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• Variation on Hamiltonian path problems

  - by Robert

  Thinking about if we modify the definition of Hamiltonian path as we need to go through every edge once,but can pass vertex any times,is there still an algorithm available? How should I modify the original Hamiltonian algorithm to account for this?

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• Find if there is an element repeating itself n/k times

  - by gleb-pendler

  You have an array size n and a constant k (whatever) You can assume the the array is of int type (although it could be of any type) Describe an algorithm that finds if there is an element(s) that repeats itself at least n/k times... if there is return one. Do so in linear time (O(n)) The catch: do this algorithm (or even pseudo-code) using constant memory and running over the array only twice

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• Are there algorithms for increasing resolution of an image?

  - by David

  Are there any algorithms or tools that can increase the resolution of an image - besides just a simple zoom that makes each individual pixel in the image a little larger? I realize that such an algorithm would have to invent pixels that don't really exist in the original image, but I figured there might be some algorithm that could intelligently figure out what pixels to add to the image to increase its resolution.

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• Challenging question find if there is an element repeating himself n/k times

  - by gleb-pendler

  here how it's goes: You have an array size n and a constant k (whatever) you can assume the the array of int type tho it kind be of whatever type but just for the clearane let assume it's an integer. Describe an algorithm that finds if there is an element/s that repeat itself at least n/k times... if there is return one - do it in linear time running O(n) Imortent: now the catch do this algorithm or even pseuo-code using a constant usage of memory and running over the array only TWICE!!!

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• What does ZIP stand for (the compression format, not the postal codes)

  - by codymanix

  Does anybody know for what the acronym ZIP stands for which was and is used in programs like PKZIP and GZIP? There is a compression algorithm named Lempel-Ziv-Welch-Algorithm (LZW) maybe the guy named Ziv invented together with other people ZIP? I cannot find anything about it, maybe its not an abbreviation but instead it just means "to zip files" but I think originally there was more about it..

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• multiplying big numbers using recursion and array

  - by persian Dev

  hi friends. I am supposed to write and algorithm which uses recursion (Divide-And-Conquer) to multiply two arrays.These arrays hold big Numbers that are greater than long(int 64) or double capacity. Would please help to write this algorithm in C#?

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• Linear-time algorithms for sorting vertices in polygon contours

  - by Cheery

  I figured out an algorithm that lets me turn my holed polygons into trapezoids in linear time if I have vertex indices sorted from lowest coordinate to highest. I get simple polygons as contours. They have certain order that might be exploited most of the time. So giving these conditions, is there a near-linear-time algorithm on sorting?

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• Sorting a 2 dimensional array on multiple columns

  - by Anon

  I need to sort a 2 dimensional array of doubles on multiple columns using either C or C++. Could someone point me to the algorithm that I should use or an existing library (perhaps boost?) that has this functionality? I have a feeling that writing a recursive function may be the way to go but I am too lazy to write out the algorithm or implement it myself if it has been done elsewhere. :-) Thanks

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• Drawing Directed Acyclic Graphs: Using DAG property to improve layout/edge routing?

  - by Robert Fraser

  Hi, 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. 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:

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• how to swap array-elements to transfer the array from a column-like into a row-like representation

  - by Christian Ammer

  For example: the array a1, a2, a3, b1, b2, b3, c1, c2, c3, d1, d2, d3 represents following table a1, b1, c1, d1 a2, b2, c2, d2 a3, b3, c3, d3 now i like to bring the array into following form a1, b1, c1, d1, a2, b2, c2, d2, a3, b3, c3, d3 Does an algorithm exist, which takes the array (from the first form) and the dimensions of the table as input arguments and which transfers the array into the second form? I thougt of an algorithm which doesn't need to allocate additional memory, instead i think it should be possible to do the job with element-swap operations.

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• Detect session hang and kill it

  - by Jack Juiceson

  Hi all, I have an asp.net page that runs certain algorithm and returns it's output. I was wondering what will happen and how to handle a case where the algorithm due to a bug goes into infinite loop. It will hog the cpu and other sessions will be served very slowly. I would love to have a way to tell IIS, if processing Algo.aspx takes more than 5 seconds, kill it or something like that. Thanks in advance

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• Algorithm performance

  - by william007

  I am testing an algorithm for different parameters on a computer. I notice the performance fluctuates for each parameters. Say I run for the first time I got 20 ms, second times I got 5ms, third times I got 4ms: But the algorithm should work the same for these 3 times. I am using stopwatch from C# library to count the time, is there a better way to measure the performance without subjecting to those fluctuations?

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• Python - Is a dictionary slow to find frequency of each character?

