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• Is there a name for the technique of using base-2 numbers to encode a list of unique options?

  - by Lunatik

  Apologies for the rather vague nature of this question, I've never been taught programming and Google is rather useless to a self-help guy like me in this case as the key words are pretty ambiguous. I am writing a couple of functions that encode and decode a list of options into a Long so they can easily be passed around the application, you know this kind of thing: 1 - Apple 2 - Orange 4 - Banana 8 - Plum etc. In this case the number 11 would represent Apple, Orange & Plum. I've got it working but I see this used all the time so assume there is a common name for the technique, and no doubt all sorts of best practice and clever algorithms that are at the moment just out of my reach.

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• When is it appropriate to use C++ exceptions?

  - by krebstar

  I'm trying to design a class that needs to dynamically allocate some memory.. I had planned to allocate the memory it needs during construction, but how do I handle failed memory allocations? Should I throw an exception? I read somewhere that exceptions should only be used for "exceptional" cases, and running out of memory doesn't seem like an exceptional case to me.. Should I allocate memory in a separate initialization routine instead and check for failures and then destroy the class instance gracefully? Or should I use exceptions instead? The class won't have anything useful to do if these memory allocations should fail.. EDIT: The consensus seems to be that running out of memory IS an exceptional case. Will see how to go about this.. Thanks.. :)

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• How to null a translation in gettext system?

  - by Evgeny

  Suppose a simple phrase "In" in English needs to be interpreted as "" - empty string in Russian. Is is possible to specify that in the .po file? What normally happens if you set msgstr "" - you'll get the untranslated key, but I want to get nothing in that specific case. Here is a use case: I have underneath a giant search bar a set of buttons to select questions (for a Q&A site) from particular scopes - like so: (in English) In: [all] [unanswered] [my own] (in Russian I want) [???] [??? ???????] [???] It just sounds more natural. Yes I can leave out In for english, but I don't want to and I do not want to put button (things in [] are buttons) html into the 'po' file. Thanks!

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• What are the advantages to use StringBuilder versus XmlDocument or related to create XML documetns?

  - by Rob

  This might be a bit of a code smell, but I have seen it is some production code, namely the use of StringBuilder as opposed to XmlDocument when creating XML documents. In some cases these are write once operations (e.g. create the document and save it to disk) where as others are passing the built string to an XmlDocument to preform an XslTransform to a document that is returned to the client. So obvious question: is there merit to doing things this way, is it something that should be done on a case-by-case basis, or is this the wrong way of doing things?

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• Insert into a generic dictionary with possibility of duplicate keys?

  - by Chris Clark

  Is there any reason to favor one of these approaches over the other when inserting into a generic dictionary with the possibility of a key conflict? I'm building an in-memory version of a static collection so in the case of a conflict it doesn't matter whether the old or new value is used. If Not mySettings.ContainsKey(key) Then mySettings.Add(key, Value) End If Versus mySettings(key) = Value And then of course there is this, which is obviously not the right approach: Try mySettings.Add(key, Value) Catch End Try Clearly the big difference here is that the first and second approaches actually do different things, but in my case it doesn't matter. It seems that the second approach is cleaner, but I'm curious if any of you .net gurus have any deeper insight. Thanks!

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• Haskell: variant of `show` that doesn't wrap String and Char in quotes

  - by Joey Adams

  I'd like a variant of show (let's call it label) that acts just like show, except that it doesn't wrap Strings in " " or Chars in ' '. Examples: > label 5 "5" > label "hello" "hello" > label 'c' "c" I tried implementing this manually, but I ran into some walls. Here is what I tried: {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE UndecidableInstances #-} module Label where class (Show a) => Label a where label :: a -> String instance Label [Char] where label str = str instance Label Char where label c = [c] -- Default case instance Show a => Label a where label x = show x However, because the default case's class overlaps instance Label [Char] and instance Label Char, those types don't work with the label function. Is there a library function that provides this functionality? If not, is there a workaround to get the above code to work?

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• Element point map for html5 canvas element, need algorithm

  - by Artiom Chilaru

  I'm currently working on a pure html 5 canvas implementation of the "flying tag cloud sphere", which many of you have undoubtedly seen as a flash object in some pages. The tags are drawn fine, and the performance is satisfactory, but there's one thing in the canvas element that's kind of breaking this idea: you can't identify the objects that you've drawn on a canvas, as it's just a simple flat "image".. What I have to do in this case is catch the click event, and try to "guess" which element was clicked. So I have to have some kind of matrix, which stores a link to a tag object for each pixel on the canvas, AND I have to update this matrix on every redraw. Now this sounds incredibly inefficient, and before I even start trying to implement this, I want to ask the community - is there some "well known" algorithm that would help me in this case? Or maybe I'm just missing something, and the answer is right behind the corner? :)

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• How to salvage SQL server 2008 query from KILLED/ROLLBACK state without waiting half a day?

