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• Can hash tables really be O(1)

  - by drawnonward

  It seems to be common knowledge that hash tables can achieve O(1) but that has never made sense to me. Can someone please explain it? A. The value is an int smaller than the size of the hash table, so the value is its own hash, so there is no hash table but if there was it would be O(1) and still be inefficient. B. You have to calculate the hash, so the order is O(n) for the size of the data being looked up. The lookup might be O(1) after you do O(n) work, but that still comes out to O(n) in my eyes. And unless you have a perfect hash or a large hash table there are probably several items per bucket so it devolves into a small linear search at some point anyway. I think hash tables are awesome, but I do not get the O(1) designation unless it is just supposed to be theoretical.

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• About Attributes member of LUID_AND_ATTRIBUTES used in TOKEN_PRIVILEGES structure

  - by Astaroth

  MSDN article, Enabling and Disabling Privileges in C++, provided the a code example to show how to enable or disable a privilege in an access token. I quote the part in questioned: tp.PrivilegeCount = 1; tp.Privileges[0].Luid = luid; if (bEnablePrivilege) tp.Privileges[0].Attributes = SE_PRIVILEGE_ENABLED; else tp.Privileges[0].Attributes = 0; What is the meaning of zero value for Attributes member? According to the documentation of TOKEN_PRIVILEGES structure, the attributes of a privilege can be a combination of the following values: SE_PRIVILEGE_ENABLED  (it is 0x00000002L in WinNT.h) SE_PRIVILEGE_ENABLED_BY_DEFAULT  (it is 0x00000001L in WinNT.h) SE_PRIVILEGE_REMOVED  (it is 0x00000004L in WinNT.h) SE_PRIVILEGE_USED_FOR_ACCESS  (it is 0x80000000L in WinNT.h) So, we don't see any valid constant with a value of zero. I guess, the zero is equal to SE_PRIVILEGE_REMOVED. Anybody here could explain what the zero value really does?

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• Which of these Array Initializations is better in Ruby?

  - by Bragaadeesh

  Hi, Which of these two forms of Array Initialization is better in Ruby? Method 1: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = Array.new(DAYS_IN_A_WEEK.size).map!{ Array.new(HOURS_IN_A_DAY.size) } DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day][hour] = 'something' end end Method 2: DAYS_IN_A_WEEK = (0..6).to_a HOURS_IN_A_DAY = (0..23).to_a @data = {} DAYS_IN_A_WEEK.each do |day| HOURS_IN_A_DAY.each do |hour| @data[day] ||= {} @data[day][hour] = 'something' end end The difference between the first method and the second method is that the second one does not allocate memory initially. I feel the second one is a bit inferior when it comes to performance due to the numerous amount of Array copies that has to happen. However, it is not straight forward in Ruby to find what is happening. So, if someone can explain me which is better, it would be really great! Thanks

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• Alert Box Running First?

  - by corymathews

  I have some jQuery/JS below. The first thing to run is the alert box at the end. $(document).ready(function() { $("#id1 img , .msg").stop().animate( { width: '300px', height: '300px'}, { duration: 'slow', easing: 'easeInSine' }).pause(3000); $(".msg").animate( { width: '50px', height: '50px' }, { duration: 498, easing: 'easeOutSine' }); $("#id1 img").animate( { width: '50px', height: '50px' }, { duration: 500, easing: 'easeOutSine' }); $("#id1 img , .msg").animate( { width: '300px',height: '300px'}, { duration: 'slow', easing: 'easeInSine' }).pause(3000); alert('eh?'); }); I do have a easing plugin. If I run this the alert will show, and then the first animate will happen in the background but not be shown. It will just appear at the final size. Shouldn't the alert run at the end of all the animation? Can anyone explain why this is happening?

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• Can I use a single pointer for my hash table in C?

