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  • Is there a library that can decompile a method into an Expression tree, with support for CLR 4.0?

    - by Daniel Earwicker
    Previous questions have asked if it is possible to turn compiled delegates into expression trees, for example: http://stackoverflow.com/questions/767733/converting-a-net-funct-to-a-net-expressionfunct The sane answers at the time were: It's possible, but very hard and there's no standard library solution. Use Reflector! But fortunately there are some greatly-insane/insanely-great people out there who like reverse engineering things, and they make difficult things easy for the rest of us. Clearly it is possible to decompile IL to C#, as Reflector does it, and so you could in principle instead target CLR 4.0 expression trees with support for all statement types. This is interesting because it wouldn't matter if the compiler's built-in special support for Expression<> lambdas is never extended to support building statement expression trees in the compiler. A library solution could fill the gap. We would then have a high-level starting point for writing aspect-like manipulations of code without having to mess with raw IL. As noted in the answers to the above linked question, there are some promising signs but I haven't succeeded in finding if there's been much progress since by searching. So has anyone finished this job, or got very far with it? Note: CLR 4.0 is now released. Time for another look-see.

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  • Can LINQ expression classes implement the observer pattern instead of deferred execution?

    - by Tormod
    Hi. We have issues within an application using a state machine. The application is implemented as a windows service and is iteration based (it "foreaches" itself through everything) and there are myriads of instances being processed by the state machine. As I'm reading the MEAP version of Jon Skeets book "C# in Depth, 2nd ed", I'm wondering if I can change the whole thing to use linq expression instances so that guards and conditions are represented using expression trees. We are building many applications on this state machine engine and would probably greatly benefit from the new Expression tree visualizer in VS 2010 Now, simple example. If I have an expression tree where there is an OR Expression condition with two sub nodes, is there any way that these can implement the observer pattern so that the expression tree becomes event driven? If a condition change, it should notify its parent node (the OR node). Since the OR node then changes from "false" to "true", then it should notify ITS parent and so on. I love the declarative model of expression trees, but the deferred execution model works in opposite direction of the control flow if you want event based "live" conditions. Am I off on a wild goose chase here? Or is there some concept in the BCL that may help me achieve this?

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  • Generate dynamic UPDATE command from Expression<Func<T, T>>

    - by Rui Jarimba
    I'm trying to generate an UPDATE command based on Expression trees (for a batch update). Assuming the following UPDATE command: UPDATE Product SET ProductTypeId = 123, ProcessAttempts = ProcessAttempts + 1 For an expression like this: Expression<Func<Product, Product>> updateExpression = entity => new Product() { ProductTypeId = 123, ProcessAttempts = entity.ProcessAttempts + 1 }; How can I generate the SET part of the command? SET ProductTypeId = 123, ProcessAttempts = ProcessAttempts + 1

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  • Real world examples of tree structures

    - by Arec Barrwin
    I'm looking for some examples of tree structures that are used in commercial/free software projects, modern or old. I can see examples on wikipedia, but I am looking for more concrete examples and how they're used. For example primary keys in databases are (from what I've read) stored in BST structure or a variation of the BST (feel free to correct me on this) My question isn't limited Binary Search Trees (BSTs), it can include any variation such as red-black, AVL and so on.

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  • Building a balanced binary search tree

    - by Znarkus
    Hi! Is there a method to build a balanced binary search tree? Example: 1 2 3 4 5 6 7 8 9 5 / \ 3 etc / \ 2 4 / 1 I'm thinking there is a method to do this, without using the more complex self-balancing trees. Otherwise I can do it on my own, but someone probably have done this already :)

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  • How to prepare for a programming competition? Graphs, Stacks, Trees, oh my! [closed]