  - by littlegreen

  I have a stored procedure that inserts batches of millions of rows, emerging from a certain query, into an SQL database. It has one parameter selecting the batch; when this parameter is omitted, it will gather a list of batches and recursively call itself, in order to iterate over batches. In (pseudo-)code, it looks something like this: CREATE PROCEDURE spProcedure AS BEGIN IF @code = 0 BEGIN ... WHILE @@Fetch_Status=0 BEGIN EXEC spProcedure @code FETCH NEXT ... INTO @code END END ELSE BEGIN -- Disable indexes ... INSERT INTO table SELECT (...) -- Enable indexes ... Now it can happen that this procedure is slow, for whatever reason: it can't get a lock, one of the indexes it uses is misdefined or disabled. In that case, I want to be able kill the procedure, truncate and recreate the resulting table, and try again. However, when I try and kill the procedure, the process frequently oozes into a KILLED/ROLLBACK state from which there seems to be no return. From Google I have learned to do an sp_lock, find the spid, and then kill it with KILL <spid>. But when I try to kill it, it tells me SPID 75: transaction rollback in progress. Estimated rollback completion: 0%. Estimated time remaining: 554 seconds. I did find a forum message hinting that another spid should be killed before the other one can start a rollback. But that didn't work for me either, plus I do not understand, why that would be the case... could it be because I am recursively calling my own stored procedure? (But it should be having the same spid, right?) In any case, my process is just sitting there, being dead, not responding to kills, and locking the table. This is very frustrating, as I want to go on developing my queries, not waiting hours on my server sitting dead while pretending to be finishing a supposed rollback. Is there some way in which I can tell the server not to store any rollback information for my query? Or not to allow any other queries to interfere with the rollback, so that it will not take so long? Or how to rewrite my query in a better way, or how kill the process successfully without restarting the server?

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• C++ Long switch statement or look up with a map?

  - by Rachel

  In my C++ application, I have some values that act as codes to represent other values. To translate the codes, I've been debating between using a switch statement or an stl map. The switch would look something like this: int code; int value; switch(code) { case 1: value = 10; break; case 2: value = 15; break; } The map would be an stl::map<int, int> and translation would be a simple lookup with the code used as the key value. Which one is better/more efficient/cleaner/accepted? Why?

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• why is there different id syntax in the Android docs?

  - by darren

  This page in the Android documentation defines an element id as follows: <TextView android:id="@+id/label" android:layout_width="fill_parent" android:layout_height="wrap_content" android:text="Type here:" /> However this page defines it as: <EditText id="text" xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:textColor="@color/opaque_red" android:text="Hello, World!" /> I thought I had a decent understanding of what was going on until I saw this second example. In the first case, you need the + character so that id 'label' is added to the R file, correct? In the second case, would the EditText's id not be added to the R file because it does not contain the + character? Also, the second example does not include the android namespace on the id. Does having or not having the Android namespace affect whether that id will be added to the R file? Thanks for any clarification.

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• What's the performance penalty of weak_ptr?

  - by Kornel Kisielewicz

  I'm currently designing a object structure for a game, and the most natural organization in my case became a tree. Being a great fan of smart pointers I use shared_ptr's exclusively. However, in this case, the children in the tree will need access to it's parent (example -- beings on map need to be able to access map data -- ergo the data of their parents. The direction of owning is of course that a map owns it's beings, so holds shared pointers to them. To access the map data from within a being we however need a pointer to the parent -- the smart pointer way is to use a reference, ergo a weak_ptr. However, I once read that locking a weak_ptr is a expensive operation -- maybe that's not true anymore -- but considering that the weak_ptr will be locked very often, I'm concerned that this design is doomed with poor performance. Hence the question: What is the performance penalty of locking a weak_ptr? How significant is it?

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• Feature categories for a social network

  - by mafutrct

  Not sure if this question belongs on SO. Anyway, please let me try to clarify the issue. I'm currently planning a social program. It's basically a chat server with the major additional ability to play games. I'd like to create categories of features that are offered to users. My question is, are there any useful standard feature categories? Does not have to be specific to my case, I'm interested in the general case as well. Just to give you an idea of what I'm thinking: functional e.g. play games social e.g. chatting operational e.g. 24/7 service availability I'm entirely unsure if this is the right place to ask, if you know of any better site to ask please don't hesitate to add a comment.

