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• How well do zippers perform in practice, and when should they be used?

  - by Rob

  I think that the zipper is a beautiful idea; it elegantly provides a way to walk a list or tree and make what appear to be local updates in a functional way. Asymptotically, the costs appear to be reasonable. But traversing the data structure requires memory allocation at each iteration, where a normal list or tree traversal is just pointer chasing. This seems expensive (please correct me if I am wrong). Are the costs prohibitive? And what under what circumstances would it be reasonable to use a zipper?

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• WCF, 4.0, Bidirectional...

  - by TomTom

  ...what options are there now with .NET 4.0, in a way that does support NAT for the client side (i.e. client behind NAT). I would prefer to use something HTTP based, but that is a weak condition - I think mid term I will have some non http communication outside WCF anyway, so proxy traversal is something I could delay. Pre .NET 4.0 there was the issue that basically the server-client channel would be opened from the server, which made NAT something non-traversable. Polling is not acceptable - we talk time sensitive information here. So, what are my options now?

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• How can I traverse the EMF object tree generated by Xtext?

  - by reprogrammer

  I'm using Xtext to define my DSL. Xtext generates a parser that lets me traverse the EMF model of my input DSL. I'd like to translate this EMF model into some other tree. To do this translation, I need to traverse the tree. But, I couldn't find a visitor class for the EMF model generated by Xtext. The closest thing that I've found is a Switch class that visits a single node. I can traverse the EMF model myself and invoke the Switch class on each node that I visit. But, I wonder if there exists a visitor functionality in Xtext that implements the model traversal.

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• How to get a reference to node in DOM tree in Google Chrome debugger console

  - by .yahoo.co.jpaqwsykcj3aulh3h1k0cy6nzs3isj

  In the Google Chrome debugger, I often want to get a reference to a node in the DOM tree. I can click the "magnifying glass" button and then click the desired element in the browser window to select the corresponding node in the DOM tree displayed in the debugger. But how can I get a reference to that node in the console? If the element has an id, document.getElementById works, but if there is no id, is there a better alternative to XPath or manual traversal of the DOM tree using children? In case XPath is the best way, is there a better way than doing something like this: var evaluator = new XPathEvaluator(); var result = evaluator.evaluate("//div", document.documentElement, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null); which is a pain to type out each time.

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• iPad/iPhone: Form filling application pointers

  - by raj.tiwari

  Folks, I am starting work on an iPad/iPhone application that is essentially a form-filing UI. The requirement is to present a (rather large) form to the user. The form is composed of sections and questions, like so: Form Question 0.1 Question 0.2 Section 1 Question 1.1 etc. The user can take various paths down the form based on answers to questions. I would like to architect this by defining a declarative markup that can be used to author the form questionnaire including traversal rules. My questions are: Can anyone recommend a markup/language that would satisfy the declaration requirement? Is there any existing library that would ease the implementation as described above? Thanks for your time.

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• Help with Btree homework

  - by Phenom

  I need to do a preorder traversal of a Btree, and among other things, print the following information for each page (which is the same thing as a node): The B-Tree page number The value of each B-Tree page pointer (e.g., address, byte offset, RRN). My questions are: 1. How do you figure out the byte offset? What is it offset from? 2. Isn't the RRN the same as the page number? Note: A Btree is NOT A BINARY TREE. Btrees can have multiple keys in each node, and a node with n keys has n+1 child pointers.

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• Finding the heaviest length-constrained path in a weighted Binary Tree