    - by Simucal
    Last semester I attended ACM's (Association for Computing Machinery) bi-annual programming competition at a local University. My University sent 2 teams of 3 people and we competed amongst other schools in the mid-west. We got our butts kicked. You are given a packet with about 11 problems (1 problem per page) and you have 4 hours to solve as many as you can. They'll run your program you submit against a set of data and your output must match theirs exactly. In fact, the judging is automated for the most part. In any case.. I went there fairly confident in my programming skills and I left there feeling drained and weak. It was a terribly humbling experience. In 4 hours my team of 3 people completed only one of the problems. The top team completed 4 of them and took 1st place. The problems they asked were like no problems I have ever had to answer before. I later learned that in order to solve them some of them effectively you have to use graphs/graph algorithms, trees, stacks. Some of them were simply "greedy" algo's. My question is, how can I better prepare for this semesters programming competition so I don't leave there feeling like a complete moron? What tips do you have for me to be able to answer these problems that involve graphs, trees, various "well known" algorithms? How can I easily identify the algorithm we should implement for a given problem? I have yet to take Algorithm Design in school so I just feel a little out of my element. Here are some examples of the questions asked at the competitions: ACM Problem Sets Update: Just wanted to update this since the latest competition is over. My team placed 1st for our small region (about 6-7 universities with between 1-5 teams each school) and ~15th for the midwest! So, it is a marked improvement over last years performance for sure. We also had no graduate students on our team and after reviewing the rules we found out that many teams had several! So, that would be a pretty big advantage in my own opinion. Problems this semester ranged from about 1-2 "easy" problems (ie bit manipulation, string manipulation) to hard (graph problems involving fairly complex math and network flow problems). We were able to solve 4 problems in our 5 hours. Just wanted to thank everyone for the resources they provided here, we used them for our weekly team practices and it definitely helped! Some quick tips that I have that aren't suggested below: When you are seated at your computer before the competition starts, quickly type out various data structures that you might need that you won't have access to in your languages libraries. I typed out a Graph data-structure complete with floyd-warshall and dijkstra's algorithm before the competition began. We ended up using it in our 2nd problem that we solved and this is the main reason why we solved this problem before anyone else in the midwest. We had it ready to go from the beginning. Similarly, type out the code to read in a file since this will be required for every problem. Save this answer "template" someplace so you can quickly copy/paste it to your IDE at the beginning of each problem. There are no rules on programming anything before the competition starts so get any boilerplate code out the way. We found it useful to have one person who is on permanent whiteboard duty. This is usually the person who is best at math and at working out solutions to get a head start on future problems you will be doing. One person is on permanent programming duty. Your fastest/most skilled "programmer" (most familiar with the language). This will save debugging time also. The last person has several roles between assessing the packet of problems for the next "easiest" problem, helping the person on the whiteboard work out solutions and helping the person programming work out bugs/issues. This person needs to be flexible and be able to switch between roles easily.

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  • Best Data Structure For Time Series Data

    - by TriParkinson
    Hi all, I wonder if someone could take a minute out of their day to give their two cents on my problem. I would like some suggestions on what would be the best data structure for representing, on disk, a large data set of time series data. The main priority is speed of insertion, with other priorities in decreasing order; speed of retrieval, size on disk, size in memory, speed of removal. I have seen that B+ trees are often used in database because of their fast search times, but how about for fast insertion times? Is a linked list really the way to go? Thanks in advance for your time, Tri

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  • UVa #112 Tree Summing

    - by unclerojelio
    I'm working on UVa #112 Tree Summing. I have what I think should be a working solution but it is not accepted by the online judge due to a basic misunderstanding of the problem on my part. Consider the following inputs: -1 (-1()()) 77 (77(1()())()) or diagrammatically, the trees look like: -1 77 / \ / \ () () 1 () / \ () () According to at least two working solutions, the correct output for the above inputs is: yes no However, I don't understand why the second one should be 'no'. It looks to me like the rightmost path of the tree should give the proper sum. What am I missing?

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  • Calculating depth and descendants of tree

    - by yuudachi
    Can you guys help me with the algorithm to do these things? I have preorder, inorder, and postorder implemented, and I am given the hint to traverse the tree with one of these orders. I am using dotty to label (or "visit") the nodes. Depth is the number of edges from the root to the bottom leaf, so everytime I move, I add +1 to the depth? Something like that? No idea about the algorithm for descendants. They are asking about the number of nodes a specific node has under itself. These are normal trees btw.

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  • Tree + Recursion..

    - by RBA
    Hi.. I came across an article on Binary Trees Search . It uses intensive Recursive Algorithms.. I am just so confused with these stuff.. Please guide my path so as I understand these problems at ease, or any good website to read about recursion first and then solving these problems.. Please share your experience on it.. Its very urgent, and I want to learn these concepts as soon as possible.. Thankss... Regards.