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• Programming languages: out of the box legibility and extensibility

  - by sova

  Two excellent results of SOLID development ideology are - Legibility - Extensibility over the life of a project (http://en.m.wikipedia.org/wiki/Solid_(object-oriented_design) Although SOLID is a set of language-agnostic design ideas, some languages inherently support these ideas better than others. Out-of-the-box or after various customizations, in your opinion which language is best-suited to be both easily readable and easy to extend functionality in? Some definitions to pre-empt biases and flamewars: Legibility: amount of thinking done to understand the code proportional to the amount of code: (amount_think-energy / amount_code) is fairly constant and as low as possible in the optimal case. Extensibility: Addition of X amount of functionality requires a change in code or code additions in proportion to X (amount_added_functionality / amount_added_code) is fairly constant and as high as possible in the optimal case. Supporting information and tutorials encouraged. Code snippets welcome.

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• How do I handle the Maybe result of at in Control.Lens.Indexed without a Monoid instance

  - by Matthias Hörmann

  I recently discovered the lens package on Hackage and have been trying to make use of it now in a small test project that might turn into a MUD/MUSH server one very distant day if I keep working on it. Here is a minimized version of my code illustrating the problem I am facing right now with the at lenses used to access Key/Value containers (Data.Map.Strict in my case) {-# LANGUAGE OverloadedStrings, GeneralizedNewtypeDeriving, TemplateHaskell #-} module World where import Control.Applicative ((<$>),(<*>), pure) import Control.Lens import Data.Map.Strict (Map) import qualified Data.Map.Strict as DM import Data.Maybe import Data.UUID import Data.Text (Text) import qualified Data.Text as T import System.Random (Random, randomIO) newtype RoomId = RoomId UUID deriving (Eq, Ord, Show, Read, Random) newtype PlayerId = PlayerId UUID deriving (Eq, Ord, Show, Read, Random) data Room = Room { _roomId :: RoomId , _roomName :: Text , _roomDescription :: Text , _roomPlayers :: [PlayerId] } deriving (Eq, Ord, Show, Read) makeLenses ''Room data Player = Player { _playerId :: PlayerId , _playerDisplayName :: Text , _playerLocation :: RoomId } deriving (Eq, Ord, Show, Read) makeLenses ''Player data World = World { _worldRooms :: Map RoomId Room , _worldPlayers :: Map PlayerId Player } deriving (Eq, Ord, Show, Read) makeLenses ''World mkWorld :: IO World mkWorld = do r1 <- Room <$> randomIO <*> (pure "The Singularity") <*> (pure "You are standing in the only place in the whole world") <*> (pure []) p1 <- Player <$> randomIO <*> (pure "testplayer1") <*> (pure $ r1^.roomId) let rooms = at (r1^.roomId) ?~ (set roomPlayers [p1^.playerId] r1) $ DM.empty players = at (p1^.playerId) ?~ p1 $ DM.empty in do return $ World rooms players viewPlayerLocation :: World -> PlayerId -> RoomId viewPlayerLocation world playerId= view (worldPlayers.at playerId.traverse.playerLocation) world Since rooms, players and similar objects are referenced all over the code I store them in my World state type as maps of Ids (newtyped UUIDs) to their data objects. To retrieve those with lenses I need to handle the Maybe returned by the at lens (in case the key is not in the map this is Nothing) somehow. In my last line I tried to do this via traverse which does typecheck as long as the final result is an instance of Monoid but this is not generally the case. Right here it is not because playerLocation returns a RoomId which has no Monoid instance. No instance for (Data.Monoid.Monoid RoomId) arising from a use of `traverse' Possible fix: add an instance declaration for (Data.Monoid.Monoid RoomId) In the first argument of `(.)', namely `traverse' In the second argument of `(.)', namely `traverse . playerLocation' In the second argument of `(.)', namely `at playerId . traverse . playerLocation' Since the Monoid is required by traverse only because traverse generalizes to containers of sizes greater than one I was now wondering if there is a better way to handle this that does not require semantically nonsensical Monoid instances on all types possibly contained in one my objects I want to store in the map. Or maybe I misunderstood the issue here completely and I need to use a completely different bit of the rather large lens package?

