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  • What are the lesser known but cool data structures ?

    - by f3lix
    There a some data structures around that are really cool but are unknown to most programmers. Which are they? Everybody knows linked lists, binary trees, and hashes, but what about Skip lists, Bloom filters for example. I would like to know more data structures that are not so common, but are worth knowing because they rely on great ideas and enrich a programmer's tool box. PS: I am also interested on techniques like Dancing links which make interesting use of the properties of a common data structure. EDIT: Please try to include links to pages describing the data structures in more detail. Also, try to add a couple of words on why a data structures is cool (as Jonas Kölker already pointed out). Also, try to provide one data-structure per answer. This will allow the better data structures to float to the top based on their votes alone.

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  • The Definition of Regular Languages

    - by AraK
    Good Day, I have tried, and burned my brain to understand the definition of Regular Languages in Discrete Mathematics and its Applications(Rosen) without reaching the goal of understanding why the definition is like that in this book. On page(789), I am rephrasing the definition: Type 3 grammars are defined as: w1 --> w2 Where w1 is a non-terminal, and w2 is of the form: w2 = aB w2 = a Where B is a non-terminal, and a is a terminal. A special case is when w1 is the starting symbol and w2 is lambda(the empty string): w1 = S S --> lambda Two questions I couldn't find an answer for. First, Why can't w2 be of the form Ba. Second, Why lambda is only allowed for the starting symbol only. The book states that, regular languages are equivalent to Finite State Automaton, and we can easily see that a we can build FSA for both cases. I took a look at other resources, and these restrictions don't exist in these resources. Thanks,

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  • Sharing storage between servers

    - by El Yobo
    I have a PHP based web application which is currently only using one webserver but will shortly be scaling up to another. In most regards this is pretty straightforward, but the application also stores a lot of files on the filesystem. It seems that there are many approaches to sharing the files between the two servers, from the very simple to the reasonably complex. These are the options that I'm aware of Simple network storage NFS SMB/CIFS Clustered filesystems Lustre GFS/GFS2 GlusterFS Hadoop DFS MogileFS What I want is for a file uploaded via one webserver be immediately available if accessed through the other. The data is extremely important and absolutely cannot be lost, so whatever is implemented needs to a) never lose data and b) have very high availability (as good as, or better, than a local filesystem). It seems like the clustered filesystems will also provide faster data access than local storage (for large files) but that isn't of vita importance at the moment. What would you recommend? Do you have any suggestions to add or anything specifically to look out for with the above options? Any suggestions on how to manage backup of data on the clustered filesystems?

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  • Humor in code

    - by pfranza
    When you are writing code or naming products, which sources of cultural references are you most likely to draw from? Which reference sources do you think are more likely to be universally understood? For example when findbugs sees that you've implemented equals() without overriding hashCode() it suggest that you implement it by returning 42 (a reference from HHGTTG) Or why we have big endian vs little endian encoding, referencing Gulliver's Travels Not that we should act unprofessionally with our code, but if you going to tell a person that they could only (watch/read/...) one (book/movie/show/...) which one would allow them to 'get' the most jokes?

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  • Swift CMutablePointers in factories e.g. NewMusicSequence

    - by Gene De Lisa
    How do you use C level factory methods in Swift? Let's try using a factory such as NewMusicSequence(). OSStatus status var sequence:MusicSequence status=NewMusicSequence(&sequence) This errors out with "error: variable 'sequence' passed by reference before being initialized". Set sequence to nil, and you get EXC_BAD_INSTRUCTION. You can try being explicit like this: var sp:CMutablePointer<MusicSequence>=nil status=NewMusicSequence(sp) But then you get a bad access exception when you set sp to nil. If you don't set sp, you get an "error: variable 'sp' used before being initialized" Here's the reference.

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  • Are there any protocols/standards on top of TCP optimized for high throughput and low latency?

