abstract syntax tree - Page 10

Abstract Factory Pattern in C#

Liskov substitution principle with abstract parent class

Does Liskov substitution principle apply to inheritance hierarchies where the parent is an abstract class the same way if the parent is a concrete class? The Wikipedia page list several conditions that have to be met before a hierarchy is deemed to be correct. However, I have read in a blog post that one way to make things easier to conform to LSP is to use abstract parent instead of a concrete class. How does the choice of the parent type (abstract vs concrete) impacts the LSP? Is it better to have an abstract base class whenever possible?

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Enabling syntax highlighting for LESS in Programmer's Notepad?

- by Cody Gray

When I don't feel like firing up the Visual Studio behemoth, or when I don't have it installed, I always turn to Programmer's Notepad. It's an amazingly light and fast little text editor, with the special advantage that it is completely platform-native and conforms to standard UI conventions. Therefore, please do not suggest that I consider using other text editors. I've already considered and rejected them because they do not use native UI controls. I like Programmer's Notepad, thank you very much. Unfortunately, I've recently begun to learn, use, and love LESS for all of my CSS coding needs, and it appears that Programmer's Notepad is not bundled with a syntax highlighting scheme for LESS. Does anyone know if there is—by chance and good fortune—one already available somewhere on the web that some kind soul has tediously prepared? If not, how can I go about writing one of my own? Is there a way to build on the existing CSS scheme? It's also possible that any code coloring scheme designed for Scintilla-based editors will work, as Programmer's Notepad is based on the Scintilla control. If you know of a LESS highlighting scheme for Scintilla-based editors, and how to use that with Programmer's Notepad, please suggest that as well.

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adding nodes to a binary search tree randomly deletes nodes

- by SDLFunTimes

Hi, stack. I've got a binary tree of type TYPE (TYPE is a typedef of data*) that can add and remove elements. However for some reason certain values added will overwrite previous elements. Here's my code with examples of it inserting without overwriting elements and it not overwriting elements. the data I'm storing: struct data { int number; char *name; }; typedef struct data data; # ifndef TYPE # define TYPE data* # define TYPE_SIZE sizeof(data*) # endif The tree struct: struct Node { TYPE val; struct Node *left; struct Node *rght; }; struct BSTree { struct Node *root; int cnt; }; The comparator for the data. int compare(TYPE left, TYPE right) { int left_len; int right_len; int shortest_string; /* find longest string */ left_len = strlen(left->name); right_len = strlen(right->name); if(right_len < left_len) { shortest_string = right_len; } else { shortest_string = left_len; } /* compare strings */ if(strncmp(left->name, right->name, shortest_string) > 1) { return 1; } else if(strncmp(left->name, right->name, shortest_string) < 1) { return -1; } else { /* strings are equal */ if(left->number > right->number) { return 1; } else if(left->number < right->number) { return -1; } else { return 0; } } } And the add method struct Node* _addNode(struct Node* cur, TYPE val) { if(cur == NULL) { /* no root has been made */ cur = _createNode(val); return cur; } else { int cmp; cmp = compare(cur->val, val); if(cmp == -1) { /* go left */ if(cur->left == NULL) { printf("adding on left node val %d\n", cur->val->number); cur->left = _createNode(val); } else { return _addNode(cur->left, val); } } else if(cmp >= 0) { /* go right */ if(cur->rght == NULL) { printf("adding on right node val %d\n", cur->val->number); cur->rght = _createNode(val); } else { return _addNode(cur->rght, val); } } return cur; } } void addBSTree(struct BSTree *tree, TYPE val) { tree->root = _addNode(tree->root, val); tree->cnt++; } The function to print the tree: void printTree(struct Node *cur) { if (cur == 0) { printf("\n"); } else { printf("("); printTree(cur->left); printf(" %s, %d ", cur->val->name, cur->val->number); printTree(cur->rght); printf(")\n"); } } Here's an example of some data that will overwrite previous elements: struct BSTree myTree; struct data myData1, myData2, myData3; myData1.number = 5; myData1.name = "rooty"; myData2.number = 1; myData2.name = "lefty"; myData3.number = 10; myData3.name = "righty"; initBSTree(&myTree); addBSTree(&myTree, &myData1); addBSTree(&myTree, &myData2); addBSTree(&myTree, &myData3); printTree(myTree.root); Which will print: (( righty, 10 ) lefty, 1 ) Finally here's some test data that will go in the exact same spot as the previous data, but this time no data is overwritten: struct BSTree myTree; struct data myData1, myData2, myData3; myData1.number = 5; myData1.name = "i"; myData2.number = 5; myData2.name = "h"; myData3.number = 5; myData3.name = "j"; initBSTree(&myTree); addBSTree(&myTree, &myData1); addBSTree(&myTree, &myData2); addBSTree(&myTree, &myData3); printTree(myTree.root); Which prints: (( j, 5 ) i, 5 ( h, 5 ) ) Does anyone know what might be going wrong? Sorry if this post was kind of long.

