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• Text editing best practices (with tags, etc.)

  - by Ron

  Hi there, I want to create a text field with some text, that is styled with tags. Think of MS Word, some ext is bold, some is a headline, etc. The tags that style the text are not visible to the user, he just sees the text in bold. How do I preserve these tags? I mean when I backspace over the closing bold-tag, for example, how do I preserve that and prevent that the rest of the text is now bold until the end? I guess this is a pretty basic question for experiences programmers. Are there any algorithms or best practices? This problem surely has been solved before, any pointers? (If this is of any concern, I develop for the iPhone OS and the text field will be a UITextView, but my question is more general I guess.) Thanks in advance!

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• FIPS-compliant encryption in .NET 2.0

  - by Odrade

  We have a .NET 2.0 application that uses the RijindaelManaged class to encrypt some sensitive data. This was fine until we ran into some machines that require the use of FIPS-compliant algorithms. We'd like to switch to AesCryptoServiceProvider, but most of our target machines haven't upgraded past .NET 2.0. Requiring an upgrade is out of the question. After all, upgrades are scary! Is there any way we could use AesCryptoServiceProvider in a .NET 2.0 application? Since 3.5 uses the 2.0 CLR, I was hoping there might be a way to build the needed libraries into the app. Failing that, could someone point me to a reference on the native API that's wrapped by AesCryptoServiceProvider?

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• Math: How to sum each row of a matrix

  - by macek

  I have a 1x8 matrix of students where each student is a 4x1 matrix of scores. Something like: SCORES S [62, 91, 74, 14] T [59, 7 , 59, 21] U [44, 9 , 69, 6 ] D [4 , 32, 28, 53] E [78, 99, 53, 83] N [48, 86, 89, 60] T [56, 71, 15, 80] S [47, 67, 79, 40] Main question: Using sigma notation, or some other mathematical function, how can I get a 1x8 matrix where each student's scores are summed? # expected result TOTAL OF SCORES S [241] T [146] U [128] D [117] E [313] N [283] T [222] S [233] Sub question. To get the average, I will multiply the matrix by 1/4. Would there be a quicker way to get the final result? AVERAGE SCORE S [60.25] T [36.50] U [32.00] D [29.25] E [78.25] N [70.75] T [55.50] S [58.25] Note: I'm not looking for programming-related algorithms here. I want to know if it is possible to represent this with pure mathematical functions alone.

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• Boost graph libraries: setting edge weight values

  - by AndyUK

  I am investigating the use of the boost graph libraries in order to apply them to various network problems I have in mind. In the examples I have been looking at the graph edge values ("weights") are always initialized as integers, such as in these Bellman-Ford and Kruskal algorithms eg: int weights[] = { 1, 1, 2, 7, 3, 1, 1, 1 }; My problem is if I try and change the weights to double, I get a heap of warning messages about conversions etc, which so far I have not been able to figure out how to overcome. Does anyone see a way around this?

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• big O notation algorithm

  - by niggersak

  Use big-O notation to classify the traditional grade school algorithms for addition and multiplication. That is, if asked to add two numbers each having N digits, how many individual additions must be performed? If asked to multiply two N-digit numbers, how many individual multiplications are required? . Suppose f is a function that returns the result of reversing the string of symbols given as its input, and g is a function that returns the concatenation of the two strings given as its input. If x is the string hrwa, what is returned by g(f(x),x)? Explain your answer - don't just provide the result!

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• Comparison of music data

  - by Christian P.

  Hey I am looking for theory, algorithms and similar for how to compare music. More specifically, I am looking into how to dupecheck music tracks that have different bitrates or perhaps slightly different variations (radio vs album version), but otherwise sound the same. Use cases for this include services such as Grooveshark, Youtube, etc. where they get a lot of duplicate tracks. I am also interested in text comparisons (Britney Spers vs Britney Spears, how far they deviate, etc.) although this is secondary and I already have some sources to go on in this area. I am mostly interested in codec-agnostic comparison techniques and algoritms (assuming a "raw" stream), but codec-specific resources are appreciated. I am aware of projects such as musicbrainz.org, but have not investigated it further, and would be interested if such projects could be of help in this endeavor.

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• Is it a good idea to create an STL iterator which is noncopyable?