    - by Nosrama
    Are there any protocols/standards that work over TCP that are optimized for high throughput and low latency? The only one I can think of is FAST. At the moment I have devised just a simple text-based protocol delimited by special characters. I'd like to adopt a protocol which is designed for fast transfer and supports perhaps compression and minification of the data that travels over the TCP socket.

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  • Vectorizing sums of different diagonals in a matrix

    - by reve_etrange
    I want to vectorize the following MATLAB code. I think it must be simple but I'm finding it confusing nevertheless. r = some constant less than m or n [m,n] = size(C); S = zeros(m-r,n-r); for i=1:m-r for j=1:n-r S(i,j) = sum(diag(C(i:i+r-1,j:j+r-1))); end end The code calculates a table of scores, S, for a dynamic programming algorithm, from another score table, C. The diagonal summing is to generate scores for individual pieces of the data used to generate C, for all possible pieces (of size r). Thanks in advance for any answers! Sorry if this one should be obvious...

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  • Is there an existing solution to the multithreaded data structure problem?

    - by thr
    I've had the need for a multi-threaded data structure that supports these claims: Allows multiple concurrent readers and writers Is sorted Is easy to reason about Fulfilling multiple readers and one writer is a lot easier, but I really would wan't to allow multiple writers. I've been doing research into this area, and I'm aware of ConcurrentSkipList (by Lea based on work by Fraser and Harris) as it's implemented in Java SE 6. I've also implemented my own version of a concurrent Skip List based on A Provably Correct Scalable Concurrent Skip List by Herlihy, Lev, Luchangco and Shavit. These two implementations are developed by people that are light years smarter then me, but I still (somewhat ashamed, because it is amazing work) have to ask the question if these are the two only viable implementations of a concurrent multi reader/writer data structures available today?

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  • How do I change careers to become a programmer with little money

    - by bgc83
    I'm currently a network engineer, but find myself wanting to get into the world of development. I took a little bit of Java in college, am 27 years old and have been network engineering for 4 years now. I have a mortgage and student loans so going back to school would be difficult. I'm willing to put in however much hardwork is needed around my full time job to learn, but part of me feels I may need actuall schooling to get down some of the advanced concepts. Just looking for a little advice and direction. I have purchased a bunch of the Head First programming books and have begun reading through some of them as I figure out my way into this transition.

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  • Regular expressions - finding and comparing the first instance of a word

    - by Dan
    Hi there, I am currently trying to write a regular expression to pull links out of a page I have. The problem is the links need to be pulled out only if the links have 'stock' for example. This is an outline of what I have code wise: <td class="prd-details"> <a href="somepage"> ... <span class="collect unavailable"> </td> <td class="prd-details"> <a href="somepage"> ... <span class="collect available"> </td> What I would like to do is pull out the links only if 'collect available' is in the tag. I have tried to do this with the regular expression: (?s)prd-details[^=]+="([^"]+)" .+?collect{1}[^\s]+ available However on running it, it will find the first 'prd-details' class and keep going until it finds 'collect available', thereby taking the incorrect results. I thought by specifying the {1} after the word collect it would only use the first instance of the word it finds, but apparently I'm wrong. I've been trying to use different things such as positive and negative lookaheads but I cant seem to get anything to work. Might anyone be able to help me with this issue? Thanks, Dan

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  • Debugging F# code and functional style

    - by Roger Alsing
    I'm new to funcctional programming and have some questions regarding coding style and debugging. I'm under the impression that one should avoid storing results from funcction calls in a temp variable and then return that variable e.g. let someFunc foo = let result = match foo with | x -> ... | y -> ... result And instead do it like this (I might be way off?): let someFunc foo = match foo with | x -> ... | y -> ... Which works fine from a functionallity perspective, but it makes it way harder to debug. I have no way to examine the result if the right hand side of - does some funky stuff. So how should I deal with this kind of scenarios?

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  • facing outsourced wages, can i still eat and survive as a computing science major ?