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Tree Surgeon 2.0 - The future on the T4 Express

- by Malcolm Anderson

If you've never been a fan of TreeSurgeon (http://treesurgeon.codeplex.com/) then skip this post.However, if have been there have been some interesting developments over the last couple of years.The biggest one is T4Recently Bill Simser wrote a detailed post about the potential future of tree surgeon, called "Tree Surgeon - Alive and Kicking or Dead and Buried" He raised the question:Times have changed. Since that last release in 2008 so much has changed for .NET developers. The question is, today is the project still viable? Do we still need a tool to generate a project tree given that we have things like scaffolding systems, NuGet, and T4 templates. Or should we just give the project its rightful and respectful send off as its had a good life and has outlived its usefulness.For myself, the answer is, keep it.I've spent the last couple of years doing agile engineering coaching and architecture and from my experience, I can tell you, there are a lot of shops out there that would benefit from having Tree Surgeon as a viable product. Many would benefit simply from having the software engineering information that is embedded in the tree surgeon site be floating around their conversation.Little things like, keep all of your software needed to run the build, with the build in the version control system.Have your developers and the build system using the same build.Have a one-touch buildSeparate your code from your interfacePut unit tests in first, not lastI've seen companies with great developers suffer from the problems that naturally come from builds taking 3 and 4 hours to run. It takes work to get that build down to 10 minutes, but the benefits are always worth it. Tree Surgeon gives you a leg up, by starting you off with a project that you can drop into your Continuous Integration system, right out of the box.Well, it used to be right out of the box. Today, you have to play with the project to make it work for you, but even with the issues (it hasn't been updated since 2008) it still gives you a framework, with logical separations that you can build from.If you have used Tree Surgeon in the past, take a few minutes and drop a comment about what difference it made in your development style, and what you are doing differently today because of it.

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Why does PHP 5.2 disallow abstract static class methods?

- by Artem Russakovskii

After enabling strict warnings in PHP 5.2, I saw a load of strict standards warnings from a project that was originally written without strict warnings: Strict Standards: Static function Program::getSelectSQL() should not be abstract in Program.class.inc The function in question belongs to an abstract parent class Program and is declared abstract static because it should be implemented in its child classes, such as TVProgram. I did find references to this change here: Dropped abstract static class functions. Due to an oversight, PHP 5.0.x and 5.1.x allowed abstract static functions in classes. As of PHP 5.2.x, only interfaces can have them. My question is: can someone explain in a clear way why there shouldn't be an abstract static function in PHP?

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RIF PRD: Presentation syntax issues