  - by aks

  I want to implement a hash table in the following manner: struct list { char *string; struct list *next; }; struct hash_table { int size; /* the size of the table */ struct list **table; /* the table elements */ }; Instead of struct hash_table like above, can I use: struct hash_table { int size; /* the size of the table */ struct list *table; /* the table elements */ }; That is, can I just use a single pointer instead of a double pointer for the hash table elements? If yes, please explain the difference in the way the elements will be stored in the table?

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• Threads in JAVA

  - by theband

  I was today asked in an interview over the Thread concepts in JAVA? The Questions were... What is a thread? Why do we go for threading? A real time example over the threads. Can we create threads in Spring framework service class. Can flex call a thread? I did not answer any questions apart from definition of Thread, that too i just learnt from internet. Can anyone explain me clearly over this.

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• Eclipse debug - line: not available

  - by Mike

  I can't seem to find anything on google telling me why this might be and what the resolution is. I'm Stepping through third party code (that I have the source for) and would really like to see the current line being executed... Looking at javac compile flags, I see the -g:none flag. If this flag is set, would this be enough to explain why I'm not able to see line numbers? If so, why would someone do this, are there performance implications? Do I need to recompile the jar myself to attach the missing debug info (if possible)? Thanks!

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• Graphics Question: How do I restrict the mouse cursor to within a circle?

  - by Dan

  I'm playing with XNA. When I click the left mouse button, I record the X,Y co-ordinates. Keeping the mouse button held down, moving the mouse draws a line from this origin to the current mouse position. I've offset this into the middle of the window. Now, what I'd like to do is restrict the mouse cursor to within a circle (with a radius of N, centred on the middle of the screen). Restricting the mouse to a rectangular region is easy enough (by adjusting the origin by the difference of the mouse position and the size of the region), but I haven't a clue on how to start doing it for a circular region. Can anyone explain how to do this? Any advice on where to start would be helpful.

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• Performance problem on a query.

  - by yapiskan

  Hi, I have a performance problem on a query. First table is a Customer table which has millions records in it. Customer table has a column of email address and some other information about customer. Second table is a CommunicationInfo table which contains just Email addresses. And What I want in here is; how many times the email address in CommunicationInfo table repeats in Customers table. What could be the the most performer query. The basic query that I can explain this situation is; Select ci.Email, count(*) from Customer c left join CommunicationInfo ci on c.Email1 = ci.Email or c.Email2 = ci.Email Group by ci.Email But sure, it takes about 5, 6 minutes in execution. Thanks in Advance.

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• Problem building relationships between models

  - by Brian Roisentul

  Until now, I've been using acts_as_taggable_on plugin for tagging announcements. That plugin creates the following tables: taggings: relates tags and announcements table(for the tagged item, it has a field called taggable_id, which I rename to "announcement_id" for what I'll explain below). tags: has the tag ids and names. The other day, I discovered that I had no way of getting the announcements tagged with a certain tag, but doing Announcement.tagged_with(tag_name), and I don't want to search by name, but for id. So, as I'm using almost nothing of the functionality in that plugin, I decided to create the models for taggings and tags tables, to accomplish this: Announcement.tags. The models' relationships look as following: class Tagging < ActiveRecord::Base belongs_to :announcement belongs_to :tag end class Tag < ActiveRecord::Base has_many :announcements, :through => :taggings end class Announcement < ActiveRecord::Base has_many :tags, :through => :taggings Why can't I execute the command Announcement.tags? Because when I try, I get undefined method `tags'

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• What is this VB6 method doing?

  - by Craig

  We are converting a VB6 application to C# (4.0). and have come across a method in VB6 that we're battling to understand. Public Sub SaveToField(fldAttach As ADODB.Field) Dim bData() As Byte Dim nSize As Long nSize = Len(m_sEmail) bData = LngToByteArray(nSize) fldAttach.AppendChunk bData If nSize > 0 Then bData = StringToByteArray(m_sEmail) fldAttach.AppendChunk bData End If nSize = Len(m_sName) bData = LngToByteArray(nSize) fldAttach.AppendChunk bData If nSize > 0 Then bData = StringToByteArray(m_sName) fldAttach.AppendChunk bData End If bData = LngToByteArray(m_nContactID) fldAttach.AppendChunk bData End Sub It seems like it's doing some binary file copy type thing, but I'm not quite understanding. Could someone explain so that we can rewrite it?

