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  • How to calculate order (big O) for more complex algorithms (ie quicksort)

    - by bangoker
    I know there are quite a bunch of questions about big O notation, I have already checked Plain english explanation of Big O , Big O, how do you calculate/approximate it?, and Big O Notation Homework--Code Fragment Algorithm Analysis?, to name a few. I know by "intuition" how to calculate it for n, n^2, n! and so, however I am completely lost on how to calculate it for algorithms that are log n , n log n, n log log n and so. What I mean is, I know that Quick Sort is n log n (on average).. but, why? Same thing for merge/comb, etc. Could anybody explain me in a not to math-y way how do you calculate this? The main reason is that Im about to have a big interview and I'm pretty sure they'll ask for this kind of stuff. I have researched for a few days now, and everybody seem to have either an explanation of why bubble sort is n^2 or the (for me) unreadable explanation a la wikipedia Thanks!

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  • Learning Algorithms and Data Structures Fundamentals

    - by valya
    Can you recommend me a book or (better!) a site with many hard problems and exercises about data structures? I'm already answering project Euler questions, but these questions are about interesting, but uncommon algorithms. I hardly used even a simple tree. Maybe there is a site with exercises like: hey, you need to calculate this: ... . Do it using a tree. Now do it using a zipper. Upload your C (Haskell, Lisp, even Pascal or Fortress go) solution. Oh, your solution is so slow! Self-education is very hard then you trying to learn very common, fundamental things. How can I help myself with them without attending to courses or whatever?

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  • Articles about replication schemes/algorithms?

    - by jkff
    I'm designing an hierarchical distributed system (every node has zero or more "master" nodes to which it propagates its current data). The data gets continuously updated and I'd like to guarantee that at least N nodes have almost-current data at any given time. I do not need complete consistency, only eventual consistency (t.i. for any time instant, the current snapshot of data should eventually appear on at least N nodes. It is tricky to define the term "current" here, but still). Nodes may fail and go back up at any moment, and there is no single "central" node. O overflowers! Point me to some good papers describing replication schemes. I've so far found one: Consistency Management in Optimistic Replication Algorithms

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  • Algorithms for modern hardware?

    - by Jurily
    Once again, I find myself with a set of broken assumptions. The article itself is about a 10x performance gain by modifying a proven-optimal algorithm to account for virtual memory: What good is an O(log2(n)) algorithm if those operations cause page faults and slow disk operations? For most relevant datasets an O(n) or even an O(n^2) algorithm, which avoids page faults, will run circles around it. Are there more such algorithms around? Should we re-examine all those fundamental building blocks of our education? What else do I need to watch out for when writing my own?

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  • Load balancing and shedulling algorithms .NET

    - by Lukas Šalkauskas
    Hello there, so here is my problem: I have several different configuarion servers. I have different calculations (jobs), I can predict how long approx. each job will take to be caclulated. Also I have priorities. My question is how to keep all machines loaded 99-100% and shedule the jobs in the best way. Each machine can do several calculations at the time. Jobs are pushed to the machine. Central machine knows current load of each machine. Also I would like to to assign some king of machine learning here, because I will know statistics of each job (started, finished, cpu load etc.). How to distribute jobs(calculations) in the best possible way, also keep in mind priority. Any suggestions ? Ideas ? Algorithms ?

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  • Writing shorter code/algorithms, is more efficient (performance)?

    - by Carlos
    After coming across the code golf trivia around the site it is obvious people try to find ways to write code and algorithms as short as the possibly can in terms of characters, lines and total size, even if that means writing something like: n=input() while n>1:n=(n/2,n*3+1)[n%2];print n So as a beginner I start to wonder whether size actually matters :D. It is obviously a very subjective question highly dependent on the actual code being used, but what is the rule of thumb in the real world. In the case that size wont matter, how come then we don't focus more on performance rather than size?

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  • Load balancing and scheduling algorithms.

    - by Lukas Šalkauskas
    Hello there, so here is my problem: I have several different configuarion servers. I have different calculations (jobs); I can predict how long approximately each job will take to be caclulated. Also, I have priorities. My question is how to keep all machines loaded 99-100% and schedule the jobs in the best way. Each machine can do several calculations at a time. Jobs are pushed to the machine. The central machine knows the current load of each machine. Also, I would like to to assign some kind of machine learning here, because I will know statistics of each job (started, finished, cpu load etc.). How can I distribute jobs (calculations) in the best possible way, keeping in mind the priorities? Any suggestions, ideas, or algorithms ? FYI: My platform .NET.