- by Charles Young

Over Christmas I got to play a bit with the W3C RIF PRD and came across a few issues which I thought I would record for posterity. Specifically, I was working on a grammar for the presentation syntax using a GLR grammar parser tool (I was using the current CTP of ‘M’ (MGrammer) and Intellipad – I do so hope the MS guys don’t kill off M and Intellipad now they have dropped the other parts of SQL Server Modelling). I realise that the presentation syntax is non-normative and that any issues with it do not therefore compromise the standard. However, presentation syntax is useful in its own right, and it would be great to iron out any issues in a future revision of the standard. The main issues are actually not to do with the grammar at all, but rather with the ‘running example’ in the RIF PRD recommendation. I started with the code provided in Example 9.1. There are several discrepancies when compared with the EBNF rules documented in the standard. Broadly the problems can be categorised as follows: · Parenthesis mismatch – the wrong number of parentheses are used in various places. For example, in GoldRule, the RHS of the rule (the ‘Then’) is nested in the LHS (‘the If’). In NewCustomerAndWidgetRule, the RHS is orphaned from the LHS. Together with additional incorrect parenthesis, this leads to orphanage of UnknownStatusRule from the entire Document. · Invalid use of parenthesis in ‘Forall’ constructs. Parenthesis should not be used to enclose formulae. Removal of the invalid parenthesis gave me a feeling of inconsistency when comparing formulae in Forall to formulae in If. The use of parenthesis is not actually inconsistent in these two context, but in an If construct it ‘feels’ as if you are enclosing formulae in parenthesis in a LISP-like fashion. In reality, the parenthesis is simply being used to group subordinate syntax elements. The fact that an If construct can contain only a single formula as an immediate child adds to this feeling of inconsistency. · Invalid representation of compact URIs (CURIEs) in the context of Frame productions. In several places the URIs are not qualified with a namespace prefix (‘ex1:’). This conflicts with the definition of CURIEs in the RIF Datatypes and Built-Ins 1.0 document. Here are the productions: CURIE ::= PNAME_LN | PNAME_NS PNAME_LN ::= PNAME_NS PN_LOCAL PNAME_NS ::= PN_PREFIX? ':' PN_LOCAL ::= ( PN_CHARS_U | [0-9] ) ((PN_CHARS|'.')* PN_CHARS)? PN_CHARS ::= PN_CHARS_U | '-' | [0-9] | #x00B7 | [#x0300-#x036F] | [#x203F-#x2040] PN_CHARS_U ::= PN_CHARS_BASE | '_' PN_CHARS_BASE ::= [A-Z] | [a-z] | [#x00C0-#x00D6] | [#x00D8-#x00F6] | [#x00F8-#x02FF] | [#x0370-#x037D] | [#x037F-#x1FFF] | [#x200C-#x200D] | [#x2070-#x218F] | [#x2C00-#x2FEF] | [#x3001-#xD7FF] | [#xF900-#xFDCF] | [#xFDF0-#xFFFD] | [#x10000-#xEFFFF] PN_PREFIX ::= PN_CHARS_BASE ((PN_CHARS|'.')* PN_CHARS)? The more I look at CURIEs, the more my head hurts! The RIF specification allows prefixes and colons without local names, which surprised me. However, the CURIE Syntax 1.0 working group note specifically states that this form is supported…and then promptly provides a syntactic definition that seems to preclude it! However, on (much) deeper inspection, it appears that ‘ex1:’ (for example) is allowed, but would really represent a ‘fragment’ of the ‘reference’, rather than a prefix! Ouch! This is so completely ambiguous that it surely calls into question the whole CURIE specification. In any case, RIF does not allow local names without a prefix. · Missing ‘External’ specifiers for built-in functions and predicates. The EBNF specification enforces this for terms within frames, but does not appear to enforce (what I believe is) the correct use of External on built-in predicates. In any case, the running example only specifies ‘External’ once on the predicate in UnknownStatusRule. External() is required in several other places. · The List used on the LHS of UnknownStatusRule is comma-delimited. This is not supported by the EBNF definition. Similarly, the argument list of pred:list-contains is illegally comma-delimited. · Unnecessary use of conjunction around a single formula in DiscountRule. This is strictly legal in the EBNF, but redundant. All the above issues concern the presentation syntax used in the running example. There are a few minor issues with the grammar itself. Note that Michael Kiefer stated in his paper “Rule Interchange Format: The Framework” that: “The presentation syntax of RIF … is an abstract syntax and, as such, it omits certain details that might be important for unambiguous parsing.” · The grammar cannot differentiate unambiguously between strategies and priorities on groups. A processor is forced to resolve this by detecting the use of IRIs and integers. This could easily be fixed in the grammar. · The grammar cannot unambiguously parse the ‘->’ operator in frames. Specifically, ‘-’ characters are allowed in PN_LOCAL names and hence a parser cannot determine if ‘status->’ is (‘status’ ‘->’) or (‘status-’ ‘>’). One way to fix this is to amend the PN_LOCAL production as follows: PN_LOCAL ::= ( PN_CHARS_U | [0-9] ) ((PN_CHARS|'.')* ((PN_CHARS)-('-')))? However, unilaterally changing the definition of this production, which is defined in the SPARQL Query Language for RDF specification, makes me uncomfortable. · I assume that the presentation syntax is case-sensitive. I couldn’t find this stated anywhere in the documentation, but function/predicate names do appear to be documented as being case-sensitive. · The EBNF does not specify whitespace handling. A couple of productions (RULE and ACTION_BLOCK) are crafted to enforce the use of whitespace. This is not necessary. It seems inconsistent with the rest of the specification and can cause parsing issues. In addition, the Const production exhibits whitespaces issues. The intention may have been to disallow the use of whitespace around ‘^^’, but any direct implementation of the EBNF will probably allow whitespace between ‘^^’ and the SYMSPACE. Of course, I am being a little nit-picking about all this. On the whole, the EBNF translated very smoothly and directly to ‘M’ (MGrammar) and proved to be fairly complete. I have encountered far worse issues when translating other EBNF specifications into usable grammars. I can’t imagine there would be any difficulty in implementing the same grammar in Antlr, COCO/R, gppg, XText, Bison, etc. A general observation, which repeats a point made above, is that the use of parenthesis in the presentation syntax can feel inconsistent and un-intuitive. It isn’t actually inconsistent, but I think the presentation syntax could be improved by adopting braces, rather than parenthesis, to delimit subordinate syntax elements in a similar way to so many programming languages. The familiarity of braces would communicate the structure of the syntax more clearly to people like me. If braces were adopted, parentheses could be retained around ‘var (frame | ‘new()’) constructs in action blocks. This use of parenthesis feels very LISP-like, and I think that this is my issue. It’s as if the presentation syntax represents the deformed love-child of LISP and C. In some places (specifically, action blocks), parenthesis is used in a LISP-like fashion. In other places it is used like braces in C. I find this quite confusing. Here is a corrected version of the running example (Example 9.1) in compliant presentation syntax: Document( Prefix( ex1 <http://example.com/2009/prd2> ) (* ex1:CheckoutRuleset *) Group rif:forwardChaining ( (* ex1:GoldRule *) Group 10 ( Forall ?customer such that And(?customer # ex1:Customer ?customer[ex1:status->"Silver"]) (Forall ?shoppingCart such that ?customer[ex1:shoppingCart->?shoppingCart] (If Exists ?value (And(?shoppingCart[ex1:value->?value] External(pred:numeric-greater-than-or-equal(?value 2000)))) Then Do(Modify(?customer[ex1:status->"Gold"]))))) (* ex1:DiscountRule *) Group ( Forall ?customer such that ?customer # ex1:Customer (If Or( ?customer[ex1:status->"Silver"] ?customer[ex1:status->"Gold"]) Then Do ((?s ?customer[ex1:shoppingCart-> ?s]) (?v ?s[ex1:value->?v]) Modify(?s [ex1:value->External(func:numeric-multiply (?v 0.95))])))) (* ex1:NewCustomerAndWidgetRule *) Group ( Forall ?customer such that And(?customer # ex1:Customer ?customer[ex1:status->"New"] ) (If Exists ?shoppingCart ?item (And(?customer[ex1:shoppingCart->?shoppingCart] ?shoppingCart[ex1:containsItem->?item] ?item # ex1:Widget ) ) Then Do( (?s ?customer[ex1:shoppingCart->?s]) (?val ?s[ex1:value->?val]) (?voucher ?customer[ex1:voucher->?voucher]) Retract(?customer[ex1:voucher->?voucher]) Retract(?voucher) Modify(?s[ex1:value->External(func:numeric-multiply(?val 0.90))])))) (* ex1:UnknownStatusRule *) Group ( Forall ?customer such that ?customer # ex1:Customer (If Not(Exists ?status (And(?customer[ex1:status->?status] External(pred:list-contains(List("New" "Bronze" "Silver" "Gold") ?status)) ))) Then Do( Execute(act:print(External(func:concat("New customer: " ?customer)))) Assert(?customer[ex1:status->"New"])))) ) ) I hope that helps someone out there :-)