  - by psihodelia

  I am trying to find a frequency of each symbol in any given text using an algorithm of O(n) complexity. My algorithm looks like: s = len(text) P = 1.0/s freqs = {} for char in text: try: freqs[char]+=P except: freqs[char]=P but I doubt that this dictionary-method is fast enough, because it depends on the underlying implementation of the dictionary methods. Is this the fastest method?

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• Number of 0/1 colorings of a m X n rectangle which have no monochromatic subrectangles with both dimension greater than 1.

  - by acbruptenda

  A m x n rectangular matrix is give, and each cell is to be filled with 0/1 colour. I have to find number of colorings possible so that there is no monochromatic coloured (same colour) sub-rectangle whose both dimension is greater than 1 (eg - 2x2, 2x3,4x3) I have found a slightly different version of it here But they have said nothing about the algorithm. So, I am looking for an algorithm here !!

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• What is the best way to find the period of a (repeating) list in Mathematica?

  - by Arnoud Buzing

  What is the best way to find the period in a repeating list? For example: a = {4, 5, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 1, 2} has repeat {4, 5, 1, 2, 3} with the remainder {4, 5, 1, 2} matching, but being incomplete. The algorithm should be fast enough to handle longer cases, like so: b = RandomInteger[10000, {100}]; a = Join[b, b, b, b, Take[b, 27]] The algorithm should return $Failed if there is no repeating pattern like above.

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• unique substrings using suffix tree

  - by user1708762

  For a given string S of length n- Optimal algorithm for finding all unique substrings of S can't be less than O(n^2). So, the best algorithm will give us the complexity of O(n^2). As per what I have read, this can be implemented by creating suffix tree for S. The suffix tree for S can be created in O(n) time. Now, my question is- How can we use the suffix tree for S to get all the unique substrings of S in O(n^2)?

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• SSLCipherSuite - disable weak encryption, cbc cipher and md5 based algorithm

  - by John

  A developer recently ran a PCI Scan with TripWire against our LAMP server. They identified several issues and instructed the following to correct the issues: Problem: SSL Server Supports Weak Encryption for SSLv3, TLSv1, Solution: Add the following rule to httpd.conf SSLCipherSuite ALL:!aNULL:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM Problem: SSL Server Supports CBC Ciphers for SSLv3, TLSv1 Solution: Disable any cipher suites using CBC ciphers Problem: SSL Server Supports Weak MAC Algorithm for SSLv3, TLSv1 Solution: Disable any cipher suites using MD5 based MAC algorithms I tried searching google for a comprehensive tutorial on how to construct an SSLCipherSuite directive to meet my requirements, but I didn't find anything I could understand. I see examples of SSLCipherSuite directives, but I need an explanation on what each component of the directive does. So even in the directive SSLCipherSuite ALL:!aNULL:!eNULL:!LOW:!EXP:RC4+RSA:+HIGH:+MEDIUM, I dont understand for example what the !LOW means. Can someone either a) tell me the SSLCipherSuite directive that will meet my needs or b) show me a resource that clearly explains each segment of a SSLCipherSuite is and how to construct one?

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• What is the difference between these two find algorithms? [migrated]

  - by Joe

  I have these two find algorithm which look the same to me. Can anyone help me out why they are actually different? Find ( x ) : if x.parent = x then return x else return Find ( x.parent ) vs Find ( x ) : if x.parent = x then return x else x.parent <- Find(x.parent) return x.parent I interpret the first one as int i = 0; return i++; while the second one as int i = 0; int tmp = i++; return tmp which are exactly the same to me.

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• What problems have you solved using artificial neural networks?

  - by knorv

  I'd like to know about specific problems you - the SO reader - have solved using artificial neural network techniques and what libraries/frameworks you used if you didn't roll your own. Questions: What problems have you used artificial neural networks to solve? What libraries/frameworks did you use? I'm looking for first-hand experiences, so please do not answer unless you have that.

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• Setting up java configurations in eclipse..Param files

  - by Charlie

  I'm going to be using ECJ for doing genetic programming and I haven't touched java in years. I'm working on setting up the eclipse environment and I'm catching a few snags. The ECJ source has several packages, and several sample programs come along with it. I ran one sample program (called tutorial1) by going to the run configurations and adding -file pathToParamsFile to the program arguments. This made it point to the params file of that tutorial and run that sample. In a new example I am testing (from the package gui) there are TWO params files. I tried pointing to just one param file and a program ran in the console, but there was supposed to be a GUI which did not load. I'm not sure what I'm doing wrong. Any help would be greaaatly appreciated.