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  • Are there any well-known algorithms or computer models that computer scientists use to predict FIFA

    - by Khnle
    Occasionally I read news articles that mention about some computer models that computer scientists use to predict winners of some sporting events or the odds for betting which I think there must be a mathematical model behind it. I never bothered to think twice even though I am a "pseudo computer scientist" myself. With the 2010 FIFA World Cup just underway, and since I am also a "pseudo football/soccer player" myself, I just started to wonder about these calculations algorithms. For example, I know one factor is determining the strength of opponents, so that a win against a strong opponent can count more than a win against a weak opponent. But it now kind of gets in a circular loop, or at least how does one determine the strength of a team in the first place, before that team can be considered strong or weak? If it's based on a historical data then there's no way that could be accurate, because those players of the past are no longer on the fields so their impact is none (except maybe if they become coaches like Maradona) Anyway, long question short, if you're happen to be working in this field or have some knowledge, please shed some lights.

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  • Do encryption algorithms provide really unique results?

    - by Mikulas Dite
    I was wondering whether md5, sha1 and anothers return unique values. For example, sha1() for test returns a94a8fe5ccb19ba61c4c0873d391e987982fbbd3, which is 40 characters long. So, sha1 for strings larger than 40 chars must be the same (of course it's scrambled, because the given input may contain whitespaces and special chars etc.). Due to this, when we are storing users' passwords, they can enter either their original password or some super-long one, which nobody knows. Is this right, or do these hash algorithms provide really unique results - I'm quite sure it's hardly possible.

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  • Facebook Graph API: Upload Photo To Album

    - by st4ck0v3rfl0w
    Hello All, I'm trying to familiarize myself with Facebook's new Graph API and so far I can fetch and write some data pretty easily. Something I'm struggling to find decent documentation on is uploading images to an album. According to http://developers.facebook.com/docs/api#publishing you need to supply the message argument. But I'm not quite sure how to construct it. Older resources I've read are: http://wiki.auzigog.com/Facebook_Photo_Uploads http://wiki.developers.facebook.com/index.php/Photos.upload If someone has more information or could help me tackle uploading photos to an album using Facebook Graph API please reply!

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  • Facebook Graph API - authorization types?

    - by Alex Cook
    I'm struggling with the new Facebook Graph API, perhaps someone here can help. Here is what I want to do: provide a ‘login w/ FB’ button, throw to /authorize, get a code, throw to /access_token, get an access_token, and be able to hit https://graph.facebook.com/me for info about the user. When I try to use type=client_cred in the /authorize call, I get an access_token that lets me hit URLs with userIDs or names, but not /me. I receive an error stating I need a valid token. If I can't hit /me, how do I figure out who the current user is? What exactly should I use in the type param if I want a website to access a users data? I've seen posts with type=web_server, etc, but I can't seem to find a sure fire way to do, what I think, is pretty simple... Thanks ahead of time for any help thats provided...

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  • Graphical sandbox for pathfinding

    - by vrode
    If you needed a clean and consistent sandbox for pathfinding what would you use? I want to experiment with different pathfinding algorithms by sending virtual units (robots) around obstacles on a geometric plane. But I don't need a feature overkill like a game engine or Flash might have, just an animated report and native collision detector. I prefer it to be scripted in python, but if there are java or C++ alternatives I would appreciate them as well.

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  • 2d graph in real-time by using opencv and c++

    - by user2758510
    I have a really basic question in opencv and c++. I am trying to graph something in real time by using opencv. I am looking to find a function to draw a graph in rel-time. But still unssuccesful. I need a function that gets two arrays as an input one for x axis and one for y. I tried with this but seems not work in real-time http://www.shervinemami.info/graphs.html I just need to know if there is something available in opencv or not. Thanks in advance.