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• UITableView: Mixing static and dynamic cells

  - by AlexR

  I am trying to mix dynamic and static cells in a grouped table view: I would like to get two sections with static cells at the top followed by a section of dynamic cells (please refer to the screenshot below). I have set the table view contents to static cells. I designed the static cells in Interface Builder and gave them identifiers related to their section and row: "section0static0", "section0static1", "section1static0" and "section1static1". I named the dynamic cell "section2dynamic". My delegate methods, in which I am trying to return the correct cell identifier (static or dynamic) are as follows: - (NSInteger)tableView:(UITableView *)tableView numberOfRowsInSection:(NSInteger)section { switch (section) { case 0: return 2; break; case 1: return 2; break; case 2: return 0; break; default: break; } return 0; } - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @""; if (indexPath.section <= 1) CellIdentifier = [NSString stringWithFormat:@"section%istatic%i",indexPath.section,indexPath.row]; else CellIdentifier = [NSString stringWithFormat:@"section%idynamic",indexPath.section]; UITableViewCell *cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath]; return cell; } Edit Based on AppleFreak's advice I have changed my code as follows: - (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath { static NSString *CellIdentifier = @"Cell"; UITableViewCell *cell; if (indexPath.section <= 1) { // section <= 1 indicates static cells cell = [super tableView:tableView cellForRowAtIndexPath:indexPath]; } else { // section > 1 indicates dynamic cells CellIdentifier = [NSString stringWithFormat:@"section%idynamic",indexPath.section]; cell = [tableView dequeueReusableCellWithIdentifier:CellIdentifier forIndexPath:indexPath]; } return cell; } However, my app crashes with error message Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'UITableView dataSource must return a cell from tableView:cellForRowAtIndexPath:' for section 0 and row 0. The cell returned from cell = [super tableView:tableView cellForRowAtIndexPath:indexPath] for section 0 and row 0 is nil. What is wrong with my code? Could there be any problems with my outlets? I haven't set any outlets because I am subclassing UITableViewController and supposedly do not any outlets for tableview to be set (?). Any suggestions on how to better do it?

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• How do you write an idiomatic Scala Quicksort function?

  - by Don Mackenzie

  I recently answered a question with an attempt at writing a quicksort function in scala, I'd seen something like the code below written somewhere. def qsort(l: List[Int]): List[Int] = { l match { case Nil => Nil case pivot::tail => qsort(tail.filter(_ < pivot)) ::: pivot :: qsort(tail.filter(_ >= pivot)) } } My answer received some constructive criticism pointing out that List was a poor choice of collection for quicksort and secondly that the above wasn't tail recursive. I tried to re-write the above in a tail recursive manner but didn't have much luck. Is it possible to write a tail recursive quicksort? or, if not, how can it be done in a functional style? Also what can be done to maximise the efficiency of the implementation? Thanks in advance.

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• Open an Application .exe window inside another application

  - by jpnavarini

  I have an application in WPF running. I would like that, when a button is clicked inside this application, another application opens, with its window maximized. However, I don't want my first application to stop and wait. I want both to be open and running independently. When the button is clicked again, in case the application is minimized, the application is maximized. In case it is not, it is open again. How is it possible using C#? I have tried the following: Process process = Process.GetProcesses().FirstOrDefault(f => f.ProcessName.Contains("Analysis")); ShowWindow((process ?? Process.Start("..\\..\\..\\MS Analysis\\bin\\Debug\\Chemtech.RT.MS.Analysis.exe")).MainWindowHandle.ToInt32(), SW_MAXIMIZE); But the window does not open, even though the process does start.

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• Scala: Matching optional Regular Expression groups

  - by Brian Heylin

  I'm trying to match on an option group in Scala 2.8 (beta 1) with the following code: import scala.xml._ val StatementPattern = """([\w\.]+)\s*:\s*([+-])?(\d+)""".r def buildProperty(input: String): Node = input match { case StatementPattern(name, value) => <propertyWithoutSign /> case StatementPattern(name, sign, value) => <propertyWithSign /> } val withSign = "property.name: +10" val withoutSign = "property.name: 10" buildProperty(withSign) // <propertyWithSign></propertyWithSign> buildProperty(withoutSign) // <propertyWithSign></propertyWithSign> But this is not working. What is the correct way to match optional regex groups?

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• Should class IOException in Java have been an unchecked RuntimeException?

