Search Results

Search found 1848 results on 74 pages for 'algorithms'.

Page 55/74 | < Previous Page | 51 52 53 54 55 56 57 58 59 60 61 62  | Next Page >

• 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?

  Read the article

• 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?

  Read the article

• 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?

  Read the article

• 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

  Read the article

• 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...

  Read the article

• 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

  Read the article

• 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!

  Read the article

• 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.

  Read the article

• 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?

  Read the article

• 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.

  Read the article

• 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

  Read the article

• 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?

  Read the article

• 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?

  Read the article

• 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

  Read the article

• 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.

  Read the article

• I like to learn computer science and programming, but i have no understanding.

  - by Josiah

  Hi all, I like to learn computer science and programming, but i don't know where and how to start. For the past two months, i have been researching on types of programming, i found my interest in desktop programming, and also found this subjects (discrete maths, logic, algorithms, data structures, artificial intelligence, simulation) said to be a most known (subjects). Well as a beginner, i have no understanding on what type of language or books that can cover all these subjects, or even how to write any code. Secondly, am as young as you can guess and i need a language to start with that will be easy for me to understand, and books to read. Thank you.

  Read the article

• 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?

  Read the article

• Performance optimization strategies of last resort?

  - by jerryjvl

  There are plenty of performance questions on this site already, but it occurs to me that almost all are very problem-specific and fairly narrow. And almost all repeat the advice to avoid premature optimization. Let's assume: the code already is working correctly the algorithms chosen are already optimal for the circumstances of the problem the code has been measured, and the offending routines have been isolated all attempts to optimize will also be measured to ensure they do not make matters worse What I am looking for here is strategies and tricks to squeeze out up to the last few percent in a critical algorithm when there is nothing else left to do but whatever it takes. Ideally, try to make answers language agnostic, and indicate any down-sides to the suggested strategies where applicable. I'll add a reply with my own initial suggestions, and look forward to whatever else the SO community can think of.

  Read the article

• Hash Table: Should I increase the element count on collisions?

  - by Nazgulled

  Hi, Right now my hash tables count the number of every element inserted into the hash table. I use this count, with the total hash table size, to calculate the load factor and when it reaches like 70%, I rehash it. I was thinking that maybe I should only count the inserted elements with fills an empty slot instead of all of them. Cause the collision method I'm using is separate chaining. The factor load keeps increasing but if there can be a few collisions leaving lots of empty slots on the hash table. You are probably thinking that if I have that many collisions, maybe I'm not using the best hashing method. But that's not the point, I'm using one of the know hashing algorithms out there, I tested 3 of them on my sample data and selected the one who produced less collisions. My question still remains. Should I keep counting every element inserted, or just the ones that fill an empty slot in the Hash Table?

  Read the article

• Redundancy algorithm for reading noisy bitstream

  - by Tedd Hansen

  I'm reading a lossy bit stream and I need a way to recover as much usable data as possible. There can be 1's in place of 0's and 0's in palce of 1's, but accuracy is probably over 80%. A bonus would be if the algorithm could compensate for missing/too many bits as well. The source I'm reading from is analogue with noise (microphone via FFT), and the read timing could vary depending on computer speed. I remember reading about algorithms used in CD-ROM's doing this in 3? layers, so I'm guessing using several layers is a good option. I don't remember the details though, so if anyone can share some ideas that would be great! :) Edit: Added sample data Best case data: in: 0000010101000010110100101101100111000000100100101101100111000000100100001100000010000101110101001101100111000101110000001001111011001100110000001001100111011110110101011100111011000100110000001000010111 out: 0010101000010110100101101100111000000100100101101100111000000100100001100000010000101110101001101100111000101110000001001111011001100110000001001100111011110110101011100111011000100110000001000010111011 Bade case (timing is off, samples are missing): out: 00101010000101101001011011001110000001001001011011001110000001001000011000000100001011101010011011001 in: 00111101001011111110010010111111011110000010010000111000011101001101111110000110111011110111111111101 Edit2: I am able to controll the data being sent. Currently attempting to implement simple XOR checking (though it won't be enough).

