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  • F#: Recursive collect and filter over N-ary Tree

    - by RodYan
    This is hurting my brain! I want to recurse over a tree structure and collect all instances that match some filter into one list. Here's a sample tree structure type Tree = | Node of int * Tree list Here's a test sample tree: let test = Node((1, [Node(2, [Node(3,[]); Node(3,[])]); Node(3,[])])) Collecting and filtering over nodes with and int value of 3 should give you output like this: [Node(3,[]);Node(3,[]);Node(3,[])]

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  • I need an abstract field !

    - by Jules Olléon
    I know abstract fields do not exist in java. I also read this question but the solutions proposed won't solve my problem. Maybe there is no solution, but it's worth asking :) Problem I have an abstract class that does an operation in the constructor depending on the value of one of its fields. The problem is that the value of this field will change depending on the subclass. How can I do so that the operation is done on the value of the field redefined by the subclass ? If I just "override" the field in the subclass the operation is done on the value of the field in the abstract class. I'm open to any solution that would ensure that the operation will be done during the instantiation of the subclass (ie putting the operation in a method called by each subclass in the constructor is not a valid solution, because someone might extend the abstract class and forget to call the method). Also, I don't want to give the value of the field as an argument of the constructor. Is there any solution to do that, or should I just change my design ?

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  • In-order tree traversal

    - by Chris S
    I have the following text from an academic course I took a while ago about in-order traversal (they also call it pancaking) of a binary tree (not BST): In-order tree traversal Draw a line around the outside of the tree. Start to the left of the root, and go around the outside of the tree, to end up to the right of the root. Stay as close to the tree as possible, but do not cross the tree. (Think of the tree — its branches and nodes — as a solid barrier.) The order of the nodes is the order in which this line passes underneath them. If you are unsure as to when you go “underneath” a node, remember that a node “to the left” always comes first. Here's the example used (slightly different tree from below) However when I do a search on google, I get a conflicting definition. For example the wikipedia example: Inorder traversal sequence: A, B, C, D, E, F, G, H, I (leftchild,rootnode,right node) But according to (my understanding of) definition #1, this should be A, B, D, C, E, F, G, I, H Can anyone clarify which definition is correct? They might be both describing different traversal methods, but happen to be using the same name. I'm having trouble believing the peer-reviewed academic text is wrong, but can't be certain.

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  • Syntax highlight in java for android

    - by Mohit Deshpande
    I want to build an notepad-style application on android that will have syntax highlighting. But when I search around the web, I find the syntax highlighting can be done only through use of an awt class. How could I syntax highlight in maybe a custom EditText or TextView view? I know that the release of a syntax highlighter is sort of anticipated, so I want to add my syntax highlighter on the market.

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  • MySQL Syntax error when trying to reset Joomla password

    - by Arthur
    I'm trying to reset my Joomla admin password by executing the following code in MySQL: INSERT INTO `jos_users` (`id`,`name`, `username`, `password`, `params`) VALUES (LAST_INSERT_ID(),'Administrator2', 'admin2', 'd2064d358136996bd22421584a7cb33e:trd7TvKHx6dMeoMmBVxYmg0vuXEA4199', ''); INSERT INTO `jos_user_usergroup_map` (`user_id`,`group_id`) VALUES (LAST_INSERT_ID(),'8'); When I attempt to execute it, I get the following error: Failed to execute SQL : SQL INSERT INTO `jos_users` (`id`,`name`, `username`, `password`, `params`) VALUES (LAST_INSERT_ID(),'Administrator2', 'admin2', 'd2064d358136996bd22421584a7cb33e:trd7TvKHx6dMeoMmBVxYmg0vuXEA4199', ''); INSERT INTO `jos_user_usergroup_map` (`user_id`,`group_id`) VALUES (LAST_INSERT_ID(),'8'); failed : You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INSERT INTO `jos_user_usergroup_map` (`user_id`,`group_id`) VALUES (LAST_INSERT_' at line 1 Could someone tell me where my Syntax might be wrong? I'm using MySQL version 5.0.95.

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  • Scene graphs and spatial partitioning structures: What do you really need?

    - by tapirath
    I've been fiddling with 2D games for awhile and I'm trying to go into 3D game development. I thought I should get my basics right first. From what I read scene graphs hold your game objects/entities and their relation to each other like 'a tire' would be the child of 'a vehicle'. It's mainly used for frustum/occlusion culling and minimizing the collision checks between the objects. Spatial partitioning structures on the other hand are used to divide a big game object (like the map) to smaller parts so that you can gain performance by only drawing the relevant polygons and again minimizing the collision checks to those polygons only. Also a spatial partitioning data structure can be used as a node in a scene graph. But... I've been reading about both subjects and I've seen a lot of "scene graphs are useless" and "BSP performance gain is irrelevant with modern hardware" kind of articles. Also some of the game engines I've checked like gameplay3d and jmonkeyengine are only using a scene graph (That also may be because they don't want to limit the developers). Whereas games like Quake and Half-Life only use spatial partitioning. I'm aware that the usage of these structures very much depend on the type of the game you're developing so for the sake of clarity let's assume the game is a FPS like Counter-Strike with some better outdoor environment capabilities (like a terrain). The obvious question is which one is needed and why (considering the modern hardware capabilities). Thank you.

