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Articles indexed in December 2010

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Do ruby on rails programmers refactor?

- by JoaoHornburg

I'm a Java programmer who started programming Ruby on Rails one year ago. I like the language, rails itself and the principles behind them. But something that bothers me is that Ruby programmers don't seem to refactor. I noticed that there is a big lack of tools for refactoring in Ruby / Rails. Some IDE's, like Aptana and RubyMine seem to offer some very basic refactoring, but nothing really big compared to Eclipse's Java refactorings. Then there is another fact: most railers (even the pros) prefer some lightweight editors, like VIM or TextMate, instead of IDEs. Well, with these tools you just get zero refactoring (only regex with find/replace). This leaves me this impression that rails programmers don't refactor. It might be just a false impression, of course, but I would like to hear the opinion of people who work professionally with ruby on rails. Do you refactor? If you do, how do you do it,with which tools? If not, why not?

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[Ext.tree.TreePanel] getNodeById does not work

- by Moon

Hi, I have a ext treepanel with json. var tree = new Ext.tree.TreePanel({ renderTo:'tree-container', title: 'Category', height: 300, width: 400, useArrows:true, autoScroll:true, animate:true, enableDD:true, containerScroll: true, rootVisible: false, frame: true, root: { text: 'Category', draggable: false, id: '0' }, // auto create TreeLoader dataUrl: $("#web").val() + "/category/index/get-nodes", listeners: { 'checkchange': function(node, checked){ if(checked){ categoryManager.add(node.id); //node.getUI().addClass('complete'); }else{ categoryManager.remove(node.id); // node.getUI().removeClass('complete'); } } } }); dataUrl loads the following json code [{"text":"Code Snippet","id":"1","cls":"folder","checked":false,"children":[{"text":"PHP","id":"3","cls":"file","checked":false,"children":[]},{"text":"Javascript","id":"4","cls":"file","checked":false,"children":[]}]}] when I try to find a node by console.log( tree.getNodeByid(3) ), it shows that it is undefined. Do I have a problem with my code?

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Is man-in-the-middle attack a security threat during SSH authentication using keys?

- by JP19

Hi, I am no expert in network security, so pardon if this question is not very smart :). I am automating logins to some machines using ssh. I am currently avoiding host-key warnings using StrictHostKeyChecking no. I naively understand that someone can impersonate as the server and I risk losing my password to him if that were the case. However, if I am using only public/private Key based authentication ( using PasswordAuthentication no ), can the intruder still cause harm? So basically, with ssh -o "StrictHostKeyChecking no" -o "PasswordAuthentication no" : 1) Can the intruder decipher my private key? 2) Are there any other security threats? regards, JP

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CSS, fill all div width with text

- by lolalola

Hi, How to automatically change the space between the letters.I want the text to take up the entire width of the div. Text is not static. (Always changing text, can be 123" or "text text"...) <style type="text/css"> #menu{ width: 200px; background-color: #000; color: #336699; font-size: 16px; letter-spacing: 100%; } </style> <body> <div id="menu"> tekstas </div>

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PHP OOP singleton doesn't return object

- by Misiur

Weird trouble. I've used singleton multiple times but this particular case just doesn't want to work. Dump says that instance is null. define('ROOT', "/"); define('INC', 'includes/'); define('CLS', 'classes/'); require_once(CLS.'Core/Core.class.php'); $core = Core::getInstance(); var_dump($core->instance); $core->settings(INC.'config.php'); $core->go(); Core class class Core { static $instance; public $db; public $created = false; private function __construct() { $this->created = true; } static function getInstance() { if(!self::$instance) { self::$instance = new Core(); } else { return self::$instance; } } public function settings($path = null) { ... } public function go() { ... } } Error code Fatal error: Call to a member function settings() on a non-object in path It's possibly some stupid typo, but I don't have any errors in my editor. Thanks for the fast responses as always.