  - by BillyONeal

  Most of the time, STL iterators are CopyConstructable, because several STL algorithms require this to improve performance, such as std::sort. However, I've been working on a pet project to wrap the FindXFile API (previously asked about), but the problem is it's impossible to implement a copyable iterator around this API. A find handle cannot be duplicated by any means -- DuplicateHandle specifically forbids passing handles to it. And if you just maintain a reference count to the find handle, then a single increment by any copy results in an increment of all copies -- clearly that is not what a copy constructed iterator is supposed to do. Since I can't satisfy the traditional copy constructible requirement for iterators here, is it even worth trying to create an "STL style" iterator? On one hand, creating some other enumeration method is going to not fall into normal STL conventions, but on the other, following STL conventions are going to confuse users of this iterator if they try to CopyConstruct it later. Which is the lesser of two evils?

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• C++: building iterator from bits

  - by gruszczy

  I have a bitmap and would like to return an iterator of positions of set bits. Right now I just walk the whole bitmap and if bit is set, then I provide next position. I believe this could be done more effectively: for example build statically array for each combination of bits in single byte and return vector of positions. This can't be done for a whole int, because array would be too big. But maybe there are some better solutions? Do you know any smart algorithms for this?

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• Java Memory Management

  - by Tara Singh

  I am designing a client-server chat application in Java. This is a secure application where the messages are exchanged using cryptographic algorithms. I have one server and it can support many clients. My problem is that when one client logs on the server it works fine, but when another user logs into the system, the server starts giving me bad padding exceptions for the encrypted text. I am not able to figure out the problem, according to my logic, when new connection request to server is made, the server creates a thread for listening to the client. Is it possible that once the instance of thread class is created, it does all the processing correctly for the first client, but not for the second client because the variables in server listener thread class already have some previous value, and thus the encrypted text is not decrypted properly? Please advise how I can make this process more robust so that the number of clients does not affect how well the server functions.

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• In LaTeX prefer figures on text-heavy pages.

  - by bjarkef

  Hi LaTeX seems to have a preference for placing figures together on a page, and placing surrounding text on a separate page. Can I somehow change that balance a bit, as I prefer figures to break up the text to avoid too black text-heavy pages. Example: \section{Some section} [Half a page of text] \begin{figure} [...] \caption{Figure text 1} \end{figure} [Half a page of text] \begin{figure} [...] \caption{Figure text 2} \end{figure} [More text] So what LaTeX usually does is to stack the two half pages of text on a single page, and the figures on the following page. I believe this really gives a bad balance, and bores the reader. So can I change that somehow? I know about postfixing the \begin{figure} with [ht!], but often it does not really matter. I would like to configure the balancing algorithms in LaTeX to naturally prefer pages with combined figures and text.

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• What's the best general programming book to review basic development concepts?

  - by Charles S.

  I'm looking for for a programming book that reviews basic concepts like implementing linked lists, stacks, queues, hash tables, tree traversals, search algorithms, etc. etc. Basically, I'm looking for a review of everything I learned in college but have forgotten. I prefer something written in the last few years that includes at least a decent amount of code in object-oriented languages. This is to study for job interview questions but I already have the "solving interview questions" books. I'm looking for something with a little more depth and explanation. Any good recommendations?

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• Efficient heaps in purely functional languages

  - by Kim

  As an exercise in Haskell, I'm trying to implement heapsort. The heap is usually implemented as an array in imperative languages, but this would be hugely inefficient in purely functional languages. So I've looked at binary heaps, but everything I found so far describes them from an imperative viewpoint and the algorithms presented are hard to translate to a functional setting. How to efficiently implement a heap in a purely functional language such as Haskell? Edit: By efficient I mean it should still be in O(n*log n), but it doesn't have to beat a C program. Also, I'd like to use purely functional programming. What else would be the point of doing it in Haskell?

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• How to do a natural sort on an NSArray?

  - by Cory Imdieke

  I've got an array of objects, and I need them sorted by their "title" key. It's currently working, though it's using an ASCII sort instead of a natural sort. The titles are filenames, so they look like this: file1 file2 file3 ... file10 file11 file12 I'm getting, as you would expect: file1 file10 file11 file12 file2 file3 ... Does anyone know if there is a way built-in to the NSArray sorting functionality to get this natural sorting as opposed to the alphabetical sort? I found some generic algorithms, but I was hoping for something built-in...