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  • On Windows 7, dir or tree can't show unicode characters, even starting cmd with cmd /U

    - by Jian Lin
    On Windows 7, dir or tree can't show unicode characters, even starting cmd with cmd /U So I would press Window Key + R to run something, and type in cmd /U so that the content might handle Unicode. And then using dir or tree /F, the content in Unicode won't show as Unicode. (in Window Explorer (file manager), the Unicode will show) Is there a way to handle it? To get Unicode characters to test your filenames, you can go to http://news.google.com/news?edchanged=1&ned=tw and you will be able to get many Unicode characters there (UTF-8)

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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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  • recursion tree and binary tree cost calculation

    - by Tony
    Hi all, I've got the following recursion: T(n) = T(n/3) + T(2n/3) + O(n) The height of the tree would be log3/2 of 2. Now the recursion tree for this recurrence is not a complete binary tree. It has missing nodes lower down. This makes sense to me, however I don't understand how the following small omega notation relates to the cost of all leaves in the tree. "... the total cost of all leaves would then be Theta (n^log3/2 of 2) which, since log3/2 of 2 is a constant strictly greater then 1, is small omega(n lg n)." Can someone please help me understand how the Theta(n^log3/2 of 2) becomes small omega(n lg n)?

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  • SQL server - climb up in the tree structure

    - by Vytas999
    Hello. I have some sql table, named Object, which saves tree data in fields ObjectID, ParentID, and others. I have implemented recurse procedure, which select everything down by objectID from tree, like this: 1. 1.1. 1.2. 1.2.1. ... Now o need to "Climb up" - by some ObjectID i need to select everything Up, like this: 1.2.1. 1.2. 1. How i can do that? In example, my "down" procedure looks like: ALTER PROCEDURE [dbo].[Object_SelectDownByRoot_Simple] @ObjectID int AS WITH tree (ObjectID, ParentID, ObjectName, ObjectCode) AS ( SELECT ObjectID, ParentID, ObjectName, ObjectCode FROM dbo.[ObjectQ] ofs WHERE( ObjectID = @ObjectID ) UNION ALL SELECT ofs.ObjectID, ofs.ParentID, ofs.ObjectName, ofs.ObjectCode FROM dbo.[ObjectQ] ofs JOIN tree ON tree.ObjectID = ofs.ParentID ) SELECT ObjectID, ParentID, ObjectName, ObjectCode FROM tree

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  • how do i supply data to my gwt tree

    - by molleman
    Hello, So i need to create a tree with tree items for my gwt project. i am using the composite pattern to store all the information i need to be placed within a tree. A User has a root Folder that extends Hierarchy, this root Folder then has a list of Hierarchy objects, that can be FileLocations or Folders. Trouble i am having is building my tree based on this pattern. this data is all stored using hibernate in a mysql database How would i be able to implement this as a tree in gwt. Also the tree item that i create would have to reference back to the object so i can rename or move it.

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  • On Windows 7, dir or tree can't show unicode characters, even starting cmd with cmd /U

    - by ????
    On Windows 7, dir or tree can't show unicode characters, even starting cmd with cmd /U So I would press Window Key + R to run something, and type in cmd /U so that the content might handle Unicode. And then using dir or tree /F, the content in Unicode won't show as Unicode. (in Window Explorer (file manager), the Unicode will show) Is there a way to handle it? To get Unicode characters to test your filenames, you can go to http://news.google.com/news?edchanged=1&ned=tw and you will be able to get many Unicode characters there (UTF-8)

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  • Pure functional bottom up tree algorithm

    - by Axel Gneiting
    Say I wanted to write an algorithm working on an immutable tree data structure that has a list of leaves as its input. It needs to return a new tree with changes made to the old tree going upwards from those leaves. My problem is that there seems to be no way to do this purely functional without reconstructing the entire tree checking at leaves if they are in the list, because you always need to return a complete new tree as the result of an operation and you can't mutate the existing tree. Is this a basic problem in functional programming that only can be avoided by using a better suited algorithm or am I missing something?