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error: no matching function for call to ‘BSTreeNode<int, int>::BSTreeNode(int, int, NULL, NULL)’ - what's wrong?

- by Alexander Suraphel

error: no matching function for call to ‘BSTreeNode::BSTreeNode(int, int, NULL, NULL)’ candidates are: BSTreeNode::BSTreeNode(KF, DT&, BSTreeNode*, BSTreeNode*) [with KF = int, DT = int] here is how I used it: BSTreeNode<int, int> newNode(5,9, NULL, NULL) ; I defined it as follows: BSTreeNode(KF sKey, DT &data, BSTreeNode *lt, BSTreeNode *rt):key(sKey),dataItem(data), left(lt), right(rt){} what's wrong with using my constructor this way? i've been pulling out my hair all night please help me ASAP!!

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Javascript inherance and use of super: is this possible?

- by Totty

var Parent = function(value){ this.value = value; this.value1 = 3; this.hello = function(text){ alert(this.value1 + text); } } var Child = extends(Parent, function(value){ this.value1 = 1; this.hello = function(text){ this.super.hello(text); alert('Child' + this.value1 + this.value); } }) var child = new Child(2); child.hello('ola'); // this must output 2 alerts: // 1: "1ola" // 2: "Child1ola"

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Problem setting row backgrounds in Android Listview

- by zchtodd

I have an application in which I'd like one row at a time to have a certain color. This seems to work about 95% of the time, but sometimes instead of having just one row with this color, it will allow multiple rows to have the color. Specifically, a row is set to have the "special" color when it is tapped. In rare instances, the last row tapped will retain the color despite a call to setBackgroundColor attempting to make it otherwise. private OnItemClickListener mDirectoryListener = new OnItemClickListener(){ public void onItemClick(AdapterView parent, View view, int pos, long id){ if (stdir.getStationCount() == pos) { stdir.moreStations(); return; } if (playingView != null) playingView.setBackgroundColor(Color.DKGRAY); view.setBackgroundColor(Color.MAGENTA); playingView = view; playStation(pos); } }; I have confirmed with print statements that the code setting the row to gray is always called. Can anyone imagine a reason why this code might intermittently fail? If there is a pattern or condition that causes it, I can't tell. I thought it might have something to do with the activity lifecycle setting the "playingView" variable back to null, but I can't reliably reproduce the problem by switching activities or locking the phone. private class DirectoryAdapter extends ArrayAdapter { private ArrayList<Station> items; public DirectoryAdapter(Context c, int resLayoutId, ArrayList<Station> stations){ super(c, resLayoutId, stations); this.items = stations; } public int getCount(){ return items.size() + 1; } public View getView(int position, View convertView, ViewGroup parent){ View v = convertView; LayoutInflater vi = (LayoutInflater)getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); if (position == this.items.size()) { v = vi.inflate(R.layout.morerow, null); return v; } Station station = this.items.get(position); v = vi.inflate(R.layout.songrow, null); if (station.playing) v.setBackgroundColor(Color.MAGENTA); else if (station.visited) v.setBackgroundColor(Color.DKGRAY); else v.setBackgroundColor(Color.BLACK); TextView title = (TextView)v.findViewById(R.id.title); title.setText(station.name); return v; } };

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Symfony: Routing 'secure' and 'login' actions to another application

- by Darmen

Hello, Suppose we have 3 apps - appMain, app1 and app2. Applications 1 and 2 are protected, they have is_secure: true and everything works fine with sfDoctrineGuard plugin. A behavior I want to achieve is when a user is not authenticated, current application to forward him to another one, say appMain with defined module and action. Is that possible? Or can someone tell me where to dig about security mechanisms in symfony?