  - by Hristo

  UPDATE I worked out an algorithm that I think runs in O(n*k) running time. Below is the pseudo-code: routine heaviestKPath( T, k ) // create 2D matrix with n rows and k columns with each element = -8 // we make it size k+1 because the 0th column must be all 0s for a later // function to work properly and simplicity in our algorithm matrix = new array[ T.getVertexCount() ][ k + 1 ] (-8); // set all elements in the first column of this matrix = 0 matrix[ n ][ 0 ] = 0; // fill our matrix by traversing the tree traverseToFillMatrix( T.root, k ); // consider a path that would arc over a node globalMaxWeight = -8; findArcs( T.root, k ); return globalMaxWeight end routine // node = the current node; k = the path length; node.lc = node’s left child; // node.rc = node’s right child; node.idx = node’s index (row) in the matrix; // node.lc.wt/node.rc.wt = weight of the edge to left/right child; routine traverseToFillMatrix( node, k ) if (node == null) return; traverseToFillMatrix(node.lc, k ); // recurse left traverseToFillMatrix(node.rc, k ); // recurse right // in the case that a left/right child doesn’t exist, or both, // let’s assume the code is smart enough to handle these cases matrix[ node.idx ][ 1 ] = max( node.lc.wt, node.rc.wt ); for i = 2 to k { // max returns the heavier of the 2 paths matrix[node.idx][i] = max( matrix[node.lc.idx][i-1] + node.lc.wt, matrix[node.rc.idx][i-1] + node.rc.wt); } end routine // node = the current node, k = the path length routine findArcs( node, k ) if (node == null) return; nodeMax = matrix[node.idx][k]; longPath = path[node.idx][k]; i = 1; j = k-1; while ( i+j == k AND i < k ) { left = node.lc.wt + matrix[node.lc.idx][i-1]; right = node.rc.wt + matrix[node.rc.idx][j-1]; if ( left + right > nodeMax ) { nodeMax = left + right; } i++; j--; } // if this node’s max weight is larger than the global max weight, update if ( globalMaxWeight < nodeMax ) { globalMaxWeight = nodeMax; } findArcs( node.lc, k ); // recurse left findArcs( node.rc, k ); // recurse right end routine Let me know what you think. Feedback is welcome. I think have come up with two naive algorithms that find the heaviest length-constrained path in a weighted Binary Tree. Firstly, the description of the algorithm is as follows: given an n-vertex Binary Tree with weighted edges and some value k, find the heaviest path of length k. For both algorithms, I'll need a reference to all vertices so I'll just do a simple traversal of the Tree to have a reference to all vertices, with each vertex having a reference to its left, right, and parent nodes in the tree. Algorithm 1 For this algorithm, I'm basically planning on running DFS from each node in the Tree, with consideration to the fixed path length. In addition, since the path I'm looking for has the potential of going from left subtree to root to right subtree, I will have to consider 3 choices at each node. But this will result in a O(n*3^k) algorithm and I don't like that. Algorithm 2 I'm essentially thinking about using a modified version of Dijkstra's Algorithm in order to consider a fixed path length. Since I'm looking for heaviest and Dijkstra's Algorithm finds the lightest, I'm planning on negating all edge weights before starting the traversal. Actually... this doesn't make sense since I'd have to run Dijkstra's on each node and that doesn't seem very efficient much better than the above algorithm. So I guess my main questions are several. Firstly, do the algorithms I've described above solve the problem at hand? I'm not totally certain the Dijkstra's version will work as Dijkstra's is meant for positive edge values. Now, I am sure there exist more clever/efficient algorithms for this... what is a better algorithm? I've read about "Using spine decompositions to efficiently solve the length-constrained heaviest path problem for trees" but that is really complicated and I don't understand it at all. Are there other algorithms that tackle this problem, maybe not as efficiently as spine decomposition but easier to understand? Thanks.

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• How to Serialize Binary Tree

  - by Veljko Skarich

  I went to an interview today where I was asked to serialize a binary tree. I implemented an array-based approach where the children of node i (numbering in level-order traversal) were at the 2*i index for the left child and 2*i + 1 for the right child. The interviewer seemed more or less pleased, but I'm wondering what serialize means exactly? Does it specifically pertain to flattening the tree for writing to disk, or would serializing a tree also include just turning the tree into a linked list, say. Also, how would we go about flattening the tree into a (doubly) linked list, and then reconstructing it? Can you recreate the exact structure of the tree from the linked list? Thank you/

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• how to exploit vulnerability of php?

  - by Dr Deo

  i have never seen a buffer overflow exploit in live action. supporse I have found a server that seems to have vulnerabilities. Where can i get proof of the concept code preferably in c/c++ to exploit the vulnerability? eg i found this vulnerability Multiple directory traversal vulnerabilities in functions such as 'posix_access()', 'chdir()', 'ftok()' may allow a remote attacker to bypass 'safe_mode' restrictions. (CVE-2008-2665 and CVE-2008-2666). How can i get proof of concept code for educational purposes PS I am a student and my only desire is to learn

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• Any tips of how to handle hierarchical trees in relational model?

  - by George

  Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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• What's the best way to apply a drop shadow?

  - by jckeyes

  What is the best method for applying drop shadows? I'm working on a site right now where we have a good deal of them, however, I've been fighting to find the best method to do it. The site is pretty animation heavy so shadows need to work well with this. I tried a jQuery shadow pulgin. The shadows looked good and were easy to use but were slow and didn't work well with any animations (required lots of redrawing, very joggy). I also tried creating my own jQuery extension that wraps my element in a couple gray divs and then offsets them a little bit to give a shadow effect. This worked well. It's quick and responsive to the animation. However, it makes DOM manipulation/traversal cumbersome since everything is wrapped in these shadow divs. I know there has to be a better way but this isn't exactly my forte. Thoughts?