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• Problem with "not declared in this scope" error

  - by lego69

  I've got: error a1 was not declared in this scope Can somebody please explain why this code causes that? quiz.h #ifndef QUIZ_H_ #define QUIZ_H_ #include "quiz.cpp" class A { private: int player; public: A(int initPlayer); ~A(); void foo(); }; #endif /* QUIZ_H_ */ quiz.cpp #include "quiz.h" #include <iostream> using std::cout; using std::endl; A::A(int initPlayer = 0){ player = initPlayer; } A::~A(){ } void A::foo(){ cout << player; } main function #include "quiz.h" int main() { quiz(7); return 0; } quiz function #include "quiz.h" void quiz(int i) { A a1(i); a1.foo(); }

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• question about copy constructor

  - by lego69

  I have this class: class A { private: int player; public: A(int initPlayer = 0); A(const A&); A& operator=(const A&); ~A(); void foo() const; }; and I have function which contains this row: A *pa1 = new A(a2); can somebody please explain what exactly is going on, when I call A(a2) compiler calls copy constructor or constructor, thanks in advance

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• Java Thread wait() => blocked?

  - by Chris

  According to http://java.sun.com/j2se/1.5.0/docs/api/java/lang/Thread.State.html calling wait() will result a thread to go in BLOCKED state. However this piece of code will result (after being called) in a Thread in WAITING State. class bThread extends Thread { public synchronized void run() { try { wait(); } catch (InterruptedException e) { e.printStackTrace(); } } } Have I got something wrong? Can anybody explain this behaviour to me? Any help would be appreciated!

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• Suspension of Gmail account [closed]

  - by Ifeanyi Agu

  I have a Joomla site with my gmail account (google apps) being used as the SMTP server for sending mails. I also have a newsletter component on this site. I tried sending newsletter to all my subscribers and I noticed that the SMTP server could not be connected to. I then checked the emails of my company and noticed that the one I used to set it up was suspended. I cannot really explain why Google suspended the email account. Please could anyone tell me if Google saw the mails that were being sent as spam.

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• Property and Encapsulation

  - by Lijo

  Hi Team, Following is a question regarding using Properties in class. I am software engineer with 3 years of experience. I have been using public properties instead of exposing member variables publically. Many a people told that this approach helps in encapsulation. I don’t realize any encapsulation advantage by making it a property. While discussions, I came to know that not many people knows about the real reason for going for Property. They just do it as part of coding standard. Can someone clearly explain how Property is better than public member variable? How it improves encapsulation? Thanks Lijo

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• What is this PHP Syntax: ($variation_id>0) ? $variation_id : $item_id;

  - by user1325258

  Is someone able to explain the meaing of the following statment, and the type of php it is reffering to so I can do further research: $foo = ($variation_id>0) ? $variation_id : $item_id; I have tried search but don't really know what i'm searching for. What I am trying to find out is the name and meaning of the following syntax ? / : and is ($variation_id>0) just a shorthand if statement ? -- I just stumbled upon conditional variables although a nice simple explanation would still be appreciated.

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• PHP MySQL query string

  - by user1174762

  I am newer to PHP and MySQL and I am having trouble understanding join. I think, for me, the problem lies with actually understanding the logic of the query. What I am trying to do Is select all of the status updates from a table named "post", but only ones from users I am "following", and then display them In order by date. So, I have two databases which are set up like so: posts |post_id|user_id|post_body|date_upload| | 1 | 4 | hey. | 01/2/2012 | follows |relation_id|user_id|followee_id| | 1 | 4 | 2 | Could someone please explain how I should syntactically and Logically set this up? Thank you!