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How to call another class's method from my app delegate

- by Jared

I have an application that utilizes UILocalNotifications to pop-up UIAlertViews. When the notification fires, the user chooses to go into the app, and this method is called from my app delegate: - (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {...} Where I can handle it and where I also prompt another alertview for more information. So when the app launches, it is displaying view A, and then the alertview pops up and prompts for input. This alertview, however, is originating from my app delegate. I need to be able to reload view A when the user hits Yes/No on the alertview. How can I do that from within my app delegate? Any help is appreciated!!

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Blit Queue Optimization Algorithm

- by martona

I'm looking to implement a module that manages a blit queue. There's a single surface, and portions of this surface (bounded by rectangles) are copied to elsewhere within the surface: add_blt(rect src, point dst); There can be any number of operations posted, in order, to the queue. Eventually the user of the queue will stop posting blits, and ask for an optimal set of operations to actually perform on the surface. The task of the module is to ensure that no pixel is copied unnecessarily. This gets tricky because of overlaps of course. A blit could re-blit a previously copied pixel. Ideally blit operations would be subdivided in the optimization phase in such a way that every block goes to its final place with a single operation. It's tricky but not impossible to put this together. I'm just trying to not reinvent the wheel. I looked around on the 'net, and the only thing I found was the SDL_BlitPool Library which assumes that the source surface differs from the destination. It also does a lot of grunt work, seemingly unnecessarily: regions and similar building blocks are a given. I'm looking for something higher-level. Of course, I'm not going to look a gift horse in the mouth, and I also don't mind doing actual work... If someone can come forward with a basic idea that makes this problem seem less complex than it does right now, that'd be awesome too. EDIT: Thinking about aaronasterling's answer... could this work? Implement customized region handler code that can maintain metadata for every rectangle it contains. When the region handler splits up a rectangle, it will automatically associate the metadata of this rectangle with the resulting sub-rectangles. When the optimization run starts, create an empty region handled by the above customized code, call this the master region Iterate through the blt queue, and for every entry: Let srcrect be the source rectangle for the blt beng examined Get the intersection of srcrect and master region into temp region Remove temp region from master region, so master region no longer covers temp region Promote srcrect to a region (srcrgn) and subtract temp region from it Offset temp region and srcrgn with the vector of the current blt: their union will cover the destination area of the current blt Add to master region all rects in temp region, retaining the original source metadata (step one of adding the current blt to the master region) Add to master region all rects in srcrgn, adding the source information for the current blt (step two of adding the current blt to the master region) Optimize master region by checking if adjacent sub-rectangles that are merge candidates have the same metadata. Two sub-rectangles are merge candidates if (r1.x1 == r2.x1 && r1.x2 == r2.x2) | (r1.y1 == r2.y1 && r1.y2 == r2.y2). If yes, combine them. Enumerate master region's sub-rectangles. Every rectangle returned is an optimized blt operation destination. The associated metadata is the blt operation`s source.

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What is the smallest amount of bits you can write twin-prime calculation?

- by HH

A succinct example in Python, its source. Explanation about the syntactic sugar here. s=p=1;exec"if s%p*s%~-~p:print`p`+','+`p+2`\ns*=p*p;p+=2\n"*999 The smallest amount of bits is defined by the smallest amount of 4pcs of things you can see with hexdump, it is not that precise measure but well-enough until an ambiguity. $ echo 's=p=1;exec"if s%p*s%~-~p:print`p`+','+`p+2`\ns*=p*p;p+=2\n"*999' > .test $ hexdump .test | wc 5 36 200 $ hexdump .test 0000000 3d73 3d70 3b31 7865 6365 6922 2066 2573 0000010 2a70 2573 2d7e 707e 703a 6972 746e 7060 0000020 2b60 2b2c 7060 322b 5c60 736e 3d2a 2a70 0000030 3b70 2b70 323d 6e5c 2a22 3939 0a39 000003e so in this case it is 31 because the initial parts are removed.