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• Internet explore is unresponsive while loading a large page

  - by kdhamane

  We have a html page being rendered in the browser (IE) that causes the browser to hang. The page is generated through server side script (ASP.NET and viewstate is disabled). The page while loading takes a long time (its not a b\w issue since we can reproduce it on local machine) and sometimes results in script unresponsive error. On debugging the issue we found that the html size on the client side is 4.73 MB. There's also a lot of DOM traversal (using JQuery) after document is ready (jquery-document.ready). After loading as well, the page simply hangs on any user interaction (scroll, mouseover) etc. A CPU usage spike (25-50% usage) is seen during loading and on any user interaction

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• assignment vs std::swap and merging and keeping duplicates in seperate object

  - by rubenvb

  Say I have two std::set<std::string>s. The first one, old_options, needs to be merged with additional options, contained in new_options. I can't just use std::merge (well, I do, but not only that) because I also check for doubles and warn the user about this accordingly. To this effect, I have void merge_options( set<string> &old_options, const set<string> &new_options ) { // find duplicates and create merged_options, a stringset containing the merged options // handle duplicated the way I want to // ... old_options = merged_options; } Is it better to use std::swap( merged_options, old_options ); or the assignment I have? Is there a better way to filter duplicates and return the merged set than consecutive calls to std::set_intersection and std::set_union to detect dupes and merge the sets? I know it's slower than one traversal and doing both at once, but these sets are small (performance is not critical) and I trust the Standard more than I trust myself.

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• Getting a table's values into a tree

  - by Jason

  So, I have a table like such: id|root|kw1|kw2|kw3|kw4|kw5|name 1| A| B| C| D| E| F|fileA 2| A| B| | | | |fileB 3| B| C| D| E| | |fileC 4| A| B| | | | |fileD (several hundred rows...) And I need to get it into a tree like the following: *A *B -fileB -fileD *C *D *E *F -fileA *B *C *D *E -fileC I'm pretty sure the table is laid out poorly but it's what I have to live with. I've read a little about Adjacency List Model & Modified Preorder Tree Traversal but I don't think my data is laid out correctly. I think this requires a recursive function, but I'm not at all sure how to go about that. I'm open to any ideas of how to get this done even if it means extracting the data into a new table just to process this. Are there any good options available to me or any good ways to do this? (Examples are a bonus of course)

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• In Scala 2.8 collections, why was the Traversable type added above Iterable?

  - by Seth Tisue

  I know that to be Traversable, you need only have a foreach method. Iterable requires an iterator method. Both the Scala 2.8 collections SID and the "Fighting Bitrot with Types" paper are basically silent on the subject of why Traversable was added. The SID only says "David McIver... proposed Traversable as a generalization of Iterable." I have vaguely gathered from discussions on IRC that it has to do with reclaiming resources when traversal of a collection terminates? The following is probably related to my question. There are some odd-looking function definitions in TraversableLike.scala, for example: def isEmpty: Boolean = { var result = true breakable { for (x <- this) { result = false break } } result } I assume there's a good reason that wasn't just written as: def isEmpty: Boolean = { for (x <- this) return false true }

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• Any tips of how to handle hierarchial trees in relational model?

  - by George

  Hello all. I have a tree structure that can be n-levels deep, without restriction. That means that each node can have another n nodes. What is the best way to retrieve a tree like that without issuing thousands of queries to the database? I looked at a few other models, like flat table model, Preorder Tree Traversal Algorithm, and so. Do you guys have any tips or suggestions of how to implement a efficient tree model? My objective in the real end is to have one or two queries that would spit the whole tree for me. With enough processing i can display the tree in dot net, but that would be in client machine, so, not much of a big deal. Thanks for the attention

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• The risk of granting to IUSR* NTFS permissions on a folder on the server

  - by vtortola

  I have two web applications that must share a file in the server file system. Both apps are inside of "Inetpub\wwwroot". The file cannot be accessed freely from outside, so it is in a folder out of "Inetpub". I have granted full NTFS permissions to the user "IUSR_whatever" (is the user that runs IIS in anonymous requests) in that folder. The folder has only that file, and has no other use. It works so far :) But, what is the risk? what should I be afraid of? As I see it, as long the folder is out of the "InetPub" cannot be accessed, and as long the apps don't have any security flaw like "path traversal" or server side code injection, it should be safe enough.... But I'm always keen to be wrong :) What do you think? May the file or even the server itself get compromised because of this? Thanks.

