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• Longest substring that appears n times

  - by xcoders

  For a string of length L, I want to find the longest substring that appears n (n<L) or more times in ths string. For example, the longest substring that occurs 2 or more times in "BANANA" is "ANA", once starting from index 1, and once again starting from index 3. The substrings are allowed to overlap. In the string "FFFFFF", the longest string that appears 3 or more times is "FFFF". The brute force algorithm for n=2 would be selecting all pairs of indexes in the string, then running along until the characters are different. The running-along part takes O(L) and the number of pairs is O(L^2) (duplicates are not allowed but I'm ignoring that) so the complexity of this algorithm for n=2 would be O(L^3). For greater values of n, this grows exponentially. Is there a more efficient algorithm for this problem?

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• Return specific HREF attribute using Xpath query

  - by Michael Pasqualone

  Having a major brain freeze, I have the following chunk of code: // Get web address $domQuery = query_HtmlDocument($html, '//a[@class="productLink"]'); foreach($domQuery as $rtn) { $web = $rtn->getAttribute('href'); } Which obviously gets the entire href attribute, however I only want 1 specific attribute within the href. I.e. If the href is: /website/product1234.do?code=1234&version=1.3&somethingelse=blaah I only want to return the variable for "version", so wish to only return "1.3" in my example. What's most efficient way to do this?

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• C++ Thread Safe Integer

  - by Paul Ridgway

  Hello everyone, I have currently created a C++ class for a thread safe integer which simply stores an integer privately and has public get a set functions which use a boost::mutex to ensure that only one change at a time can be applied to the integer. Is this the most efficient way to do it, I have been informed that mutexes are quite resource intensive? The class is used a lot, very rapidly so it could well be a bottleneck... Googleing C++ Thread Safe Integer returns unclear views and oppinions on the thread safety of integer operations on different architectures. Some say that a 32bit int on a 32bit arch is safe, but 64 on 32 isn't due to 'alignment' Others say it is compiler/OS specific (which I don't doubt). I am using Ubuntu 9.10 on 32 bit machines, some have dual cores and so threads may be executed simultaneously on different cores in some cases and I am using GCC 4.4's g++ compiler. Thanks in advance...

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• Opinions regarding C++ programming practice

  - by Sagar

  I have a program that I am writing, not too big. Apart from the main function, it has about 15 other functions that called for various tasks at various times. The code works just fine all in one file, and as it is right now. However, I was wondering if anyone had any advice on whether it is smarter/more efficient/better programming to put those functions in a separate file different from where main is, or whether it even matters at all. If yes, why? If no, why not? I am not new at C++, but definitely not an expert either, so if you think this question is stupid, feel free to tell me so. Thanks for your time!

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• to get columns from Excel files using Apache POI??

  - by posdef

  Hi, In order to do some statistical analysis I need to extract values in a column of an Excel sheet. I have been using the Apache POI package to read from Excel files, and it works fine when one needs to iterate over rows. However I couldn't find anything about getting columns neither in the API (link text) nor through google searching. As I need to get max and min values of different columns and generate random numbers using these values, so without picking up individual columns, the only other option is to iterate over rows and columns to get the values and compare one by one, which doesn't sound all that time-efficient. Any ideas on how to tackle this problem? Thanks,

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• Python: Unpack arbitary length bits for database storage

  - by sberry2A

  I have a binary data format consisting of 18,000+ packed int64s, ints, shorts, bytes and chars. The data is packed to minimize it's size, so they don't always use byte sized chunks. For example, a number whose min and max value are 31, 32 respectively might be stored with a single bit where the actual value is bitvalue + min, so 0 is 31 and 1 is 32. I am looking for the most efficient way to unpack all of these for subsequent processing and database storage. Right now I am able to read any value by using either struct.unpack, or BitBuffer. I use struct.unpack for any data that starts on a bit where (bit-offset % 8 == 0 and data-length % 8 == 0) and I use BitBuffer for anything else. I know the offset and size of every packed piece of data, so what is going to be the fasted way to completely unpack them? Many thanks.

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• Best way to collect and store data daily?