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SQLiteOpenHelper problem

- by Harsha M V

I have created SQLiteOpenHelper class to help me open write the database. but i am not able to invoke it from the main.java activity I have created an Class which extends the Database Helper which is stored at /Messaging/src/com/v3/messaging/DatabaseHelper.java Code: http://pastebin.com/Z5qp32xu now i have this class called Main.java which will be the first activity on the launch of the application. But how can i make the DatabaseHelper.java run just to create the database but still be at the Main.java file. The database should be created with the tables only when the db or the tables dont exist. Main.java code: http://pastebin.com/LVFVuhA0 Now when i run the program. the database is not being created :( I am trying to learn Android. So please excuse me if i forgot to tell something.

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New apache on mac

- by Keith

I have installed php5 apache2 mysql5 and postgresql84 using MacPorts. I realize my mac already has apache but it didn't have apache2 nor postgesql hooked up to use with php. I want to not use the default apple apache and use the new macports install. How do I tell my computer to stop looking at the old apache? When I do apachectl in the terminal I believe it is using the old apache. I would like to hook it up to use the new one. How would I do that? The new stuff is installed at /opt/local/apache2 and the old stuff is installed at /private/etc/apache2 I went to system preferences...Sharing...and shut off Web Sharing but when I do apachectl's that turns it on and off in the preferences. I'm running in Snow Leopard.

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HVM virtualization with PV drivers on XenServer

- by Nathan

Is it possible to create an HVM guest in XenServer 5.5 that uses PV drivers for disk and network without being fully paravirutalized? This should give me decent performance from the VM without having to jump through hoops to create a PV guest when a pre-built template doesn't exist. Since PV drivers exist for Windows, and XenServer provides templates for windows that use HVM virtualization this must be possible, I just don't see how to configure this myself.

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Using sed to convert hex characters in postgresql dump file

- by Bernt

I am working on moving several databases from a Postgresql 8.3 server to a Postgresql 8.4 server. It has worked fine so far, but one base has given me some trouble. The database is listed as unicode-encoded in the 8.3-server, but somehow a client program has managed to inject some invalid unicode data into it. When I do a normal dump and restore using postgres' custom format, the new server won't accept it, complaining about unicode errors. My plan is to do a plain text dump of the database, then use sed to replace the invalid characters with nothing (they are not needed). But how do you make sed work on hex/binary values in a file?

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Postgres pgpass windows - not working

- by Scott

DB: Postgres 9.0 Client: Windows 7 Server Windows 2008, 64bit I'm trying to connect remotely to a postgres instance for purposes of performing a pg_dump to my local machine. Everything works from my client machine, except that I need to provide a password at the password prompt, and I'd ultimately like to batch this with a script. I've followed the instructions here: http://www.postgresql.org/docs/current/static/libpq-pgpass.html but it's not working. To recap, I've created a file on the client (and tried the server as well): C:/Users/postgres/AppData/postgresql/pgpass.conf, where postgresql is the db user. The file has one line with the following data: *:5432:*postgres:[mypassword] (also tried explicit ip/dbname values, all asterisks, and every combination in between. (I've also tried replacing each '*' with [localhost|myip] and [mydatabasename] respectively. From my client machine, I connect using: pg_dump -h [myip] -U postgres -w [mydbname] [mylocaldumpfile] I'm presuming that I need to provide the '-w' switch in order to ignore password prompt, at which point it should look in the AppData directory on the server. It just comes back with "connection to database failed: fe_sendauth: no password supplied. Any insights are appreciated. As a hack workaround, if there was a way I could tell the windows batch file on my client machine to inject the password at the postgres prompt, that would work as well. Thanks.