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• graphviz segmentation fault

  - by LucaB

  Hi I'm building a graph with many nodes, around 3000. I wrote a simple python program to do the trick with graphviz, but it gives me segmentation fault and I don't know why, if the graph is too big or if i'm missing something. The code is: #!/usr/bin/env python # Import graphviz import sys sys.path.append('..') sys.path.append('/usr/lib/graphviz') import gv # Import pygraph from pygraph.classes.graph import graph from pygraph.classes.digraph import digraph from pygraph.algorithms.searching import breadth_first_search from pygraph.readwrite.dot import write # Graph creation gr = graph() file = open('nodes.dat', 'r') line = file.readline() while line: gr.add_nodes([line[0:-1]]) line = file.readline() file.close() print 'nodes finished, beginning edges' edges = open('edges_ok.dat', 'r') edge = edges.readline() while edge: gr.add_edge((edge.split()[0], edge.split()[1])) edge = edges.readline() edges.close() print 'edges finished' print 'Drawing' # Draw as PNG dot = write(gr) gvv = gv.readstring(dot) gv.layout(gvv,'dot') gv.render(gvv,'svg','graph.svg') and it crashes at the gv.layout() call. The files are somthing like: nodes: node1 node2 node3 edges_ok: node1 node2 node2 node3

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• Interpreting Search Results

  - by Simon

  Hi all, I am tasked with writing a program that, given a search term and the HTML source of a page representing search results of some unknown search engine (it can really be anything, a blog, a shop, Google, eBay, ...), needs to build a data structure of the results containing "what's in the results": a title for earch result, the "details" link, the position within the results etc. It is not known whether the results page contains any of the data at all, and whether there are any search results. The goal is to feed the data structure into another program that extracts meaning. What I am looking for is not BeautifulSoup or a RegExp but rather some clever ideas or algorithms on how to interpret the HTML source. What do I do to find out what part of the page constitutes a single result item? How do I filter the markup noise to extract the important bits? What would you do? Pointers to fields of research covering what I try to to are aly greatly appreciated. Thanks, Simon

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• Tough question on WPF, Win32, MFC

  - by Mack

  Let's suppose you're an IT student with a basic knowledge of C++ and C#. Let's suppose that you want to design apps that: need to deliver some performance like archivers, cryptographic algorithms, codecs make use of some system calls have a gui and you want to learn an Api that will enable you to write apps like those described earlier and: is mainstream is future proof entitles you to find a decent job is easy enough - I mean easy like VCL, not easy like winapi So, making these assumptions, what Api will you choose? MFC, WPF, other? I really like VCL and QT, but they're not mainstream and I think few employers will want you to write apps in QT or Visual C++ Builder... Thanks for answers.

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• Minimizing the number of boxes that cover a given set of intervals

  - by fortran

  Hi, this is a question for the algorithms gurus out there :-) Let S be a set of intervals of the natural numbers that might overlap and b a box size. Assume that for each interval, the range is strictly less than b. I want to find the minimum set of intervals of size b (let's call it M) so all the intervals in S are contained in the intervals of M. Trivial example: S = {[1..4], [2..7], [3..5], [8..15], [9..13]} b = 10 M = {[1..10], [8..18]} // so ([1..4], [2..7], [3..5]) are inside [1..10] and ([8..15], [9..13]) are inside [8..18] I think a greedy algorithm might not work always, so if anybody knows of a solution of this problem (or a similar one that can be converted into), that would be great. Thanks!

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• How do you protect code from leaking outside?

  - by cubex

  Besides open-sourcing your project and legislation, are there ways to prevent, or at least minimize the damages of code leaking outside your company/group? We obviously can't block Internet access (to prevent emailing the code) because programmer's need their references. We also can't block peripheral devices (USB, Firewire, etc.) The code matters most when it has some proprietary algorithms and in-house developed knowledge (as opposed to regular routine code to draw GUIs, connect to databases, etc.), but some applications (like accounting software and CRMs) are just that: complex collections of routine code that are simple to develop in principle, but will take years to write from scratch. This is where leaked code will come in handy to competitors. As far as I see it, preventing leakage relies almost entirely on human process. What do you think? What precautions and measures are you taking? And has code leakage affected you before?

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• What's the difference between the 'DES' class and The 'DESCryptoServiceProvider' class?

  - by IbrarMumtaz

  All I can make out is that one of them is the BC for all 'DES' algorithms to be derived from and the later is a wrapper for the Cryptographic service provider implementation of the DES algorithm. The reason why I ask is that I am going over .Net Security and the MS official training book simply refers to the DES class but the another official MS book refers to the DESCrypto' class. What's the difference between these two? When would you use either of them? What do I need to know as far as the 70-536 exam is concerned. I am asking my question from an educational P.O.V as far as the 70-536 exam is concerned. Thanks In Advance. Ibrar

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• Drawing Directed Acyclic Graphs: Minimizing edge crossing?