  - by mktb

  I have a bunch of statistics: # of users, # of families, ratio user/family, etc. I'd like to store these daily so I can view this data historically. However, I'm looking for the most effective way to store this data. Should I run a cron job that writes to the database DATE: today USERS: 123 FAMILIES: 456 RATIO: 7.89 or whatever? (or should I write multiple rows like DATE: today DATATYPE: users VALUE: 123?) Or is there another option I can use that is more efficient or more effective? Thanks!

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• LINQ to Entity, joining on NOT IN tables

  - by SlackerCoder

  My brain seems to be mush right now! I am using LINQ to Entity, and I need to get some data from one table that does NOT exist in another table. For example: I need the groupID, groupname and groupnumber from TABLE A where they do not exist in TABLE B. The groupID will exist in TABLE B, along with other relevant information. The tables do not have any relationship. In SQL it would be quite simply (there is a more elegant and efficient solution, but I want to paint a picture of what I need) SELECT GroupID, GroupName, GroupNumber, FROM TableA WHERE GroupID NOT IN (SELECT GroupID FROM TableB) Is there an easy/elegant way to do this? Right now I have a bunch of queries hitting the db, then comparing, etc. It's pretty messy. Thanks.

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• Get value from ajax-loaded form before submitting

  - by ldvldv

  Hi, I have an app that loads an ajax form when a button is clicked. I then want to check a value in that ajax loaded form called "comment_content" so that I don't send an ajax request if the comment_content is empty. I can capture the form submission using the live method, however, I can't capture the form element because it needs an element. I was looking at livequery but was wondering if there is a more efficient way by using live or if that I shouldn't even bother? Your help is very much appreciated. $("#comment_submit").live('click', function(){ var comment = $("#comment_content").html(); if(comment == ""){ $("#notice").html("").stop(true, true); $("#notice").append("<p>Are you going to write something in that comment?</p>"); $('#notice').slideDown().delay(2000).slideUp(); return false; } return true; });

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• How to store the result of a JSP in a string?

  - by Spines

  I want to store the result of a JSP in a string. For example, I want to be able to call a function like: String result = ProcessJsp("/jspfile.jsp"); Also, this must be rather efficient. Making a url request to the jsp and then storing it would definitely be too slow. How could I do this? Here are my thoughts on how to do this, though I'm not sure if it would work, and I'm hoping there is something simpler: Do RequestDispatcher("/jspfile.jsp").include(hreq, hresp), but instead of putting the real HttpResponse object in there, you put your own where the getWriter() method returns something that writes to your String or a memory buffer, etc.

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• WPF: How to efficiently update an Image 30 times per second

  - by John

  Hello, I'm writing a WPF application that uses a component, and this component returns a pointer (IntPtr) to pixels of a bitmap (stride * height). I know in advance that the bitmap is a 24bits rgb, its width and height. Updating the Image control with these bitmaps makes up a video to the user, but I'm not sure what's the most efficient way to do that, most of the time the CPU usage goes to 75%+ and memory changing from 40mb to 500mb and the nI think GC starts to work and then it drops again to 40mm. The app starts to not be responsive. What shoud I do? thanks!

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• Programming language for fast calculations with big integers

  - by sub

  I'm doing Project Euler problems at the moment and I can solve most of them using my own programming language which uses direct C++ integers (so they are bound to 2^32 on my machine). However, at times there are problems which require me to work with very high numbers, I can't do that with native integers. So I implemented a BigInt library in my language which unfortunately gets extremely slow at times. Is there a programming language suitable for very efficient handling of big numbers? I mean that I want to do the things I could do in other programming languages with it (variables, loops, etc.), but in a faster way. If you have got tips for workarounds of the 2^32 limit in my language/C++/other languages, please tell me too!

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• C# 4.0: Can I use a Color as an optional parameter with a default value?