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protected abstract override Foo(); – er... what?

- by Muljadi Budiman

A couple of weeks back, a co-worker was pondering a situation he was facing. He was looking at the following class hierarchy: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { } class FirstConcrete : SecondaryBase { } class SecondConcrete : SecondaryBase { } Basically, the first 2 classes are abstract classes, but the OriginalBase class has Test implemented as a virtual method. What he needed was to force concrete class implementations to provide a proper body for the Test method, but he can’t do mark the method as abstract since it is already implemented in the OriginalBase class. One way to solve this is to hide the original implementation and then force further derived classes to properly implemented another method that will replace it. The code will look like the following: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { protected sealed override void Test() { Test2(); } protected abstract void Test2(); } class FirstConcrete : SecondaryBase { // Have to override Test2 here } class SecondConcrete : SecondaryBase { // Have to override Test2 here } With the above code, SecondaryBase class will seal the Test method so it can no longer be overridden. Then it also made an abstract method Test2 available, which will force the concrete classes to override and provide the proper implementation. Calling Test will properly call the proper Test2 implementation in each respective concrete classes. I was wondering if there’s a way to tell the compiler to treat the Test method in SecondaryBase as abstract, and apparently you can, by combining the abstract and override keywords. The code looks like the following: abstract class OriginalBase { protected virtual void Test() { } } abstract class SecondaryBase : OriginalBase { protected abstract override void Test(); } class FirstConcrete : SecondaryBase { // Have to override Test here } class SecondConcrete : SecondaryBase { // Have to override Test here } The method signature makes it look a bit funky, because most people will treat the override keyword to mean you then need to provide the implementation as well, but the effect is exactly as we desired. The concepts are still valid: you’re overriding the Test method from its original implementation in the OriginalBase class, but you don’t want to implement it, rather you want to classes that derive from SecondaryBase to provide the proper implementation, so you also make it as an abstract method. I don’t think I’ve ever seen this before in the wild, so it was pretty neat to find that the compiler does support this case.