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• Code bacteria: evolving mathematical behavior

  - by Stefano Borini

  It would not be my intention to put a link on my blog, but I don't have any other method to clarify what I really mean. The article is quite long, and it's in three parts (1,2,3), but if you are curious, it's worth the reading. A long time ago (5 years, at least) I programmed a python program which generated "mathematical bacteria". These bacteria are python objects with a simple opcode-based genetic code. You can feed them with a number and they return a number, according to the execution of their code. I generate their genetic codes at random, and apply an environmental selection to those objects producing a result similar to a predefined expected value. Then I let them duplicate, introduce mutations, and evolve them. The result is quite interesting, as their genetic code basically learns how to solve simple equations, even for values different for the training dataset. Now, this thing is just a toy. I had time to waste and I wanted to satisfy my curiosity. however, I assume that something, in terms of research, has been made... I am reinventing the wheel here, I hope. Are you aware of more serious attempts at creating in-silico bacteria like the one I programmed? Please note that this is not really "genetic algorithms". Genetic algorithms is when you use evolution/selection to improve a vector of parameters against a given scoring function. This is kind of different. I optimize the code, not the parameters, against a given scoring function.

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• Setting up java configurations in eclipse. multiple .param files

  - by Charlie

  I'm going to be using ECJ for doing genetic programming and I haven't touched java in years. I'm working on setting up the eclipse environment and I'm catching a few snags. The ECJ source has several packages, and several sample programs come along with it. I ran one sample program (called tutorial1) by going to the run configurations and adding -file pathToParamsFile to the program arguments. This made it point to the params file of that tutorial and run that sample. In a new example I am testing (from the package gui) there are TWO params files. I tried pointing to just one param file and a program ran in the console, but there was supposed to be a GUI which did not load. I'm not sure what I'm doing wrong. Any help would be greaaatly appreciated.

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• What algorithms do "the big ones" use to cluster news?

  - by marco92w

  I want to cluster texts for a news website. At the moment I use this algorithm to find the related articles. But I found out that PHP's similar_text() gives very good results, too. What sort of algorithms do "the big ones", Google News, Topix, Techmeme, Wikio, Megite etc., use? Of course, you don't know exactly how the algorithms work. It's secret. But maybe someone knows approximately the way they work? The algorithm I use at the moment is very slow. It only compares two articles. So for having the relations between 5,000 articles you need about 12,500,000 comparisons. This is quite a lot. Are there alternatives to reduce the number of necessary comparisons? [I don't look for improvements for my algorithm.] What do "the big ones" do? I'm sure they don't always compare one article to another and this 12,500,000 times for 5,000 news. It would be great if somebody can say something about this topic.

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• What Algorithm will Find New Longtail Keywords for *keyword* in PPC

  - by Becci

  I am looking for the algorithm (or combo) that would allow someone to find new longtail PPC search phrases based on say one corekeyword. Eg #1 word word corekeyword eg #2 word corekeyword word Google search tool allows a limited number vertically - mostly of eg#1 (https://adwords.google.com.au/select/KeywordToolExternal) I also know of other PPC apps that allow more volume than google adwords keyword tool, But I want to find other combos that mention the corekeyword & then naturally sort for the highest volume searched. Working example of exact match: corekeyword: copywriter (40,500 searches a month) google will serve up: become a copywriter (480 searches globally/month in english) But if I specifically look up: How to become a copywriter (720 searches a month) This exact longtail keyword phrase has 300 more searches than the 3 word version spat out by google. I want the algorithm to find any other highly search exact longtials like: how to become a copywriter Simply because it was save significant $ finding other longtail keywords after your campaign has been running an made google lots of money. I don't want a concantenation algorithm (I already have one of those), because hypothetically, I don't know what keywords will be that I want to find. Any gurus out there? Becci

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• looking for a license key algorithm.

  - by giulio

  There are a lot of questions relating to license keys asked on stackoverflow. But they don't answer this question. Can anyone provide a simple license key algorithm that is technology independent and doesn't required a diploma in mathematics to understand ? The license key algorithm is similar to public key encryption. I just need something simple that can be implemented in any platform .Net/Java and uses simple data like characters. Preferably no byte translations required. So if a person presents a string, a complementary string can be generated that is the authorisation code. Below is a common scenario that it would be used for. Customer downloads s/w which generates a unique key upon initial startup/installation. S/w runs during trial period. At end of trial period an authorisation key is required. Customer goes to designated web-site, enters their code and get authorisation code to enable s/w, after paying :) Don't be afraid to describe your answer as though you're talking to a 5 yr old as I am not a mathemtician. Just need a decent basic algorithm, we're not launching nukes... NB: Please no philosophy on encryption nor who is Diffie-Hellman. I just need a basic solution.

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