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• Is there an HTML code that can make my background picture transparent and my text non-transparent?

  - by user1831312

  Okay so I've been typing some HTML code for a technology class that I need to satisfy for my Education major. This is what i have for my background: body { background-image:url('islandbeach.jpg'); background-repeat:repeat; background-position:center; background-attachment:fixed; background-size:cover; } Now, I want to make my background transparent or faded so I can see the text and the other image that I have. The background is too colorful to be able to see the words without having to squint. Are there any HTML codes that can do this for me? I am not a pro at this stuff, I've just been following everything my professor has told me to do so please explain stuff in baby steps if you do have an answer. Thank you so so much!

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• iPhone App on iPad - What is the extra effort?

  - by hol

  I started to develop an iPhone App for a client but the binary not yet submitted to Apple. My client asked me whether they can run the iPhone App also on the iPad. I am not sure what to answer. I am away from home and cannot even check how this all works in XCode. I wonder whether I have to submit two binaries two Apple - one for iPhone and one for iPad - or how this all works? If somebody with experience can explain me. Basically I need to figure out how much more effort I have to consider if it is only making the app work on the iPad. I do not mean the effort to redesign the whole app being a real "iPad app". Just to make it work and when somebody downloads the app and it can be for an iPhone and for an iPad and it does not matter.

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• Python and object/class attrs - what's going on?

  - by digitala

  Can someone explain why Python does the following? >>> class Foo(object): ... bar = [] ... >>> a = Foo() >>> b = Foo() >>> a.bar.append(1) >>> b.bar [1] >>> a.bar = 1 >>> a.bar 1 >>> b.bar [1] >>> a.bar = [] >>> a.bar [] >>> b.bar [1] >>> del a.bar >>> a.bar [1] It's rather confusing!

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• *(char**) how to understand this construct?

  - by House.Lee

  recently, while reading former's code in my current project, I encounter the problems below: while implementing the Queue, my former wrote codes like this: while(uq->pHead) { char *tmp = uq->pHead; uq->pHead = *(char **)tmp; //... } the uq-pHead has definition like: typedef struct { char* pHead; //... } Queue; Well, I'm quite confused about the usage that "uq->pHead = *(char**)tmp" , could anyone explain it to me in detail? if we assume that *(uq-pHead) = 32(i.e. ' ') , *(char**)tmp would translate this into pointer-form, but...how could it make sense? Thanks a lot.

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• Confusing calling method in Java

  - by vBx

  class Parent { private void method1() { System.out.println("Parent's method1()"); } public void method2() { System.out.println("Parent's method2()"); method1(); } } class Child extends Parent { public void method1() { System.out.println("Child's method1()"); } } class test { public static void main(String args[]) { Parent p = new Child(); p.method2(); } } I'm confuse why does in Parent::method2() when invoking method1() it will cal Parents method1() and not Childs method1 ? I see that this happens only when method1() is private? Can someone explain me why ? Thanks you.

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• C++ inheritance doubt

  - by Poiuyt

  Can you explain why this is not allowed, #include <stdio.h> class B { private: int a; public: int a; }; int main() { return 0; } while this is? #include <stdio.h> class A { public: int a; }; class B : public A{ private: int a; }; int main() { return 0; } In both the cases, we have one public and one private variable named a in class B.

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• Can typeid() be used to pass a function?

  - by Kerb_z

  I tried this and got the output as: void Please explain the following Code: #include <cstdio> #include <typeinfo> using namespace std ; void foo() { } int main(void) { printf("%s", typeid(foo()).name());// Please notice this line, is it same as typeid( ).name() ? return 0; } AFAIK: The typeid operator allows the type of an object to be determined at run time. So, does this sample code tell us that a function that returns void is of *type void*. I mean a function is a method and has no type. Correct?

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