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• java - Depth First Search - Perform DFS on a tree

  - by DJDonaL3000

  Im trying to perform DFS on a Minimum Spanning Tree which contains 26 nodes. Nodes are named 'A' to 'Z' and the tree is undirected. I have an empty function called DFS here that I am trying to write, which (i presume) takes in the tree (a 2D array) a startNode (randomly selected node 'M') and the endNode (randomly selected node 'Z'). The weights of connected nodes are identified in the 2D array parameter, but how do I actually get started visiting nodes? All that is required is to print each nodeName in the order of the DFS traversal. Do I need to create a Node_class for each node in the 2d array??

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• Prevent "jQuery( html )" from triggering the browser to request images and other referenced content

  - by Chris Dutrow

  Using jQuery to create new DOM elements from text. Example: jQuery('<div><img src="/some_image.gif"></img></div>'); When this statement is executed, it causes the browser to request the file 'some_img.gif' from the server. Is there a way to execute this statement so that the resulting jQuery object can be used from DOM traversal, but not actually cause the browser to hit the server with requests for images and other referenced content? Example: var jquery_elememnts = jQuery('<div><img class="a_class" src="/some_image.gif"></img></div>'); var img_class = jquery_elememnts.find('img').attr('class'); The only idea I have now is to use regex to remove all of the 'src' tags from image elements and other things that will trigger the browser requests before using jQuery to evaluate the HTML. How can jQuery be used to evaluate HTML without triggering the browser to make requests to the server for referenced content inside the evaluated HTML? Thanks!

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• Use CSS Selectors with HtmlUnit

  - by kerry

  HtmlUnit is a great library for performing web integration tests in Java.  But sometimes node traversal can be somewhat cumbersome. Fear not fellow automated tester (good for you!).  I found a great little project on Github that will allow you to query your document for elements via css selectors similar to jQuery. The project is located at https://github.com/chrsan/css-selectors.  You can use Maven to build it, or download 1.0.2 here.  Beware.  I will not be updating this link so I suggest you download the latest code. In any case, you can use it like so: // from HtmlUnit getting started final WebClient webClient = new WebClient(); final HtmlPage page = webClient.getPage("http://htmlunit.sourceforge.net"); final DOMNodeSelector cssSelector = new DOMNodeSelector(page.getDocumentElement()); final Set elements = cssSelector.querySelectorAll("div.section h2"); final Node first = elements.iterator().next(); assertThat(first.getTextContent(), equalTo("HtmlUnit")); The only problem here is that the querySelectAll returns a Set<Node>.  Not HtmlElement like we may want in some cases.   However, if you were to reflect on the Set, you would find that it is indeed a Set of HtmlElement objects. Typically, I like to create a base class for my web tests.  Just for fun, I am using the $ method similar to jQuery. public class WebTestBase { protected WebClient webClient; protected HtmlPage htmlPage; protected void goTo(final String url){ return (HtmlPage)webClient.getPage(url); } protected List $(final String cssSelector) { final DOMNodeSelector cssSelector = new DOMNodeSelector(htmlPage.getDocumentElement()); final Set nodes = cssSelector.querySelectorAll("div.section h2"); // for some reason Set cannot be cast to Set? final List elements = new ArrayList(nodes.size()); for (final Node node : nodes) { elements.add((HtmlElement)node); } return elements; } } Now we can write tests like this: public class LoginWebTest extends WebTestBase { @Test public void login_page_has_instructions() throws Exception { goTo(baseUrl + "/login") assertThat( $("p.instructions").size(), equalTo(1) ); } }

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• What Precalculus knowledge is required before learning Discrete Math Computer Science topics?