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  • OBJ-C: Call an instance of core-plot graph from separate view controller

    - by Kevin
    I'm using a view controller i.e. ViewController:UIViewController and have another class GraphViewController:UIViewController . How do I call an instance of GraphViewController and place it into my ViewController? I am currently trying to call the plot within my ViewController directly, but I want to make the graph modular so I don't have to copy code if I use the same graph again. ViewController has methods -(void) refreshGraph; //Inhereted Methods -(NSUInteger)numberOfRecordsForPlot:(CPPlot *)plot; -(NSNumber *)numberForPlot:(CPPlot *)plot field:(NSUInteger)fieldEnum recordIndex:(NSUInteger)index; How do I move these methods to a separate class and then call it to get the same plot in my ViewController? I am sure there must be a thread on this somewhere but I can't seem to find it.

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  • Finding All Ways in FlowChart diagram ?

    - by Meko
    Hi All... I made an FlowChart diagram editor on Java. It It drows flowscharts and connect them each other and creates me two array. One of it shows connection nodes and lines , other shows connnecting elements eachother. I have to find all ways from starting Begin Two And . For example if I have some diamond for decision I have two seperate way ..I want to get all this ways..Which algorithms I must use?

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  • Simple example of popup authentication with Facebook Graph API

    - by ensnare
    Trying to get Facebook to authenticate my users via a javascript popup. Right now, I have: <input type="button" value="Connect with Facebook" onclick="window.open('https://graph.facebook.com/oauth/authorize?client_id=XXXXXXXXXXX&redirect_uri=http://example.com/step2&display=popup')" /> But when the user logs in via Facebook, the popup just displays the Facebook.com homepage. I'd like for the popup to authenticate the user and go away so that I can start retrieving user data from the graph api. Is there a better / easier way to do this? Simple examples are appreciated. Thank you.

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  • Finding a prime number after a given number

    - by avd
    How can I find the least prime number greater than a given number? For example, given 4, I need 5; given 7, I need 11. I would like to know some ideas on best algorithms to do this. One method that I thought of was generate primes numbers through the Sieve of Eratosthenes, and then find the prime after the given number.

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  • Open Graph & Rails not retrieving object's URL

    - by Fred
    I'm using Rails to try and add an action for an object both defined for my app on the open graph. I am using an :after_filter in my controller to call the following after session#create: @graph.put_connections('me', 'workkout:complete', :session => url_for([@plan, @session])) I am getting the following back from Facebook: {"error":{"type":"Exception","message":"Could not retrieve data from URL.","code":1660002}} I have checked that the correct URL is passed to put_connections, and when I visit this URL using Facebook's Lint tool, everything is correct. I can't understand why this isn't working, my only thought is that Facebook is hitting the URL moments before rails has generated the object? - not sure if that's even possible though. Can anyone shed any light on this?

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  • Getting RPXNow and Facebook Open Graph to Play Nicely

    - by ramon.tayag
    A requirement to use the RPXNow is to set your Facebook application's connect url to http://mydomain.rpxnow.com. I was just trying to implement Facebook's Open Graph and I see that it tells you to set the Base Domain to the domain that will contain the app_id. However, Facebook does not allow these two domains to look different. When I try to set the base url to mydomain.com, I get this error: Validation failed. Base Domain is not valid. Connect URL must be derived from your Base Domain. Should I create two apps - one for use with RPXNow, and another for use with Open Graph? If not, what should I do? Thanks

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  • Resources for how to design graph/charts well

    - by wesgarrison
    One of my projects needs to show users where they rank in certain calculations. I inherited the graph structure from the previous programmer and had to leave it alone while I worked on other parts of the site. It's time to make the graphs more meaningful, so I'm looking for books/websites/etc about graphs. (Not graph theory!) Charts that convey comparisons at a glance. Everyone suggests The Visual Display of Quantitative Information by Edward Tufte and that's spot on for what I'm looking for, so anything related to that would be great. Naturally, personal experience about what to do or not would be helpful as well.