  - by Derek Mahar

  Do you agree that the designers of Java class java.io.IOException should have made it an unchecked run-time exception derived from java.lang.RuntimeException instead of a checked exception derived only from java.lang.Exception? I think that class IOException should have been an unchecked exception because there is little that an application can do to resolve problems like file system errors. However, in When You Can't Throw An Exception, Elliotte Rusty Harold claims that most I/O errors are transient and so you can retry an I/O operation several times before giving up: For instance, an IOComparator might not take an I/O error lying down, but — because many I/O problems are transient — you can retry a few times, as shown in Listing 7: Is this generally the case? Can a Java application correct I/O errors or wait for the system to recover? If so, then it is reasonable for IOException to be checked, but if it is not the case, then IOException should be unchecked so that business logic can delegate handling of this exception to a separate system error handler.

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• Transition between many Views in ViewFlipper ?

  - by user164589

  Hi guys, I am using "ViewFlipper" for my application. This ViewFlipper includes 5 layouts. I am trying make it that can be changed from current layout to any layout. In other words, it can be changed Layout#1 - Layout#5 or Layout#4 - Layout#1 ..etc. How to make it ? I used showNext() and showPrevious(). It is not better idea for my case. Can I use ViewSwither instead of this case ? Please advice. Can you give example code related this issue ? Thanks in advance.

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• JSF: attach rich:toggleControl to radio buttons or select items.

  - by arw

  Has anyone had any success attaching a rich:toggleControl component to a radio button component (h:selectOneRadio) or alternatively any of its children select items (in this case s:enumItem). Basic code example: <h:selectOneRadio value="#{backingValue}"> <s:enumItem enumValue="VAL_1" itemLabel="Value One" /> <s:enumItem enumValue="VAL_2" itemLabel="Value Two" /> <s:convertEnum /> </h:selectOneRadio> The ideal thing would be to attach the toggle control to the enumItems so I could have it switch to a particular state. However at this point I'd be happy if the toggle control can just be attached to the selectOneRadio. I've tried the toggle control as a child of the selectOneRadio and enumItems; neither works. I've also tried wrapping the toggleControl around the selectOneRadio, the toggle control works in this case but the radio buttons don't :(

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• Prototype and jQuery concatenation failure

  - by Corey Hart

  I found something strange when trying to concatenate prototype and jQuery. It seems as though when concatenated, the $ jquery reference doesn't get overwritten by prototype. I've built two test cases to single this out, and it's failing in Chrome8 and FF 3.6. Test Case 1 - Without Concatenation jQuery and Prototype are loaded separately with different script tags. jQuery is loaded first, Prototype second. Test Case 2 - With Concatenation jQuery and Prototype are concatenated into a single file, and loaded with a single script tag. jQuery is first in the script, and prototype is added second. These should act identically, but the second test is throwing errors because the $ function in prototype doesn't overwrite the $ jquery reference. Did I set these up wrong, or are browsers rendering javascript differently when it's all in the same file?

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• Detecting regular expression in content during parse

  - by sonofdelphi

  I am writing a parser for C. I was just running it with some other language files (for fun, to see the extent C-likeness). It breaks down if the code being parsed contains regular expressions... Case 1: For example, while parsing the JavaScript code snippet, var phone="(304)434-5454" phone=phone.replace(/[\(\)-]/g, "") //Returns "3044345454" (removes "(", ")", and "-") The '(', '[' etc get matched as starters of new scopes, which may never be closed. Case 2: And, for the Perl code snippet, # Replace backslashes with two forward slashes # Any character can be used to delimit the regex $FILE_PATH =~ s@\\@//@g; The // gets matched as a comment... How can I detect a regular expression within the content text of a "C-like" program-file?

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• How to allow sorting in the Django admin by a custom list_display field, which doesn't have a DB fie

  - by Gj

  I have a custom list_display field which is responsible for a column of integers in one of my admin pages. I need to allow staff members to sort according to it. There's a solution for how to acheive that if the integer represents a count/average/etc of some DB field, which is not the case for me. [ the solution for that case is here: http://stackoverflow.com/questions/2168475/django-admin-how-to-sort-by-one-of-the-custom-list-display-fields-that-has-no-da ] Any ideas how I can achieve this sorting without actually creating and maintaining a DB field for the values?

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• database change after pressing 'X' button

  - by Anup Prakash

  What i know:- We can use Ajax to change database from javascript. So whenever we press the 'X' button on title bar it calls "onbeforeunload" event. And by this event we can change the database. But in my case, i want to change the status of user only when user click on 'X' button. Not in case of changing the page. As because changing the page is unloading the page. and closing the page is also unloading the page(As much i know). Is there any way to differentiate between closing the page and moving from one page to other page? I want to use it for changing the status of user(i.e. login/logout), whenever he presses cross button. I don't want to set status "logout" when user changes the page. I want to set status "logout" when user 'X' the button. Plese help me.

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