  - by DTown

  public void log(String msg, Color c = Color.black) { loggerText.ForeColor = c; loggerText.AppendText("\n" + msg); } This results in an error that c must be a compile-time constant. I've read up on this a little and most examples are dealing with strings and ints. I've figured out I can use the colorconverter class but I'm not sure it will be very efficient. Is there a way to just pass a basic color as an optional parameter? public void log(String msg, String c = "Black") { ColorConverter conv = new ColorConverter(); Color color = (Color)conv.ConvertFromString(c); loggerText.ForeColor = color; loggerText.AppendText("\n" + msg); }

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• How do I request a single random row from a force.com database in SOQL?

  - by Ollie C

  Total row-count is in the range 10k-100k rows. Can I use RAND() on force.com? Unfortunately although all the rows have a unique numeric identifier, there are many gaps, and I'd often want to select a random row from a filtered subset anyway. I suspect there's no particularly efficient way to do this, but is it possible at all? Ultimately all I want to do is to extract one row from a table (or a subset based on specific filter criteria) at random. If force.com doesn't let me select a random row, then can I query the rows to select from, and assign sequential IDs to all the rows, say 1-1,035, and then select a random number in that range locally, say 349, and then get row 349?

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• When calling CRUD check if "parent" exists with read or join?

  - by Trick

  All my entities can not be deleted - only deactivated, so they don't appear in any read methods (SELECT ... WHERE active=TRUE). Now I have some 1:M tables on this entities on which all CRUD operations can be executed. What is more efficient or has better performance? My first solution: To add to all CRUD operations: UPDATE ... JOIN entity e ... WHERE e.active=TRUE My second solution: Before all CRUD operations check if entity is active: if (getEntity(someId) != null) { //do some CRUD } In getEntity there's just SELECT * FROM entity WHERE id=? AND active=TRUE. Or any other solution, recommendation,...?

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• Is there an optimal way to render images in cocoa? Im using setNeedsDisplay

  - by Edward An

  Currently, any time I manually move a UIImage (via handling the touchesMoved event) the last thing I call in that event is [self setNeedsDisplay], which effectively redraws the entire view. My images are also being animated, so every time a frame of animation changes, i have to call setNeedsDisplay. I find this to be horrific since I don't expect iphone/cocoa to be able to perform such frequent screen redraws very quickly. Is there an optimal, more efficient way that I could be doing this? Perhaps somehow telling cocoa to update only a particular region of the screen (the rect region of the image)?

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• Refresh a ListView if I change the content of the ListItem

  - by michael

  Hi, I have a ListView in my android activity. And I populate the ListView by sub-class the BaseAdaptor (which returns a View in getView() method). What if in my click listener of a button in a list item view, I change the text of the TextView in the List item view or change the dimension of the list item view by adding/removing children of the list item view What is an efficient to refresh my listView? I don't want the listView to re-trigger a query since there is no data change. Thank you.

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• What's the fastest way to scrape a lot of pages in php?

  - by Yegor

  I have a data aggregator that relies on scraping several sites, and indexing their information in a way that is searchable to the user. I need to be able to scrape a vast number of pages, daily, and I have ran into problems using simple curl requests, that are fairly slow when executed in rapid sequence for a long time (the scraper runs 24/7 basically). Running a multi curl request in a simple while loop is fairly slow. I speeded it up by doing individual curl requests in a background process, which works faster, but sooner or later the slower requests start piling up, which ends up crashing the server. Are there more efficient ways of scraping data? perhaps command line curl?

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• Fastest way to check a List<T> for a date

  - by fishhead

  I have a list of dates that a machine has worked on, but it doesn't include a date that machine was down. I need to create a list of days worked and not worked. I am not sure of the best way to do this. I have started by incrementing through all the days of a range and checking to see if the date is in the list by iterating through the entire list each time. I am looking for a more efficient means of finding the dates. class machineday { datetime WorkingDay; } class machinedaycollection : List<machineday> { }

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• Problem re-factoring multiple timer countdown