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  • MS Access MSChart.Graph.8 not printing

    - by Tanj
    Software: Microsoft Access 2007 SP2 Database File Version: Access 2000 I have an access program that I inherited from a previous employee. It uses forms for reports and since I don't have much experience in access I have continued to do this. I have created a copy of the program for another project and modified it to suit. I am having trouble getting more then one chart to print. All the charts display in form view, they all have the same properties (excepting data, position, etc.) For some reason they are not printing. They don't even show up in the print preview. I am thinking it must be something with the graphs themselves as they sometimes lose all information. I have to open the graphs in edit mode and change the data source from column to row and back again so that it gets redrawn. (Refresh doesn't fix it) So right now I don't even have a clue as to where to look so ideas are welcome. Edit #1 It seems to be a problem with linking to an unbound form. Subform Field Linker: Can't build a link between unbound forms. The query for the main form is SELECT tTest.ixTest, tMotorTypes.ixMotorType, tMotorTypes.asMotorType, tMotorTypes.fDeprecated, tTestType.asTest, tTest.asSerialNum, tTest.asOrderNum, tTest.asFrameNum, tTest.asRotorNum, tTest.asOperator, tTest.iStation, tTest.dtTestDate, tTest.ixTestType FROM tMotorTypes INNER JOIN (tTestType INNER JOIN tTest ON tTestType.ixTestType=tTest.ixTestType) ON tMotorTypes.ixMotorType=tTest.ixMotorType; The query for the chart is: SELECT qGraphRSTTemperatures.Frequency, qGraphRSTTemperatures.[Drive End], qGraphRSTTemperatures.[Non Drive End], qGraphRSTTemperatures.[Air In], qGraphRSTTemperatures.Core FROM qGraphRSTTemperatures ORDER BY qGraphRSTTemperatures.ixTemperature; Query qGraphRSTTemperatures: SELECT tElectricalData.dblFrequency AS Frequency, tTemperatures.dblDrvEnd AS [Drive End], tTemperatures.dblNonDrvEnd AS [Non Drive End], tTemperatures.dblAirIn AS [Air In], tTemperatures.dblCore AS Core, tSubTest.ixTest, tTemperatures.ixTemperature FROM (tSubTest INNER JOIN tElectricalData ON tSubTest.ixSubTest = tElectricalData.ixSubTest) LEFT JOIN tTemperatures ON tElectricalData.ixElectrical = tTemperatures.ixElectrical WHERE (((tSubTest.ixSubTestType)=5)) ORDER BY tSubTest.ixTest, tTemperatures.ixTemperature; So how come, in the form view it shows the graph with the correct data when linked thus: Child field: ixTest Master field: ixTest but won't print the graph. The graph will print if I remove the links, but then I have all the data from chart query as it is not limited by ixTest. edit #2 It seems to be a data retrieval/rendering issue in printing. Is there anything in printing that changes the context of records with respect to parent/child relationships?

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  • Pruning data for better viewing on loglog graph - Matlab

    - by Geodesic
    Hi Guys, just wondering if anyone has any ideas about an issue I'm having. I have a fair amount of data that needs to be displayed on one graph. Two theoretical lines that are bold and solid are displayed on top, then 10 experimental data sets that converge to these lines are graphed, each using a different identifier (eg the + or o or a square etc). These graphs are on a log scale that goes up to 1e6. The first few decades of the graph (< 1e3) look fine, but as all the datasets converge ( 1e3) it's really difficult to see what data is what. There's over 1000 data points points per decade which I can prune linearly to an extent, but if I do this too much the lower end of the graph will suffer in resolution. What I'd like to do is prune logarithmically, strongest at the high end, working back to 0. My question is: how can I get a logarithmically scaled index vector rather than a linear one? My initial assumption was that as my data is lenear I could just use a linear index to prune, which lead to something like this (but for all decades): //%grab indicies per decade ind12 = find(y >= 1e1 & y <= 1e2); indlow = find(y < 1e2); indhigh = find(y > 1e4); ind23 = find(y >+ 1e2 & y <= 1e3); ind34 = find(y >+ 1e3 & y <= 1e4); //%We want ind12 indexes in this decade, find spacing tot23 = round(length(ind23)/length(ind12)); tot34 = round(length(ind34)/length(ind12)); //%grab ones to keep ind23keep = ind23(1):tot23:ind23(end); ind34keep = ind34(1):tot34:ind34(end); indnew = [indlow' ind23keep ind34keep indhigh']; loglog(x(indnew), y(indnew)); But this causes the prune to behave in a jumpy fashion obviously. Each decade has the number of points that I'd like, but as it's a linear distribution, the points tend to be clumped at the high end of the decade on the log scale. Any ideas on how I can do this?

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