  - by Robert Fraser

  Laying out the verticies in a DAG in a tree form (i.e. verticies with no in-edges on top, verticies dependent only on those on the next level, etc.) is rather simple without graph drawing algorithms such as Efficient Sugimiya. However, is there a simple algorithm to do this that minimizes edge crossing? (For some graphs, it may be impossible to completely eliminate edge crossing.) A picture says a thousand words, so is there an algorithm that would suggest: instead of: EDIT: As the picture suggests, a vertex's inputs are always on top and outputs are always below, which is another barrier to just pasting in an existing layout algorithm.

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• How can I learn the math necessary for working with computer vision?

  - by Duncan Benoit

  I know that computer vision involves a lot of math, but I need some tips about how programmers gain that knowledge. I've started to use the OpenCV library but I have some major problems in understanding how the math works in the algorithms. In college I have studied some math and we worked with matrices and derivatives, but I didn't pay to much attention to the subject. It seemed to be so difficult and useless from a programmer point of view. I suppose that there has to be some easy way to understand what a second derivative is without calculating an equation. (Derivatives are just an example) Do you have any tips for me about how can i gain such knowledge? A forum, book, link, advice, anything?

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• Depth First Search Basics

  - by cam

  I'm trying to improve my current algorithm for the 8 Queens problem, and this is the first time I'm really dealing with algorithm design/algorithms. I want to implement a depth-first search combined with a permutation of the different Y values described here: http://en.wikipedia.org/wiki/Eight_queens_puzzle#The_eight_queens_puzzle_as_an_exercise_in_algorithm_design I've implemented the permutation part to solve the problem, but I'm having a little trouble wrapping my mind around the depth-first search. It is described as a way of traversing a tree/graph, but does it generate the tree graph? It seems the only way that this method would be more efficient only if the depth-first search generates the tree structure to be traversed, by implementing some logic to only generate certain parts of the tree. So essentially, I would have to create an algorithm that generated a pruned tree of lexigraphic permutations. I know how to implement the pruning logic, but I'm just not sure how to tie it in with the permutation generator since I've been using next_permutation. Is there any resources that could help me with the basics of depth first searches or creating lexigraphic permutations in tree form?

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• Moderating computer-addiction through programming

  - by every_answer_gets_a_point

  i have an addiction to be on the computer all the time. it doesn't matter what i am doing as long as i am in front of it. i feel like the whole world is here and this is all that matters. i found that through some intellectual stimulation, like writing algorithms, it has helped me to be more satisfied with the time on the computer and i dont need it as much. if any of you have had experience with reliving your computer anxiety through writing code, can you tell me exactly what you wrote, and what you may recommend i work on? thank you for your programming advice

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• Specification, modeling and programming are principially the same, right?

  - by Gabriel Šcerbák

  In formal specifications based on abstract algebraic types and equational theory you use formulas of equational theory to specify theory. System which will satisfy those constraints is called in formal logic a model. Modeling is process of creating a model, which abstracts of some aspects, which are unnecessary details for a specific case. So concrete system has to adhere to created model in observed aspects. Programming is a process of creating a program which will have specific behaviour - will perform specific algorithms - and programming languages through different paradigms enable us to think in a certain specific way, which abstracts of some details, usually machine specific ones. So could we be doing all those things at the same time, because they are principially the same? Is declarative programming the nearest attempt to do that? Could we use some sort f programming languages which will be good for programming as well as for modeling and specification?

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• Any implementations of graph st-ordering or ear-decomposition?

  - by chang

  I'm in the search for an implementation of an ear-decomposition algorithm (http://www.ics.uci.edu/~eppstein/junkyard/euler/ear.html). I examined networkx and didn't find one. Although the algorithm layout is vaguely in my mind, I'd like to see some reference implementation, too. I'm aware of Ulrik Brandes publication on a linear time Eager st-ordering algorithm, which results in an ear decomposition as a side product, if I understand correctly (it even includes pseudocode, which I'm trying to base my implementation on). Side problem: First step could be an st-ordering of a graph. Are there any implementations for st-ordering algorithms you know? Thanks for your input. I'd really like to contribute e.g. to networkx by implementing the ear-decomposition algorithm in python.

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