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APress Deal of the Day 4/June/2014 - C# Quick Syntax Reference

- by TATWORTH

Originally posted on: http://geekswithblogs.net/TATWORTH/archive/2014/06/04/apress-deal-of-the-day-4june2014---c-quick-syntax.aspxToday’s $10 Deal of the Day from APress at http://www.apress.com/9781430262800 is C# Quick Syntax Reference. “The C# Quick Syntax Reference is a condensed code and syntax reference to the C# programming language. It presents the essential C# syntax in a well-organized format that can be used as a handy reference.”

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Worst Case number of rotations for BST to AVL algorithm?

- by spacker_lechuck

I have a basic algorithm below and I know that the worst case input BST is one that has degenerated to a linked list from inserts to only one side. How would I compute the worst case complexity in terms of number of rotations for this BST to AVL conversion algorithm? IF tree is right heavy { IF tree's right subtree is left heavy { Perform Double Left rotation } ELSE { Perform Single Left rotation } } ELSE IF tree is left heavy { IF tree's left subtree is right heavy { Perform Double Right rotation } ELSE { Perform Single Right rotation } }

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Modifying a gedit syntax highlighting file

- by Oscar Saleta Reig

I am trying to change a highlighting file from Gedit. I have modified the file /usr/share/gtksourceview-3.0/language-specs/fortran.lang because I want to change the cases in which the editor takes a statement as a comment. The problem I have is that when I choose the new highlighting scheme nothing highlights, it just remains as plain text. The file fortran.lang was opened with su permissions and I just copy-pasted everything into a new Gedit file and later saved it as fortran_enhanced.lang in the same folder. The changes I've done to the original file are these: Original fortran.lang file: <language id="fortran" _name="Fortran 95" version="2.0" _section="Sources"> <metadata> <property name="mimetypes">text/x-fortran</property> <property name="globs">*.f;*.f90;*.f95;*.for</property> <property name="line-comment-start">!</property> </metadata> <styles> <style id="comment" _name="Comment" map-to="def:comment"/> <style id="floating-point" _name="Floating Point" map-to="def:floating-point"/> <style id="keyword" _name="Keyword" map-to="def:keyword"/> <style id="intrinsic" _name="Intrinsic function" map-to="def:builtin"/> <style id="boz-literal" _name="BOZ Literal" map-to="def:base-n-integer"/> <style id="decimal" _name="Decimal" map-to="def:decimal"/> <style id="type" _name="Data Type" map-to="def:type"/> </styles> <default-regex-options case-sensitive="false"/> <definitions>  <context id="line-comment" style-ref="comment" end-at-line-end="true" class="comment" class-disabled="no-spell-check"> <start>!|(^[Cc](\b|[^OoAaYy]))</start> <include> <context ref="def:escape"/> <context ref="def:in-line-comment"/> </include> </context> (...) Modified fortran_enhanced.lang file:  <language id="fortran_enhanced" _name="Fortran 95 2.0" version="2.0" _section="Sources"> <metadata> <property name="mimetypes">text/x-fortran</property>  <property name="globs">*.f90;*.f95;</property> <property name="line-comment-start">!</property> </metadata> <styles> <style id="comment" _name="Comment" map-to="def:comment"/> <style id="floating-point" _name="Floating Point" map-to="def:floating-point"/> <style id="keyword" _name="Keyword" map-to="def:keyword"/> <style id="intrinsic" _name="Intrinsic function" map-to="def:builtin"/> <style id="boz-literal" _name="BOZ Literal" map-to="def:base-n-integer"/> <style id="decimal" _name="Decimal" map-to="def:decimal"/> <style id="type" _name="Data Type" map-to="def:type"/> </styles> <default-regex-options case-sensitive="false"/> <definitions>  <context id="line-comment" style-ref="comment" end-at-line-end="true" class="comment" class-disabled="no-spell-check"> <start>!</start> <include> <context ref="def:escape"/> <context ref="def:in-line-comment"/> </include> </context> (...) I have read this question [ Custom gedit Syntax Highlighting for Dummies? ] and I tried to make the new fortran_enhanced.lang file readable with $ cd /usr/share/gtksourceview-3.0/language-specs $ sudo chmod 0644 fortran_enhanced.lang but it doesn't seem that made some difference. I have to say that I have never done a thing like this before and I don't even understand most of the language file, so I am open to every criticism, as I have been guided purely by intuition. Thank you in advanced!