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  • Correcting tree from messed up file tree in NTFS partition

    - by Fullmooninu
    It's a real messed situation, but I'm quite at the end of my options. It's my personal hardrive, so it's very important for me, and yes, I have no backup =( The short story: 1) I have two discs. One with Windows, and another where I had a bit of empty space at the front of the disk, so i could install Linux. The rest was occupied by a 1.8TB NTFS partition filled with data. 2) I installed Linux, and after a while realized there was not enough space for everything, so I tried using Gparted, and told it to re-size the NTFS partition, to a lesser size. 3) The system jammed. I had to reboot and broke the Resizing operation. Here's what I did to fix it: a) Rebooted into Linux Live, and used Testdisk,to deep analyze the disk, and recover the possible partitions. It found several versions of the NTFS partitions, probably made during the resizing. I told Testdisk to open every one of them, and only one could list its files. When trying to open the other options on Testdisk, it showed an error message. I assumed the one without errors, to be the correct one, and I told Testdisk to recover the partition, and write a new MBR. b) The partition had errors, and Linux has a NTFS fixing tool, used it, but the system still had errors. c) So I booted into windows and use chkdsk to correct all errors in the partition. d) Everything seems fine, but now, back in Windows, when I open one file, it opens another file, or part of another file. As in, some files took up the position of other files. What I think happened is that I recovered an old tree, and not the most current one. And that one just happened to be intact, while the most recent one was damaged. As such, the files that were moved during the failed resizing, were now, during the automatic correction, assumed wrongly to be in their correct places. So when I open a file, it tries to open another one. Radiohead - Creep.mp3 will open and it will actually be a bit from another song, or even code from a jpg. Some files seem to be all right, but others have seemed to have had their position taken by others. Anyone knows of something really powerful that can help me solve this?

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  • Array "tree" creation from db table

    - by Tural Teyyuboglu
    Trying to create array tree for db driven navigation. Getting following errur: array_key_exists() expects exactly 2 parameters, 1 given on line if (!array_key_exists($tree[$parent]['children'][$id])) Function looks like that $tree = array(); $sql = "SELECT id, parent, name FROM menu WHERE parent ... etc.... "; $results = mysql_query($sql) or die(mysql_error()); while(list($id, $parent, $name) = mysql_fetch_assoc($results)) { $tree[$id] = array('name' => $name, 'children' => array(), 'parent' => $parent); if (!array_key_exists($tree[$parent]['children'][$id])) { $tree[$parent]['children'][$id] = $id; } } Db structure How can I fix that? Whats wrong in this function?

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  • 'abstract class' versus 'normal class' for a reusable library

    - by Greg
    I'm developing a reusable library and have been creating abstract classes, so the client can then extend from these. QUESTION: Is there any reason in fact I should use an abstract class here as opposed to just a normal class? Note - Have already decided I do not want to use interfaces as I want to include actual default methods in my library so the client using it doesn't have to write the code.

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  • Django: Inherit Permssions from abstract models?

    - by lazerscience
    Is it possible to inherit permissions from an abstract model in Django? I can not really find anything about that. For me this doesn't work! class PublishBase(models.Model): class Meta: abstract = True get_latest_by = 'created' permissions = (('change_foreign_items', "Can change other user's items"),) EDIT: Not working means it fails silently. Permission is not created, as it wouldn't exist on the models inheriting from this class.

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  • C#: Abstract classes need to implement interfaces?

    - by bguiz
    My test code in C#: namespace DSnA { public abstract class Test : IComparable { } } Results in the following compiler error: error CS0535: 'DSnA.Test' does not implement interface member 'System.IComparable.CompareTo(object)' Since the class Test is an abstract class, why does the compiler require it to implement the interface? Shouldn't this requirement only be compulsory for concrete classes?

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  • What is the purpose of abstract classes?

    - by SpikETidE
    I am trying to learn OOP in PHP, and I have some confusion about interfaces and abstract classes. They both contain no implementations, only definitions, and should be implemented through their sub-classes. What part of abstract classes clearly distinguishes them from interfaces? Also, due to their apparent similarities, based on what reasons should I decide to use one over the other?

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  • Abstract attributes in Python

    - by deamon
    What is the shortest / most elegant way to implement the following Scala code with an abstract attribute in Python? abstract class Controller { val path: String } A subclass of Controller is enforced to define "path" by the Scala compiler. A subclass would look like this: class MyController extends Controller { override val path = "/home" }

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  • Object of an abstract class

    - by webgenius
    Why is it not possible to create an object of an abstract class? I understand that the compiler creates a VTABLE with VPTR pointing to NULL. Does this prevent from creating an object of an abstract class?

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  • Difference between abstract class and interface

    - by nectar
    A class implementing an interface has to implement all the methods of the interface, but if that class is implementing an abctract class is it necessary to implement all abstract methods? If not, can we create the object of that class which is implementing the Abstract class???

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  • Deriving a class from an abstract class (C++)

    - by cemregoksu
    I have an abstract class with a pure virtual function f() and i want to create a class inherited from that class, and also override function f(). I seperated the header file and the cpp file. I declared the function f(int) in the header file and the definition is in the cpp file. However, the compiler says the derived class is still abstract. How can i fix it?

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