    - by wefwgeweg
    offshore outsourced programmers charge fraction of what costs a North American developer. should I still pursue my major as computing science ? Why would companies spend more on North American/local developers where they can get the same quality if not better job done offshore ? I am just concerned for the development labor market, the free market wants the lowest cost provider. not just programming but many high skilled labor such as engineering, scientists, artists and etc. perhaps i should become a lawyer ?

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  • What are the benefits of prototypal inheritance over classical?

    - by Pierreten
    So I finally stopped dragging my feet all these years and decided to learn JavaScript "properly". One of the most head-scratching elements of the languages design is it's implementation of inheritance. Having experience in Ruby, I was really happy to see closures and dynamic typing; but for the life of me can't figure out what benefits are to be had from object instances using other instances for inheritance.

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  • Code Golf: Rotating Maze

    - by trinithis
    Code Golf: Rotating Maze Make a program that takes in a file consisting of a maze. The maze has walls given by '#'. The maze must include a single ball, given by a 'o' and any number of holes given by a '@'. The maze file can either be entered via command line or read in as a line through standard input. Please specify which in your solution. Your program then does the following: 1: If the ball is not directly above a wall, drop it down to the nearest wall. 2: If the ball passes through a hole during step 1, remove the ball. 3: Display the maze. 4: If there is no ball in the maze, exit. 5: Read a line from the standard input. Given a 1, rotate the maze counterclockwise. Given a 2, rotate the maze clockwise. Rotations are done by 90 degrees. It is up to you to decide if extraneous whitespace is allowed. If the user enters other inputs, repeat this step. 6: Goto step 1. You may assume all input mazes are closed. Note, a hole effectively acts as a wall in this regard. You may assume all input mazes have no extraneous whitespace. The shortest source code by character count wins. Example mazes: ###### #o @# ###### ########### #o # # ####### # ###@ # ######### ########################### # # # # @ # # # # ## # # ####o#### # # # # # # ######### # @ ######################

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  • Is there a way to programatically check dependencies of an EXE?

    - by Mason Wheeler
    I've got a certain project that I build and distribute to users. I have two build configurations, Debug and Release. Debug, obviously, is for my use in debugging, but there's an additional wrinkle: the Debug configuration uses a special debugging memory manager, with a dependency on an external DLL. There's been a few times when I've accidentally built and distributed an installer package with the Debug configuration, and it's then failed to run once installed because the users don't have the special DLL. I'd like to be able to keep that from happening in the future. I know I can get the dependencies in a program by running Dependency Walker, but I'm looking for a way to do it programatically. Specifically, I have a way to run scripts while creating the installer, and I want something I can put in the installer script to check the program and see if it has a dependency on this DLL, and if so, cause the installer-creation process to fail with an error. I know how to create a simple CLI program that would take two filenames as parameters, and could run a DependsOn function and create output based on the result of it, but I don't know what to put in the DependsOn function. Does anyone know how I'd go about writing it?

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  • What should I call a class that contains a sequence of states

    - by Robert P
    I have a GUI tool that manages state sequences. One component is a class that contains a set of states, your typical DFA state machine. For now, I'll call this a StateSet. However, I have another class that has a collection (possibly partially unordered) of those state sets, and lists them in a particular order. and I'm trying to come up with a good name for it - not just for internal code, but for customers to refer to it. I've got: Sequence (maybe) StateSetSet (reasonable for code, but not for customers) Any other suggestions or ideas?

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  • Python script to calculate aded combinations from a dictionary