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GWT: Change padding of tree rows?

- by Epaga

A GWT tree looks roughly like this: <div class="gwt-Tree"> <div style="padding-top: 3px; padding-right: 3px; padding-bottom: 3px; margin-left: 0px; padding-left: 23px;"> <div style="display:inline;" class="gwt-TreeItem"> <table> ... </table> </div> </div> <div ...> </div> ... </div> My question is: how should I change the padding of the individual tree rows? I suppose I could do something along the lines of setting CSS rules for .gwt-Tree > div but that seems hacky. Is there a more elegant way?

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red black tree balancing?

- by Anirudh Kaki

i am working to generate tango tree, where i need to check whether every sub tree in tango is balanced or not. if its not balanced i need to make it balance? I trying so hard to make entire RB-tree balance but i not getting any proper logic so can any one help me out?? here i am adding code to check how to find my tree is balanced are not but when its not balanced how can i make it balance. static boolean verifyProperty5(rbnode n) { int left = 0, right = 0; if (n != null) { bh++; left = blackHeight(n.left, 0); right = blackHeight(n.right, 0); } if (left == right) { System.out.println("black height is :: " + bh); return true; } else { System.out.println("in balance"); return false; } } public static int blackHeight(rbnode root, int len) { bh = 0; blackHeight(root, path1, len); return bh; } private static void blackHeight(rbnode root, int path1[], int len) { if (root == null) return; if (root.color == "black"){ root.black_count = root.parent.black_count+1; } else{ root.black_count = root.parent.black_count; } if ((root.left == null) && (root.right == null)) { bh = root.black_count; } blackHeight(root.left, path1, len); blackHeight(root.right, path1, len); }

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C++ find largest BST in a binary tree

- by fonjibe

what is your approach to have the largest BST in a binary tree? I refer to this post where a very good implementation for finding if a tree is BST or not is bool isBinarySearchTree(BinaryTree * n, int min=std::numeric_limits<int>::min(), int max=std::numeric_limits<int>::max()) { return !n || (min < n->value && n->value < max && isBinarySearchTree(n->l, min, n->value) && isBinarySearchTree(n->r, n->value, max)); } It is quite easy to implement a solution to find whether a tree contains a binary search tree. i think that the following method makes it: bool includeSomeBST(BinaryTree* n) { if(!isBinarySearchTree(n)) { if(!isBinarySearchTree(n->left)) return isBinarySearchTree(n->right); } else return true; else return true; } but what if i want the largest BST? this is my first idea, BinaryTree largestBST(BinaryTree* n) { if(isBinarySearchTree(n)) return n; if(!isBinarySearchTree(n->left)) { if(!isBinarySearchTree(n->right)) if(includeSomeBST(n->right)) return largestBST(n->right); else if(includeSomeBST(n->left)) return largestBST(n->left); else return NULL; else return n->right; } else return n->left; } but its not telling the largest actually. i struggle to make the comparison. how should it take place? thanks

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Why can't RB-Tree be a list?

- by Alex

Hey everyone. I have a problem with the rb-trees. according to wikipedia, rb-tree needs to follow the following: A node is either red or black. The root is black. (This rule is used in some definitions and not others. Since the root can always be changed from red to black but not necessarily vice-versa this rule has little effect on analysis.) All leaves are black. Both children of every red node are black. Every simple path from a given node to any of its descendant leaves contains the same number of black nodes. As we know, an rb-tree needs to be balanced and has the height of O(log(n)). But, if we insert an increasing series of numbers (1,2,3,4,5...) and theoretically we will get a tree that will look like a list and will have the height of O(n) with all its nodes black, which doesn't contradict the rb-tree properties mentioned above. So, where am I wrong?? thanks.