  - by Joko Wandiro

  I create my multiple timer countdown from easy or simple script. entire code The problem's happen when i want to add timer countdown again i have to declare variable current_total_second CODE: elapsed_seconds= tampilkan("#time1"); and variable timer who set with setInterval.. timer= setInterval(function() { if (elapsed_seconds != 0){ elapsed_seconds = elapsed_seconds - 1; $('#time1').text(get_elapsed_time_string(elapsed_seconds)) }else{ $('#time1').parent().slideUp('slow', function(){ $(this).find('.post').text("Post has been deleted"); }) $('#time1').parent().slideDown('slow'); clearInterval(timer); } }, 1000); i've already know about re-factoring and try different way but i'm stack to re-factoring this code i want implement flexibelity to it.. when i add more of timer countdown.. script do it automatically or dynamically without i have to add a bunch of code.. and the code become clear and more efficient. Thanks in Advance

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• C#/WPF FileSystemWatcher on every extension on every path

  - by BlueMan

  I need FileSystemWatcher, that can observing same specific paths, and specific extensions. But the paths could by dozens, hundreds or maybe thousand (hope not :P), the same with extensions. The paths and ext are added by user. Creating hundreds of FileSystemWatcher it's not good idea, isn't it? So - how to do it? Is it possible to watch/observing every device (HDDs, SD flash, pendrives, etc.)? Will it be efficient? I don't think so... . Every changing Windows log file, scanning file by antyvirus program - it could realy slow down my program with SystemWatcher :(

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• Choose item from a list with bias?

  - by ooboo

  Given a list of items x1 ... xn and associated probabilties p1 ... pn that sum up to 1 there's a well known procedure to select a random item with its associated proabability by sorting the list according to weight, choosing a random value between 1 and 0, and adding up to a culmination sum until it exceeds the value selected and return the item at this point. So if we have x1 - 0.5, x2 - 0.3, x3 - 0.2, if the randomly chosen value is less than 0.5 x1 will be chosen, if between 0.5 and 0.8, x2, and else x3. This requires sorting so it needs O(nlogn) time. Is there anything more efficient than that?

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• Base64 Encoded Data - DB or Filesystem

  - by Marty

  I have a new program that will be generating a lot of Base64 encoded audio and image data. This data will be served via HTTP in the form of XML and the Base64 data will be inline. These files will most likely break 20MB and higher. Would it be more efficient to serve these files directly from the filesystem or would it be feasible to store the data in a MySQL database? Caching will be set up but overall unnecessary because it is likely that this data will be purged shortly after it is created and served. i know that storing binary data in the DB is frowned upon in most circumstances but since this will all be character data I want to see what the consensus is. As of now, I am leaning toward storing them in the filesystem for efficiency reasons but if it is feasible to store them in a database it would be much easier to manage the data.

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• Determining whether a file is a duplicate

  - by Todd R

  Is there a reliable way to determine whether or not two files are the same? For example, two files with the same size and type may or may not be the same binarilly (yeah, I know it's not really a word). I assume that comparing one or two checksums of the files will help, but I wonder: How reliable are checksums at determining whether two files are different; what are the chances of two different files having the same checksum? Would reliability increase by applying additional checksum comparisons? Which checksum algorithm(s) would be the most efficient and/or reliable? Any ideas, suggestions or thoughts are appreciated! P.S. The code for this is being written in Java running on a nix system, but generic or platform agnostic input is most helpful.

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• Prims vs Polys: what are the pros and cons of each?

  - by Richard Inglis

  I've noticed that most 3d gaming/rendering environments represent solids as a mesh of (usually triangular) 3d polygons. However some examples, such as Second Life, or PovRay use solids built from a set of 3d primitives (cube, sphere, cone, torus etc) on which various operations can be performed to create more complex shapes. So my question is: why choose one method over the other for representing 3d data? I can see there might be benefits for complex ray-tracing operations to be able to describe a surface as a single mathematical function (like PovRay does), but SL surely isn't attempting anything so ambitious with their rendering engine. Equally, I can imagine it might be more bandwidth-efficient to serve descriptions of generalised solids instead of arbitrary meshes, but is it really worth the downside that SL suffers from (ie modelling stuff is really hard, and usually the results are ugly) - was this just a bad decision made early in SL's development that they're now stuck with? Or is it an artefact of what's easiest to implement in OpenGL?

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