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  • How to create and Expression tree to do the same as "StartsWith"

    - by Jonathan
    Hi to all. Currently, I have this method to compare two numbers Private Function ETForGreaterThan(ByVal query As IQueryable(Of T), ByVal propertyValue As Object, ByVal propertyInfo As PropertyInfo) As IQueryable(Of T) Dim e As ParameterExpression = Expression.Parameter(GetType(T), "e") Dim m As MemberExpression = Expression.MakeMemberAccess(e, propertyInfo) Dim c As ConstantExpression = Expression.Constant(propertyValue, propertyValue.GetType()) Dim b As BinaryExpression = Expression.GreaterThan(m, c) Dim lambda As Expression(Of Func(Of T, Boolean)) = Expression.Lambda(Of Func(Of T, Boolean))(b, e) Return query.Where(lambda) End Function It works fine and is consumed in this way query = ETForGreaterThan(query, Value, propertyInfo) As you can see, I give it an IQueryable collection and it add a where clause to it, base on a property and a value. Y can construct Lessthan, LessOrEqualThan etc equivalents as Expression has this operators predefined. ¿How can I transform this code to do the same with strings? Expression don't give me a predefined operator like "contains" or "startwith" and I'm really noob with Expression trees. Thanks, and please Post your answer in C#/VB. Choose the one that make you feel more confortable.

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  • Ruby GraphViz Binary Tree Record

    - by Jason M
    I'm using the ruby-graphviz gem and I'm trying to draw binary trees. I'd like to use the record shape so that each node can have a left, middle, and right field and, thus, if there are two edges leaving a node, the left and right edges can be distinguished. I tried specifying the field by concatenating the field name like this: @node1.name + ":left" But that did not work. What is the correct way of specifying the field? require 'rubygems' require 'graphviz' @graph = GraphViz.new( :G, :type => :digraph ) @node1 = @graph.add_node("1", "shape" => "record", "label" => "<left>|<f1> 1|<right>" ) @node2 = @graph.add_node("2", "shape" => "record", "label" => "<left>|<f1> 2|<right>" ) @graph.add_edge(@node1.name + ":left", @node2) # generate a random filename filename = "/tmp/#{(0...8).map{65.+(rand(25)).chr}.join}.png" @graph.output( :png => filename ) exec "open #{filename}"

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  • Dynamic expression tree how to

    - by Savvas Sopiadis
    Hello everybody! Implemented a generic repository with several Methods. One of those is this: public IEnumerable<T> Find(Expression<Func<T, bool>> where) { return _objectSet.Where(where); } Given to be it is easy to call this like this: Expression<Func<Culture, bool>> whereClause = c => c.CultureId > 4 ; return cultureRepository.Find(whereClause).AsQueryable(); But now i see (realize) that this kind of quering is "limiting only to one criteria". What i would like to do is this: in the above example c is of type Culture. Culture has several properties like CultureId, Name, Displayname,... How would i express the following: CultureId 4 and Name.contains('de') and in another execution Name.contains('us') and Displayname.contains('ca') and .... Those queries should be created dynamically. I had a look in Expression trees (as i thought this to be a solution to my problem - btw i never used them before) but i cannot find anything which points to my requirement. How can this be costructed? Thanks in advance

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  • Algorithm to Render a Horizontal Binary-ish Tree in Text/ASCII form

    - by Justin L.
    It's a pretty normal binary tree, except for the fact that one of the nodes may be empty. I'd like to find a way to output it in a horizontal way (that is, the root node is on the left and expands to the right). I've had some experience expanding trees vertically (root node at the top, expanding downwards), but I'm not sure where to start, in this case. Preferably, it would follow these couple of rules: If a node has only one child, it can be skipped as redundant (an "end node", with no children, is always displayed) All nodes of the same depth must be aligned vertically; all nodes must be to the right of all less-deep nodes and to the left of all deeper nodes. Nodes have a string representation which includes their depth. Each "end node" has its own unique line; that is, the number of lines is the number of end nodes in the tree, and when an end node is on a line, there may be nothing else on that line after that end node. As a consequence of the last rule, the root node should be in either the top left or the bottom left corner; top left is preferred. For example, this is a valid tree, with six end nodes (node is represented by a name, and its depth): [a0]------------[b3]------[c5]------[d8] \ \ \----------[e9] \ \----[f5] \--[g1]--------[h4]------[i6] \ \--------------------[j10] \-[k3] Which represents the horizontal, explicit binary tree: 0 a / \ 1 g * / \ \ 2 * * * / \ \ 3 k * b / / \ 4 h * * / \ \ \ 5 * * f c / \ / \ 6 * i * * / / \ 7 * * * / / \ 8 * * d / / 9 * e / 10 j (branches folded for compactness; * representing redundant, one-child nodes; note that *'s are actual nodes, storing one child each, just with names omitted here for presentation sake) (also, to clarify, I'd like to generate the first, horizontal tree; not this vertical tree) I say language-agnostic because I'm just looking for an algorithm; I say ruby because I'm eventually going to have to implement it in ruby anyway. Assume that each Node data structure stores only its id, a left node, and a right node. A master Tree class keeps tracks of all nodes and has adequate algorithms to find: A node's nth ancestor A node's nth descendant The generation of a node The lowest common ancestor of two given nodes Anyone have any ideas of where I could start? Should I go for the recursive approach? Iterative?