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navigate all items in a wpf tree view

- by Brian Leahy

I want to be able to traverse the visual ui tree looking for an element with an ID bound to the visual element's Tag property. I'm wondering how i do this. Controls don't have children to traverse. I started using LogicalTreeHelper.GetChildren, which seems to work as intended, up until i hit a TreeView control... then LogicalTreeHelper.GetChildren doesnt return any children. Note: the purpose is to find the visual UI element that corresponds to the data item. That is, given an ID of the item, Go find the UI element displaying it. Edit: I am apparently am not explaining this well enough. I am binding some data objects to a TreeView control and then wanting to select a specific item programaticly given that business object's ID. I dont see why it's so hard to travers the visual tree and find the element i want, as the data object's ID is in the Tag property of the appropriate visual element. I'm using Mole and I am able to find the UI element with the appropriate ID in it's Tag. I just cannot find the visual element in code. LogicalTreeHelper does not traverse any items in the tree. Neither does ItemContainerGenerator.ContainerFromItem retrieve anything for items in the tree view.

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Evaluate an expression tree

- by Phronima

Hi, This project that I'm working on requires that an expression tree be constructed from a string of single digit operands and operators both represented as type char. I did the implmentation and the program up to that point works fine. I'm able to print out the inorder, preorder and postorder traversals in the correct way. The last part calls for evaulating the expression tree. The parameters are an expression tree "t" and its root "root". The expression tree is ((3+2)+(6+2)) which is equal to 13. Instead I get 11 as the answer. Clearly I'm missing something here and I've done everything short of bashing my head against the desk. I would greatly appreciate it if someone can point me in the right direction. (Note that at this point I'm only testing addition and will add in the other operators when I get this method working.) public int evalExpression( LinkedBinaryTree t, BTNode root ) { if( t.isInternal( root ) ) { int x = 0, y = 0, value = 0; char operator = root.element(); if( root.getLeft() != null ) x = evalExpression(t, t.left( root ) ); if( root.getRight() != null ) y = evalExpression(t, t.right( root ) ); if( operator == '+' ) { value = value + Character.getNumericValue(x) + Character.getNumericValue(y); } return value; } else { return root.element(); } }

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Flex Tree Properties, Null Reference?

- by mvrak

I am pulling down a large XML file and I have no control over it's structure. I used a custom function to use the tag name to view the tree structure as a flex tree, but then it breaks. I am guessing it has something to do with my other function, one that calls attribute values from the selected node. See code. <mx:Tree x="254" y="21" width="498" height="579" id="xmllisttree" labelFunction="namer" dataProvider="{treeData}" showRoot="false" change="treeChanged(event)" /> //and the Cdata import mx.rpc.events.ResultEvent; [Bindable] private var fullXML:XMLList; private function contentHandler(evt:ResultEvent):void{ fullXML = evt.result.page; } [Bindable] public var selectedNode:Object; public function treeChanged(event:Event):void { selectedNode=Tree(event.target).selectedItem; } public function namer(item:Object):String { var node:XML = XML(item); var nodeName:QName = node.name(); var stringtest:String ="bunny"; return nodeName.localName; } The error is TypeError: Error #1009: Cannot access a property or method of a null object reference. Where is the null reference?

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R Tree 50,000 foot overview?

- by roufamatic

I'm working on a school project that involves taking a lat/long point and finding the top five closest points in a known list of places. The list is to be stored in memory, with the caveat that we must choose an "appropriate data structure" -- that is, we cannot simply store all the places in an array and compare distances one-by-one in a linear fashion. The teacher suggested grouping the place data by US State to prevent calculating the distance for places that are obviously too far away. I think I can do better. From my research online it seems like an R-Tree or one of its variants might be a neat solution. Unfortunately, that sentence is as far as I've gotten with understanding the actual technique, as the literature is simply too dense for my non-academic head. Can somebody give me a really high overview of what the process is for populating an R-Tree with lat/long data, and then traversing the tree to find those 5 nearest neighbors of a given point? Additionally the project is in C, and I don't have to reinvent the wheel on this, so if you've used an existing open source C implementation of an R Tree I'd be interested in your experiences.

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Sorting by some field and fetching whole tree from DB

- by Niaxon

Hello everyone, I am trying to do file browser in a tree form and have a problem to sort it somehow. I use PHP and MySQL for that. I've created mixed (nested set + adjacency) table 'element' with the following fields: element_id, left_key, right_key, level, parent_id, element_name, element_type (enum: 'folder','file'), element_size. Let's not discuss right now that it is better to move information about element (name, type, size) into other table. Function to scan specified directory and fill table work correctly. Noteworthy, i am adding elements to tree in specific order: folders first and only files. After that i can easily fetch and display whole table on the page using simple query: SELECT * FROM element WHERE 1=1 ORDER BY left_key With the result of that query and another function i can generate correct html code (<ul><li>... and so on). Now back to the question (finally, huh?). I am struggling to add sorting functionality. For example i want to order my result by size. Here i need to keep in my mind whole hierarchy of tree and rule: folders first, files later. I believe i can do that by generating in PHP recursive query: SELECT * FROM element WHERE parent_id = {$parentId} ORDER BY element_type (so folders would be first), size (or name for example) After that for each result which is folder i will send another query to get it's content. Also it's possible to fetch whole tree by left_key and after that sort it in PHP as array but i guess that would be worse :) I wonder if there is better and more efficient way to do such thing?

