(BUFF_SIZE); printf("The address of mallocbuff is %d\n", &mallocbuff); printf("The address of mallocbuff[0] is %d\n", &mallocbuff[0]); } &mallocbuff is the same address every time I run it. &mallocbuff[0] is some random address every time. I was expecting the addresses to match each other. Can anyone explain why this isn't the case?

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• reading partially from sockets

  - by nomad.alien

  I'm having a little test program that sends a lot of udp packets between client-server-client (ping/pong test). The packets are fixed size on each run(last run is max allowable size of udp packet) I'm filling the packets with random data except for the beginning of each packet that contains the packet number. So I'm only interested to see if I receive all the packets back at the client. I'm using sendto() and recvfrom() and I only read the sizeof(packet_number) (which in this case is an int). What happens to the rest of the data? Does it end up in fairyland (gets discarded)? or does the new packet that arrives gets appended to this "old" data? (using linux)

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• Flex Filterfunction - Filter by Array of values

  - by Anandh

  How to filter an Arraycollection by "array of values" rather than a single value (simple comparision) , the below code snippet is for filtering by single value now I went into scenario like filter out only price [10,4,1,8] (some random values from the master collection). Is there any better way to do the second code snippet Filter function simple comparision private function filterForTestData(item:Object):Boolean{ if(item.price < slider.value) return true; else return false; } Filter by array of values private function filterForTestData(item:Object,filterBy:Array= [10,4,1,8]):Boolean{ for(randomprice in filterBy) return item.price == randomprice; } [Edited] Apply Filter testData.filterFunction = filterForTestData;

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• Should I Use GUID or IDENTITY as Thread Number?

  - by user311509

  offerID is the thread # which represents the thread posted. I see in forums posts are represented by random numbers. Is this achieved by IDENTITY? If not, please advice. nvarchar(max) will carry all kind of texts along with HTML tags. CREATE TABLE Offer ( offerID int IDENTITY (4382,15) PRIMARY KEY, memberID int NOT NULL REFERENCES Member(memberID), title nvarchar(200) NOT NULL, thread nvarchar(max) NOT NULL, . . . );

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• start function from another tab in UIWebView

  - by Marjan

  Hello, I have app which have two views implemented in Tabbar, one of them is UIWebView which shows some random html and second is mapView (route-me map), I have function in MapViewController.m which do sth stuff when is clicked on marker label - (void) tapOnLabelForMarker: (RMMarker*) marker onMap: (RMMapView*) map { NSLog(@"taponlabelformarker clicked"); self.tabBarController.selectedIndex=0; WebViewController *web = [[WebViewController alloc] init]; [web dajdasepije]; } and that function should call function which show html in uiwebview tab -(void)dajdasepije { NSLog(@" pokreni me njezno"); [webView loadRequest:[NSURLRequest requestWithURL:[NSURL URLWithString:@"http://www.google.com"]]]; } Problem is that UIWebView never show google page that I asked for it, NSLog prints out at terminal messages that function was called but nothing else happens. Please help, Thanks in advance. Marjan

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• Prevent Apache from answering invalid requests

  - by nickdnk

  I have an Apache web-server that acts as a web front-end for iPhone and iPad applications that communicate by POST and JSON only. Is there any way to prevent Apache from answering requests that are invalid? I can see my error log is filled with attempts to open files such as /admin.php /index.php etc - files that don't exist on my server. I believe this is possible with IIS, but can you do the same thing with Apache? Basically I want the request to appear timed out unless you post exactly the right content to the right file - or at least if you do not request an existing file. This would make the server appear non-existing to everyone but my iPhone users as all communication is SSL and directories are not really guess-able. I did disable the ServerTokens and all that, but I still get File not found etc. when I access the server requesting a random file, which is what these bots do constantly.

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• Can Visual Studio exclude certain folders when searching for header files?

  - by identitycrisisuk

  I'm having trouble with a library that we are using, which has two copies of header files that are needed - one which we are modifying and building from and another which is automatically created during the build process. I don't fully know why or really want to change this but it can cause a bit of annoyance when on random occasions the go to definition function takes you to the auto created header instead of the one used to build. Usually you can spot it but sometimes you don't and make changes to the auto created one, which are then overwritten or sometimes stay around for a while so that something works on your machine but breaks on other peoples. I don't know if there is any way around this as the auto created folder is in the additional include directories of some of the projects in the solution but I just thought I would ask if there was any good way of reducing the chance of this annoying situation cropping up.

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• Jquery Google Maps Problem

  - by Matias

  Here is the problem: Lets say a Jquery toggle button which loads a Google Map upon request and hides its later when toggled: $('#showmeMap').toggle(function() { var map = new GMap2($("#map").get(0)); var mapCenter = new GLatLng(-2, 20); map.setCenter(mapCenter, 12); $('#map').show(); } }, function() { $('#map').hide(); }); Then I add some random markers and later another function which removes markers from the map: $('#destroyMarkersButton').click(function() { for (var i=0; i<gmarkers.length; i++) { map.removeOverlay(gmarkers[i]); } }); When clicking on the button I´ve got the error Map is undefined. My thought was defining Google Map object globally: map = new GMap2($("#map").get(0)); Which works perfectly in Firefox, however, map fails to load on internet explorer!! Any suggestions ?

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• jquery ajax form function(data)

  - by RussP

  Can some one please tell me where I have gone wrong. What ever I do I get the answer "no" JQuery to send data to php query $j.post("logincheck.php",{ username:$j('#username').attr('value'), password:$j('#password').attr('value'), rand:Math.random() } , function(data) { if(data=='yes') {alert('yes');} else {alert('no');} } ); Here is the php query if(isset($_POST['username'])): $username = $_POST['username']; $password = $_POST['password']; $posts = mysql_query("SELECT * FROM users WHERE username='$username'"); $no_rows = mysql_num_rows($posts ); while($row = mysql_fetch_array($posts)): print 'yes'; endwhile; else: print 'no'; //header('location: index.php'); endif; endif; Thank in adance

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