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How to increase the disk cache of Windows 7

- by Mark Christiaens

Under Windows 7 (64 bit), I'm reading through 9000 moderately sized files. In total, there is more than 200 MB of data. Using Java (JDK 1.6.21) I'm iterating over the files. The first 1400 or so go at full speed but then speed drops off to 4ms per file. It turns out that the main cost is incurred simply by opening the files. I'm opening the files using new FileInputStream (and of course closing them in time to avoid file leaks). After some investigating, I see that Windows' disk cache is using only 100 MB or so of RAM although I have 8 GiB available. I've tried increasing the cache size using the CacheSet tool but any values I provide are considered out of range. I've also tried enabling the LargeSystemCache registry key but (after rebooting) the CacheSet tool still indicates I'm using 100 MB of cache (and doesn't increase during the test run). Does anybody have any suggestions to "encourage" Windows 7 to cache my 9000 files?

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Handling Configuration Changes in Windows Azure Applications

- by Your DisplayName here!

While finalizing StarterSTS 1.5, I had a closer look at lifetime and configuration management in Windows Azure. (this is no new information – just some bits and pieces compiled at one single place – plus a bit of reality check) When dealing with lifetime management (and especially configuration changes), there are two mechanisms in Windows Azure – a RoleEntryPoint derived class and a couple of events on the RoleEnvironment class. You can find good documentation about RoleEntryPoint here. The RoleEnvironment class features two events that deal with configuration changes – Changing and Changed. Whenever a configuration change gets pushed out by the fabric controller (either changes in the settings section or the instance count of a role) the Changing event gets fired. The event handler receives an instance of the RoleEnvironmentChangingEventArgs type. This contains a collection of type RoleEnvironmentChange. This in turn is a base class for two other classes that detail the two types of possible configuration changes I mentioned above: RoleEnvironmentConfigurationSettingsChange (configuration settings) and RoleEnvironmentTopologyChange (instance count). The two respective classes contain information about which configuration setting and which role has been changed. Furthermore the Changing event can trigger a role recycle (aka reboot) by setting EventArgs.Cancel to true. So your typical job in the Changing event handler is to figure if your application can handle these configuration changes at runtime, or if you rather want a clean restart. Prior to the SDK 1.3 VS Templates – the following code was generated to reboot if any configuration settings have changed: private void RoleEnvironmentChanging(object sender, RoleEnvironmentChangingEventArgs e) { // If a configuration setting is changing if (e.Changes.Any(change => change is RoleEnvironmentConfigurationSettingChange)) { // Set e.Cancel to true to restart this role instance e.Cancel = true; } } This is a little drastic as a default since most applications will work just fine with changed configuration – maybe that’s the reason this code has gone away in the 1.3 SDK templates (more). The Changed event gets fired after the configuration changes have been applied. Again the changes will get passed in just like in the Changing event. But from this point on RoleEnvironment.GetConfigurationSettingValue() will return the new values. You can still decide to recycle if some change was so drastic that you need a restart. You can use RoleEnvironment.RequestRecycle() for that (more). As a rule of thumb: When you always use GetConfigurationSettingValue to read from configuration (and there is no bigger state involved) – you typically don’t need to recycle. In the case of StarterSTS, I had to abstract away the physical configuration system and read the actual configuration (either from web.config or the Azure service configuration) at startup. I then cache the configuration settings in memory. This means I indeed need to take action when configuration changes – so in my case I simply clear the cache, and the new config values get read on the next access to my internal configuration object. No downtime – nice! Gotcha A very natural place to hook up the RoleEnvironment lifetime events is the RoleEntryPoint derived class. But with the move to the full IIS model in 1.3 – the RoleEntryPoint methods get executed in a different AppDomain (even in a different process) – see here.. You might no be able to call into your application code to e.g. clear a cache. Keep that in mind! In this case you need to handle these events from e.g. global.asax.

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Android App: Proximity

- by Eclipser

Is there an API for Android that will find other people nearby running the same app? For instance, if you were to perform a "scan" it tries to find other people running the same app nearby. Would it be possible to perform the same task across multiple OS (Android, iPhone, Windows, etc.)? Or would the best way be to just have the app communicate to a server your location and have a server-side app that pushes a list of others nearby??? My goal is to find an easy way to eventually transmit data between two devices contigent on those that are nearby.