  - by Ein Doofus

  Below I've listed the chapters from a Precalculus book as well as the author recommended Computer Science chapters from a Discrete Mathematics book. Although these chapters are from two specific books on these subjects I believe the topics are generally the same between any Precalc or Discrete Math book. What Precalculus topics should one know before starting these Discrete Math Computer Science topics?: Discrete Mathematics CS Chapters 1.1 Propositional Logic 1.2 Propositional Equivalences 1.3 Predicates and Quantifiers 1.4 Nested Quantifiers 1.5 Rules of Inference 1.6 Introduction to Proofs 1.7 Proof Methods and Strategy 2.1 Sets 2.2 Set Operations 2.3 Functions 2.4 Sequences and Summations 3.1 Algorithms 3.2 The Growths of Functions 3.3 Complexity of Algorithms 3.4 The Integers and Division 3.5 Primes and Greatest Common Divisors 3.6 Integers and Algorithms 3.8 Matrices 4.1 Mathematical Induction 4.2 Strong Induction and Well-Ordering 4.3 Recursive Definitions and Structural Induction 4.4 Recursive Algorithms 4.5 Program Correctness 5.1 The Basics of Counting 5.2 The Pigeonhole Principle 5.3 Permutations and Combinations 5.6 Generating Permutations and Combinations 6.1 An Introduction to Discrete Probability 6.4 Expected Value and Variance 7.1 Recurrence Relations 7.3 Divide-and-Conquer Algorithms and Recurrence Relations 7.5 Inclusion-Exclusion 8.1 Relations and Their Properties 8.2 n-ary Relations and Their Applications 8.3 Representing Relations 8.5 Equivalence Relations 9.1 Graphs and Graph Models 9.2 Graph Terminology and Special Types of Graphs 9.3 Representing Graphs and Graph Isomorphism 9.4 Connectivity 9.5 Euler and Hamilton Ptahs 10.1 Introduction to Trees 10.2 Application of Trees 10.3 Tree Traversal 11.1 Boolean Functions 11.2 Representing Boolean Functions 11.3 Logic Gates 11.4 Minimization of Circuits 12.1 Language and Grammars 12.2 Finite-State Machines with Output 12.3 Finite-State Machines with No Output 12.4 Language Recognition 12.5 Turing Machines Precalculus Chapters R.1 The Real-Number System R.2 Integer Exponents, Scientific Notation, and Order of Operations R.3 Addition, Subtraction, and Multiplication of Polynomials R.4 Factoring R.5 Rational Expressions R.6 Radical Notation and Rational Exponents R.7 The Basics of Equation Solving 1.1 Functions, Graphs, Graphers 1.2 Linear Functions, Slope, and Applications 1.3 Modeling: Data Analysis, Curve Fitting, and Linear Regression 1.4 More on Functions 1.5 Symmetry and Transformations 1.6 Variation and Applications 1.7 Distance, Midpoints, and Circles 2.1 Zeros of Linear Functions and Models 2.2 The Complex Numbers 2.3 Zeros of Quadratic Functions and Models 2.4 Analyzing Graphs of Quadratic Functions 2.5 Modeling: Data Analysis, Curve Fitting, and Quadratic Regression 2.6 Zeros and More Equation Solving 2.7 Solving Inequalities 3.1 Polynomial Functions and Modeling 3.2 Polynomial Division; The Remainder and Factor Theorems 3.3 Theorems about Zeros of Polynomial Functions 3.4 Rational Functions 3.5 Polynomial and Rational Inequalities 4.1 Composite and Inverse Functions 4.2 Exponential Functions and Graphs 4.3 Logarithmic Functions and Graphs 4.4 Properties of Logarithmic Functions 4.5 Solving Exponential and Logarithmic Equations 4.6 Applications and Models: Growth and Decay 5.1 Systems of Equations in Two Variables 5.2 System of Equations in Three Variables 5.3 Matrices and Systems of Equations 5.4 Matrix Operations 5.5 Inverses of Matrices 5.6 System of Inequalities and Linear Programming 5.7 Partial Fractions 6.1 The Parabola 6.2 The Circle and Ellipse 6.3 The Hyperbola 6.4 Nonlinear Systems of Equations

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• Asynchronously returning a hierarchal data using .NET TPL... what should my return object "look" like?

  - by makerofthings7

  I want to use the .NET TPL to asynchronously do a DIR /S and search each subdirectory on a hard drive, and want to search for a word in each file... what should my API look like? In this scenario I know that each sub directory will have 0..10000 files or 0...10000 directories. I know the tree is unbalanced and want to return data (in relation to its position in the hierarchy) as soon as it's available. I am interested in getting data as quickly as possible, but also want to update that result if "better" data is found (better means closer to the root of c:) I may also be interested in finding all matches in relation to its position in the hierarchy. (akin to a report) Question: How should I return data to my caller? My first guess is that I think I need a shared object that will maintain the current "status" of the traversal (started | notstarted | complete ) , and might base it on the System.Collections.Concurrent. Another idea that I'm considering is the consumer/producer pattern (which ConcurrentCollections can handle) however I'm not sure what the objects "look" like. Optional Logical Constraint: The API doesn't have to address this, but in my "real world" design, if a directory has files, then only one file will ever contain the word I'm looking for.  If someone were to literally do a DIR /S as described above then they would need to account for more than one matching file per subdirectory. More information : I'm using Azure Tables to store a hierarchy of data using these TPL extension methods. A "node" is a table. Not only does each node in the hierarchy have a relation to any number of nodes, but it's possible for each node to have a reciprocal link back to any other node. This may have issues with recursion but I'm addressing that with a shared object in my recursion loop. Note that each "node" also has the ability to store local data unique to that node. It is this information that I'm searching for. In other words, I'm searching for a specific fixed RowKey in a hierarchy of nodes. When I search for the fixed RowKey in the hierarchy I'm interested in getting the results FAST (first node found) but prefer data that is "closer" to the starting point of the hierarchy. Since many nodes may have the particular RowKey I'm interested in, sometimes I may want to get a report of ALL the nodes that contain this RowKey.