  Read the article

• Are all the system's floating points operations the same?

  - by Jj

  We're making this web app in PHP and when working in the reports we have Excel files to compare our results to make sure our coding is doing the right operations. Now we're running into some differences due floating point arithmetics. We're doing the same divisions and multiplications and running into slightly different numbers, that add up to a notable difference. My question is if Excel is delegating it's floating point arithmetic to the CPU and PHP is also relying in the CPU for it's operations. Or does each application implements its own set of math algorithms?

  Read the article

• what is the idea behind scaling an image using lanczos?

  - by banister

  Hi, I'm interested in image scaling algorithms and have implemented the bilinear and bicubic methods. However, I have heard of the lanczos and other more sophisticated methods for even higher quality image scaling and I am very curious how they work. Could someone here explain the basic idea behind scaling an image using lanczos (both upscaling and downscaling) and why it results in higher quality? I do have a background in fourier analysis and have done some signal processing stuff in the past, but not with relation to image processing, so don't be afraid to use terms like "frequency response" and such in your answer :) EDIT: I guess what i really want to know is the concept and theory behind using a convolution filter for interpolation. (Note: i have already read the wikipedia article on lanczos resampling but it didn't have nearly enough detail for me) thanks alot!

  Read the article

• Which build tool to teach?

  - by Helper Method

  While similiar questions have been asked, this one's focused on which is best/easiest to teach. I'm giving a weekly tutorial at my university focusing on data structures and algorithms. Fromn time to time I introduce tools which may prove helpful in future projects like JUnit, Mercurial, Eclipse etc.. I plan to show them some kind of build tool but I'm not sure which one to choose. I by myself have very little knowledge about build tools, except a little experience in using make. It's more the concept of a build tool I want to show them, not a special tool per se. Which would be the most easiest/future proof/whatever tool to show them? I've read a little bit about Gradle, which looks nice, but so far I think Ant could be a good choice (it's a Java course I'm giving).

  Read the article

• Can I encrypt value in C# and use that with SQL Server 2005 symmetric encryption?

  - by Robert Byrne

  To be more specific, if I create a symmetric key with a specific KEY_SOURCE and ALGORITHM (as described here), is there any way that I can set up the same key and algorithm in C# so that I can encrypt data in code, but have that data decrypted by the symmetric key in Sql Server? From the research I've done so far, it seems that the IDENTITY_VALUE for the key is also baked into the cypher text, making things even more complex. I'm thinking about just trying all the various ways I can think of, ie hashing the KEY_SOURCE using different hash algorithms for a key and trying different ways of encrypting the plain text until I get something that works. Or is that just futile? Has anyone else done this, any pointers? UPDATE Just to clarify, I want to use NHibernate on the client side, but theres a bunch of stored procedures on the database side that still perform decryption.

  Read the article

• C++ defines for a 'better' Release mode build in VS

  - by darid

  I currently use the following preprocessor defines, and various optimization settings: WIN32_LEAN_AND_MEAN VC_EXTRALEAN NOMINMAX _CRT_SECURE_NO_WARNINGS _SCL_SECURE_NO_WARNINGS _SECURE_SCL=0 _HAS_ITERATOR_DEBUGGING=0 My question is what other things do fellow SOers use, add, define, in order to get a Release Mode build from VS C++ (2008,2010) to be as performant as possible? btw, I've tried PGO etc, it does help a bit but nothing that comes to parity, also I'm not using streams, the C++ i'm talking about its more like C but making use of templates and STL algorithms. As it stands now very simple code segments flop when compared to what GCC produces on say an equivalent x86 machine running linux (2.6+ kernel) using 02. Side-Note: I believe a lot of the issues relate directly to the STL version (Dinkum) provided by MS. Could people please elaborate on experiences using STLPort etc with VS C++.

  Read the article

< Previous Page | 51 52 53 54 55 56 57 58 59 60 61 62  | Next Page >