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Django json serialization problem

- by codingJoe

I am having difficulty serializing a django object. The problem is that there are foreign keys. I want the serialization to have data from the referenced object, not just the index. For example, I would like the sponsor data field to say "sponsor.last_name, sponsor.first_name" rather than "13". How can I fix my serialization? json data: {"totalCount":"2","activities":[{"pk": 1, "model": "app.activity", "fields": {"activity_date": "2010-12-20", "description": "my activity", "sponsor": 13, "location": 1, .... model code: class Activity(models.Model): activity_date = models.DateField() description = models.CharField(max_length=200) sponsor = models.ForeignKey(Sponsor) location = models.ForeignKey(Location) class Sponsor(models.Model): last_name = models.CharField(max_length=20) first_name= models.CharField(max_length=20) specialty = models.CharField(max_length=100) class Location(models.Model): location_num = models.IntegerField(primary_key=True) location_name = models.CharField(max_length=100) def activityJSON(request): activities = Activity.objects.all() total = activities.count() activities_json = serializers.serialize("json", activities) data = "{\"totalCount\":\"%s\",\"activities\":%s}" % (total, activities_json) return HttpResponse(data, mimetype="application/json")

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recommend a server side technology for gwt (beginner)

- by user486503

hi all ! I am developing a gwt project and am looking for an appropriate server side technology. it should support be open source and support user login (and not using openID...) with password recovery etc it seems that the de-facto standard would be spring + hibernate. however, I am unfamiliar with neither of them and understand that the learning curve (especially for spring) is very high. gwt was quite easy to learn using GOOG's excellent online tutorials but the spring equivalent seem to impose lots of configuration files and deeper understanding of its internals. so I am looking for a simpler server side technology to deploy my gwt app. I am definitely prepared to learn a new framework if necessary but not something that would take me 2 months just to understand the fundamentals... any ideas...?

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How do tools like Hiphop for PHP deal with heterogenous arrays?

- by Derek Thurn

I think HipHop for PHP is an interesting tool. It essentially converts PHP code into C++ code. Cross compiling in this manner seems like a great idea, but I have to wonder, how do they overcome the fundamental differences between the two type systems? One specific example of my general question is heterogeneous data structures. Statically typed languages don't tend to let you put arbitrary types into an array or other container because they need to be able to figure out the types on the other end. If I have a PHP array like this: $mixedBag = array("cat", 42, 8.5, false); How can this be represented in C++ code? One option would be to use void pointers (or the superior version, boost::any), but then you need to cast when you take stuff back out of the array... and I'm not at all convinced that the type inferencer can always figure out what to cast to at the other end. A better option, perhaps, would be something more like a union (or boost::variant), but then you need to enumerate all possible types at compile time... maybe possible, but certainly messy since arrays can contain arbitrarily complex entities. Does anyone know how HipHop and similar tools which go from a dynamic typing discipline to a static discipline handle these types of problems?

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Google Chrome Application Mode: Possible to isolate multiple instances?

- by Jonathan Eunice

I want to run multiple Google Chrome application windows logged into the same web site (Twitter.com, say), each with different credentials. Is this possible? If so, how? My initial testing shows that multiple Chrome app windows are not sufficiently isolated to do this. Logging into the second account logs me into the second account in both windows, suggesting that they are sharing information just as two Chrome tabs might.

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What is the complexity of this c function

- by Bunny Rabbit

what is the complexity of the following c Function ? double foo (int n) { int i; double sum; if (n==0) return 1.0; else { sum = 0.0; for (i =0; i<n; i++) sum +=foo(i); return sum; } } Please don't just post the complexity can you help me in understanding how to go about it . EDIT: It was an objective question asked in an exam and the Options provided were 1.O(1) 2.O(n) 3.O(n!) 4.O(n^n)

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