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• How can I tweak this A* search pathfinding algorithm to handle different terrain movement values?

  - by user422318

  I'm creating a 2D map-based action game with similar interaction design as Diablo II. In other words, the player clicks around a map to move their player. I just finished player movement and am moving on to pathfinding. In the game, enemies should charge the player's character. There are also five different terrain types that give different movement bonuses. I want the AI to take advantage of these terrain bonuses as they try to reach the player. I was told to check out the A* search algorithm (http://en.wikipedia.org/wiki/A*_search_algorithm). I'm doing this game in HTML5 and JavaScript, and found a version in JavaScript: http://www.briangrinstead.com/blog/astar-search-algorithm-in-javascript I'm trying to figure out how to tweak it though. Below are my ideas about what I need to change. What else do I need to worry about? When I create a graph, I will need to initialize the 2D array I pass in passed on with a traversal of a map that corresponds to the different terrain types. in graph.js: "GraphNodeType" definition needs to be modified to handle the 5 terrain types. There will be no walls. in astar.js: The g and h scoring will need to be modified. How should I do this? in astar.js: isWall() should probably be removed. My game doesn't have walls. in astar.js: I'm not sure what this is. I think it indicates a node that isn't valid to be processed. When would this happen, though? At a high level, how do I change this algorithm from "oh, is there a wall there?" to "will this terrain get me to the player faster than the terrain around me?" Because of time, I'm also debating reusing my Bresenham algorithm for the enemies. Unfortunately, the different terrain movement bonuses won't be used by the AI, which will make the game suck. :/ I'd really like to have this in for the prototype, but I'm not a developer by trade nor am I a computer scientist. :D If you know of any code that does what I'm looking for, please share! Sanity check tips for this are also appreciated.

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• Why are MVC & TDD not employed more in game architecture?

  - by secoif

  I will preface this by saying I haven't looked a huge amount of game source, nor built much in the way of games. But coming from trying to employ 'enterprise' coding practices in web apps, looking at game source code seriously hurts my head: "What is this view logic doing in with business logic? this needs refactoring... so does this, refactor, refactorrr" This worries me as I'm about to start a game project, and I'm not sure whether trying to mvc/tdd the dev process is going to hinder us or help us, as I don't see many game examples that use this or much push for better architectural practices it in the community. The following is an extract from a great article on prototyping games, though to me it seemed exactly the attitude many game devs seem to use when writing production game code: Mistake #4: Building a system, not a game ...if you ever find yourself working on something that isn’t directly moving your forward, stop right there. As programmers, we have a tendency to try to generalize our code, and make it elegant and be able to handle every situation. We find that an itch terribly hard not scratch, but we need to learn how. It took me many years to realize that it’s not about the code, it’s about the game you ship in the end. Don’t write an elegant game component system, skip the editor completely and hardwire the state in code, avoid the data-driven, self-parsing, XML craziness, and just code the damned thing. ... Just get stuff on the screen as quickly as you can. And don’t ever, ever, use the argument “if we take some extra time and do this the right way, we can reuse it in the game”. EVER. is it because games are (mostly) visually oriented so it makes sense that the code will be weighted heavily in the view, thus any benefits from moving stuff out to models/controllers, is fairly minimal, so why bother? I've heard the argument that MVC introduces a performance overhead, but this seems to me to be a premature optimisation, and that there'd more important performance issues to tackle before you worry about MVC overheads (eg render pipeline, AI algorithms, datastructure traversal, etc). Same thing regarding TDD. It's not often I see games employing test cases, but perhaps this is due to the design issues above (mixed view/business) and the fact that it's difficult to test visual components, or components that rely on probablistic results (eg operate within physics simulations). Perhaps I'm just looking at the wrong source code, but why do we not see more of these 'enterprise' practices employed in game design? Are games really so different in their requirements, or is a people/culture issue (ie game devs come from a different background and thus have different coding habits)?