    - by dayde
    I am trying to write a script that will take a dictionary of items, each containing properties of values from 0 - 10, and add the various elements to select which combination of items achieve the desired totals. I also need the script to do this, using only items that have the same "slot" in common. For example: item_list = { 'item_1': {'slot': 'top', 'prop_a': 2, 'prop_b': 0, 'prop_c': 2, 'prop_d': 1 }, 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 }, 'item_3': {'slot': 'top', 'prop_a': 2, 'prop_b': 5, 'prop_c': 2, 'prop_d':-2 }, 'item_4': {'slot': 'mid', 'prop_a': 5, 'prop_b': 5, 'prop_c':-5, 'prop_d': 0 }, 'item_5': {'slot': 'mid', 'prop_a':10, 'prop_b': 0, 'prop_c':-5, 'prop_d': 0 }, 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 }, 'item_7': {'slot': 'bot', 'prop_a': 1, 'prop_b': 3, 'prop_c':-4, 'prop_d': 4 }, 'item_8': {'slot': 'bot', 'prop_a': 2, 'prop_b': 2, 'prop_c': 0, 'prop_d': 0 }, 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 }, } The script would then need to select which combinations from the "item_list" dict that using 1 item per "slot" that would achieve a desired result when added. For example, if the desired result was: 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0, the script would select 'item_2', 'item_6', and 'item_9', along with any other combination that worked. 'item_2': {'slot': 'top', 'prop_a': 5, 'prop_b': 0, 'prop_c': 1, 'prop_d':-1 } 'item_6': {'slot': 'mid', 'prop_a':-5, 'prop_b': 2, 'prop_c': 3, 'prop_d': 5 } 'item_9': {'slot': 'bot', 'prop_a': 3, 'prop_b': 1, 'prop_c': 4, 'prop_d':-4 } 'total': 'prop_a': 3, 'prop_b': 3, 'prop_c': 8, 'prop_d': 0 Any ideas how to accomplish this? It does not need to be in python, or even a thorough script, but just an explanation on how to do this in theory would be enough for me. I have tried working out looping through every combination, but that seems to very quickly get our of hand and unmanageable. The actual script will need to do this for about 1,000 items using 20 different "slots", each with 8 properties. Thanks for the help!

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  • Generating easy-to-remember random identifiers

    - by Carl Seleborg
    Hi all, As all developers do, we constantly deal with some kind of identifiers as part of our daily work. Most of the time, it's about bugs or support tickets. Our software, upon detecting a bug, creates a package that has a name formatted from a timestamp and a version number, which is a cheap way of creating reasonably unique identifiers to avoid mixing packages up. Example: "Bug Report 20101214 174856 6.4b2". My brain just isn't that good at remembering numbers. What I would love to have is a simple way of generating alpha-numeric identifiers that are easy to remember. Examples would be "azil3", "ulmops", "fel2way", etc. I just made these up, but they are much easier to recognize when you see many of them at once. I know of algorithms that perform trigram analysis on text (say you feed them a whole book in German) and that can generate strings that look and feel like German words. This requires lots of data, though, and makes it slightly less suitable for embedding in an application just for this purpose. Do you know of anything else? Thanks! Carl

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  • How should i organize authority code?

    - by acidzombie24
    I have users that fall into the following Not logged in Not Verified Verified Moderator Admin All code that only admin and moderators can access (like banning) is in ModeratorUser which inherits from verified which inherits from BaseUser. Some pages are accessible to all users such as public profiles. If a user is logged in he can leave a comment. To check this i use if (IsVerifiedUser). Now here is the problem. To avoid problems if a user is banned he is not recognized as a verified user. However in the rare case i need to know if he is verified i can use usertype & Verified. Should i not be doing this? I have a bunch of code in my VerifiedUser class and find i am moving tons of it to BaseUser. Is this something i help because a not logged in user can access the page? Should i handle the ban user in a different way and allow IsVerifiedUser to be true even if the user is banned?

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  • How To Read Data using Ip Address

    - by DATT OZA
    I am doing punch card reader programming.. Establish connection with BioAccess V2 Device... socket successdully connected but data can't read... so how to read data ? Socket sock = new Socket(AddressFamily.InterNetwork, SocketType.Stream,ProtocolType.Tcp); var ipaddress = IPAddress.Parse("192.168.000.111"); IPAddress add = new IPAddress(ipaddress.GetAddressBytes()); EndPoint ep = new IPEndPoint(add, 5005); sock.Connect(ep); if(sock.connected) { } now what i have to do in IF BLOCK to read data ?

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