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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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  • Find kth smallest element in a binary search tree in Optimum way

    - by Bragaadeesh
    Hi, I need to find the kth smallest element in the binary search tree without using any static/global variable. How to achieve it efficiently? The solution that I have in my mind is doing the operation in O(n), the worst case since I am planning to do an inorder traversal of the entire tree. But deep down I feel that I am not using the BST property here. Is my assumptive solution correct or is there a better one available ?

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  • binary search tree recursive subtree in java

    - by Art Peterson
    Can anyone point me to a code example (java preferably) or psuedocode that uses recursion to return a subtree that contains all nodes with keys between fromKey and toKey. So if I was to call Tree.subtree(5,10) it should return all nodes in the BST that have keys between 5 and 10 inclusive - but I can't use loops or helper methods...only recursive calls to the subtree method, which takes fromKey and toKey as parameters. Thanks!

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  • Pseudo LRU tree algorithm.

    - by patros
    A lot of descriptions of Pseudo LRU algorithms involve using a binary search tree, and setting flags to "point away" from the node you're searching for every time you access the tree. This leads to a reasonable approximation of LRU. However, it seems from the descriptions that all of the nodes deemed LRU would be leaf nodes. Is there a pseudo-LRU algorithm that deals with a static tree that will still perform reasonably well, while determining that non-leaf nodes are suitable LRU candidates?

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  • Parsing a given binary tree using python?

    - by kaushik
    Parse a binary tree,referring to given set of features,answering decision tree question at each node to decide left child or right child and find the path to leaf node according to answer given to the decision tree.. input wil be a set of feature which wil help in answering the question at each level to choose the left or right half and the output will be the leaf node.. i need help in implementing this can anyone suggest methods?? Please answer... thanks in advance..

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  • Building a directory tree from a list of file paths

    - by Abignale
    I am looking for a time efficient method to parse a list of files into a tree. There can be hundreds of millions of file paths. The brute force solution would be to split each path on occurrence of a directory separator, and traverse the tree adding in directory and file entries by doing string comparisons but this would be exceptionally slow. The input data is usually sorted alphabetically, so the list would be something like: C:\Users\Aaron\AppData\Amarok\Afile C:\Users\Aaron\AppData\Amarok\Afile2 C:\Users\Aaron\AppData\Amarok\Afile3 C:\Users\Aaron\AppData\Blender\alibrary.dll C:\Users\Aaron\AppData\Blender\and_so_on.txt From this ordering my natural reaction is to partition the directory listings into groups... somehow... before doing the slow string comparisons. I'm really not sure. I would appreciate any ideas. Edit: It would be better if this tree were lazy loaded from the top down if possible.

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  • Call asp.net mvc Html Helper within custom html helper with expression parameter

    - by Frank Michael Kraft
    I am trying to write an html helper extension within the asp.net mvc framework. public static MvcHtmlString PlatformNumericTextBoxFor<TModel>(this HtmlHelper instance, TModel model, Expression<Func<TModel,double>> selector) where TModel : TableServiceEntity { var viewModel = new PlatformNumericTextBox(); var func = selector.Compile(); MemberExpression memExpession = (MemberExpression)selector.Body; string name = memExpession.Member.Name; var message = instance.ValidationMessageFor<TModel, double>(selector); viewModel.name = name; viewModel.value = func(model); viewModel.validationMessage = String.Empty; var result = instance.Partial(typeof(PlatformNumericTextBox).Name, viewModel); return result; } The line var message = instance.ValidationMessageFor<TModel, double>(selector); has a syntax error. But I do not understand it. The error is: Fehler 2 "System.Web.Mvc.HtmlHelper" enthält keine Definition für "ValidationMessageFor", und die Überladung der optimalen Erweiterungsmethode "System.Web.Mvc.Html.ValidationExtensions.ValidationMessageFor(System.Web.Mvc.HtmlHelper, System.Linq.Expressions.Expression)" weist einige ungültige Argumente auf. C:\Projects\WorkstreamPlatform\WorkstreamPlatform_WebRole\Extensions\PlatformHtmlHelpersExtensions.cs 97 27 WorkstreamPlatform_WebRole So according to the message, the parameter is invalid. But the method is actually declared like this: public static MvcHtmlString ValidationMessageFor<TModel, TProperty>(this HtmlHelper<TModel> htmlHelper, Expression<Func<TModel, TProperty>> expression); So actually it should work.

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