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• Setup VPN issue on Ubuntu Server 12.04

  - by Yozone W.

  I have a problem with setup VPN server on my Ubuntu VPS, here is my server environments: Ubuntu Server 12.04 x86_64 xl2tpd 1.3.1+dfsg-1 pppd 2.4.5-5ubuntu1 openswan 1:2.6.38-1~precise1 After install software and configuration: ipsec verify Checking your system to see if IPsec got installed and started correctly: Version check and ipsec on-path [OK] Linux Openswan U2.6.38/K3.2.0-24-virtual (netkey) Checking for IPsec support in kernel [OK] SAref kernel support [N/A] NETKEY: Testing XFRM related proc values [OK] [OK] [OK] Checking that pluto is running [OK] Pluto listening for IKE on udp 500 [OK] Pluto listening for NAT-T on udp 4500 [OK] Checking for 'ip' command [OK] Checking /bin/sh is not /bin/dash [WARNING] Checking for 'iptables' command [OK] Opportunistic Encryption Support [DISABLED] /var/log/auth.log message: Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [RFC 3947] method set to=115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike] meth=114, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-08] meth=113, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-07] meth=112, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-06] meth=111, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-05] meth=110, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-04] meth=109, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-03] meth=108, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02] meth=107, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [draft-ietf-ipsec-nat-t-ike-02_n] meth=106, but already using method 115 Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: ignoring Vendor ID payload [FRAGMENTATION 80000000] Oct 16 06:50:54 vpn pluto[3963]: packet from [My IP Address]:2251: received Vendor ID payload [Dead Peer Detection] Oct 16 06:50:54 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: responding to Main Mode from unknown peer [My IP Address] Oct 16 06:50:54 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: transition from state STATE_MAIN_R0 to state STATE_MAIN_R1 Oct 16 06:50:54 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: STATE_MAIN_R1: sent MR1, expecting MI2 Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: NAT-Traversal: Result using draft-ietf-ipsec-nat-t-ike (MacOS X): peer is NATed Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: transition from state STATE_MAIN_R1 to state STATE_MAIN_R2 Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: STATE_MAIN_R2: sent MR2, expecting MI3 Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: ignoring informational payload, type IPSEC_INITIAL_CONTACT msgid=00000000 Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: Main mode peer ID is ID_IPV4_ADDR: '192.168.12.52' Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[5] [My IP Address] #5: switched from "L2TP-PSK-NAT" to "L2TP-PSK-NAT" Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: deleting connection "L2TP-PSK-NAT" instance with peer [My IP Address] {isakmp=#0/ipsec=#0} Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: transition from state STATE_MAIN_R2 to state STATE_MAIN_R3 Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: new NAT mapping for #5, was [My IP Address]:2251, now [My IP Address]:2847 Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: STATE_MAIN_R3: sent MR3, ISAKMP SA established {auth=OAKLEY_PRESHARED_KEY cipher=aes_256 prf=oakley_sha group=modp1024} Oct 16 06:50:55 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: Dead Peer Detection (RFC 3706): enabled Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: the peer proposed: [My Server IP Address]/32:17/1701 -> 192.168.12.52/32:17/0 Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: NAT-Traversal: received 2 NAT-OA. using first, ignoring others Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: responding to Quick Mode proposal {msgid:8579b1fb} Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: us: [My Server IP Address]<[My Server IP Address]>:17/1701 Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: them: [My IP Address][192.168.12.52]:17/65280===192.168.12.52/32 Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: transition from state STATE_QUICK_R0 to state STATE_QUICK_R1 Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: STATE_QUICK_R1: sent QR1, inbound IPsec SA installed, expecting QI2 Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: Dead Peer Detection (RFC 3706): enabled Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: transition from state STATE_QUICK_R1 to state STATE_QUICK_R2 Oct 16 06:50:56 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #6: STATE_QUICK_R2: IPsec SA established transport mode {ESP=>0x08bda158 <0x4920a374 xfrm=AES_256-HMAC_SHA1 NATOA=192.168.12.52 NATD=[My IP Address]:2847 DPD=enabled} Oct 16 06:51:16 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: received Delete SA(0x08bda158) payload: deleting IPSEC State #6 Oct 16 06:51:16 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: ERROR: netlink XFRM_MSG_DELPOLICY response for flow eroute_connection delete included errno 2: No such file or directory Oct 16 06:51:16 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: received and ignored informational message Oct 16 06:51:16 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address] #5: received Delete SA payload: deleting ISAKMP State #5 Oct 16 06:51:16 vpn pluto[3963]: "L2TP-PSK-NAT"[6] [My IP Address]: deleting connection "L2TP-PSK-NAT" instance with peer [My IP Address] {isakmp=#0/ipsec=#0} Oct 16 06:51:16 vpn pluto[3963]: packet from [My IP Address]:2847: received and ignored informational message xl2tpd -D message: xl2tpd[4289]: Enabling IPsec SAref processing for L2TP transport mode SAs xl2tpd[4289]: IPsec SAref does not work with L2TP kernel mode yet, enabling forceuserspace=yes xl2tpd[4289]: setsockopt recvref[30]: Protocol not available xl2tpd[4289]: This binary does not support kernel L2TP. xl2tpd[4289]: xl2tpd version xl2tpd-1.3.1 started on vpn.netools.me PID:4289 xl2tpd[4289]: Written by Mark Spencer, Copyright (C) 1998, Adtran, Inc. xl2tpd[4289]: Forked by Scott Balmos and David Stipp, (C) 2001 xl2tpd[4289]: Inherited by Jeff McAdams, (C) 2002 xl2tpd[4289]: Forked again by Xelerance (www.xelerance.com) (C) 2006 xl2tpd[4289]: Listening on IP address [My Server IP Address], port 1701 Then it just stopped here, and have no any response. I can't connect VPN on my mac client, the /var/log/system.log message: Oct 16 15:17:36 azone-iMac.local configd[17]: SCNC: start, triggered by SystemUIServer, type L2TP, status 0 Oct 16 15:17:36 azone-iMac.local pppd[3799]: pppd 2.4.2 (Apple version 596.13) started by azone, uid 501 Oct 16 15:17:38 azone-iMac.local pppd[3799]: L2TP connecting to server 'vpn.netools.me' ([My Server IP Address])... Oct 16 15:17:38 azone-iMac.local pppd[3799]: IPSec connection started Oct 16 15:17:38 azone-iMac.local racoon[359]: Connecting. Oct 16 15:17:38 azone-iMac.local racoon[359]: IPSec Phase1 started (Initiated by me). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKE Packet: transmit success. (Initiator, Main-Mode message 1). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKE Packet: receive success. (Initiator, Main-Mode message 2). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKE Packet: transmit success. (Initiator, Main-Mode message 3). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKE Packet: receive success. (Initiator, Main-Mode message 4). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKE Packet: transmit success. (Initiator, Main-Mode message 5). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKEv1 Phase1 AUTH: success. (Initiator, Main-Mode Message 6). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKE Packet: receive success. (Initiator, Main-Mode message 6). Oct 16 15:17:38 azone-iMac.local racoon[359]: IKEv1 Phase1 Initiator: success. (Initiator, Main-Mode). Oct 16 15:17:38 azone-iMac.local racoon[359]: IPSec Phase1 established (Initiated by me). Oct 16 15:17:39 azone-iMac.local racoon[359]: IPSec Phase2 started (Initiated by me). Oct 16 15:17:39 azone-iMac.local racoon[359]: IKE Packet: transmit success. (Initiator, Quick-Mode message 1). Oct 16 15:17:39 azone-iMac.local racoon[359]: IKE Packet: receive success. (Initiator, Quick-Mode message 2). Oct 16 15:17:39 azone-iMac.local racoon[359]: IKE Packet: transmit success. (Initiator, Quick-Mode message 3). Oct 16 15:17:39 azone-iMac.local racoon[359]: IKEv1 Phase2 Initiator: success. (Initiator, Quick-Mode). Oct 16 15:17:39 azone-iMac.local racoon[359]: IPSec Phase2 established (Initiated by me). Oct 16 15:17:39 azone-iMac.local pppd[3799]: IPSec connection established Oct 16 15:17:59 azone-iMac.local pppd[3799]: L2TP cannot connect to the server Oct 16 15:17:59 azone-iMac.local racoon[359]: IPSec disconnecting from server [My Server IP Address] Oct 16 15:17:59 azone-iMac.local racoon[359]: IKE Packet: transmit success. (Information message). Oct 16 15:17:59 azone-iMac.local racoon[359]: IKEv1 Information-Notice: transmit success. (Delete IPSEC-SA). Oct 16 15:17:59 azone-iMac.local racoon[359]: IKE Packet: transmit success. (Information message). Oct 16 15:17:59 azone-iMac.local racoon[359]: IKEv1 Information-Notice: transmit success. (Delete ISAKMP-SA). Anyone help? Thanks a million!

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