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python recursive iteration exceeding limit for tree implementation

- by user3698027

I'm implementing a tree dynamically in python. I have defined a class like this... class nodeobject(): def __init__(self,presentnode=None,parent=None): self.currentNode = presentnode self.parentNode = parent self.childs = [] I have a function which gets possible childs for every node from a pool def findchildren(node, childs): # No need to write the whole function on how it gets childs Now I have a recursive function that starts with the head node (no parent) and moves down the chain recursively for every node (base case being the last node having no children) def tree(dad,children): for child in children: childobject = nodeobject(child,dad) dad.childs.append(childobject) newchilds = findchildren(child, children) if len(newchilds) == 0: lastchild = nodeobject(newchilds,childobject) childobject.childs.append(lastchild) loopchild = copy.deepcopy(lastchild) while loopchild.parentNode != None: print "last child" else: tree(childobject,newchilds) The tree formation works for certain number of inputs only. Once the pool gets bigger, it results into "MAXIMUM RECURSION DEPTH EXCEEDED" I have tried setting the recursion limit with set.recursionlimit() and it doesn't work. THe program crashes. I want to implement a stack for recursion, can someone please help, I have gone no where even after trying for a long time ?? Also, is there any other way to fix this other than stack ?

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Simulation tree command in C

- by Ecle

I have to create the simulation of tree command in C, this is my current code: #include <stdio.h> #include <sys/types.h> #include <sys/stat.h> #include <dirent.h> #include <string.h> main(int argc, char *argv[]){ int i; if(argc < 2){ printf("\nError. Use: %s directory\n", argv[0]); system("exit"); } for(i=1;i<argc;i++) //if(argv[i][0] != '-') tree(argv[i]); } tree(char *ruta){ DIR *dirp; struct dirent *dp; static nivel = 0; struct stat buf; char fichero[256]; int i; if((dirp = opendir(path)) == NULL){ perror(path); return; } while((dp = readdir(dirp)) != NULL){ printf(fichero, "%s/%s", path, dp->d_name); if((buf.st_mode & S_IFMT) == S_IFDIR){ for(i=0;i<nivel;i++) printf("\t"); printf("%s\n", dp->d_name); ++nivel; tree(fichero); --nivel; } } } Apparently, it works! (due to it compiles correctly) But I don't why. I can't pass the correct arguments to execute this. Thank you so much, people.

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Dynamic Tree control in Flex 3

- by nimmyliji

I am looking for sample code to create a dynamic Tree control in Flex using a Collection of objects obtained from the backend(Perl cgi). So, initially the Tree will display the root nodes. Clicking root node, will invoke the data for populating the child nodes (basically adding child nodes on demand). Clicking child nodes will pull another collection add child nodes of child node. So, lets assume Initially the Tree will display - Root1 Root2 Root3 Clicking Root1 will display something like this - Root1 Child 1 Child 2 Root2 Root3 And Clicking Child1 will display - Root1 Child 1 Child1 of Child 1 Child2 of Child 1 Child 2 Root2 Root3 Is it possible? Thanks in advance...

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Metalanguage like BNF or XML-Schema to validate a tree-instance against a tree-model

- by Stefan

Hi! I'm implementing a new machine learning algorithm in Java that extracts a prototype datastructure from a set of structured datasets (tree-structure). As im developing a generic library for that purpose, i kept my design independent from concrete data-representations like XML. My problem now is that I need a way to define a data model, which is basically a ruleset describing valid trees, against which a set of trees is being matched. I thought of using BNF or a similar dialect. Basically I need a way to iterate through the space of all valid TreeNodes defined by the ModelTree (Like a search through the search space for algorithms like A*) so that i can compare my set of concrete trees with the model. I know that I'll have to deal with infinite spaces there but first things first. I know, it's rather tricky (and my sentences are pretty bumpy) but I would appreciate any clues. Thanks in advance, Stefan

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how to handle duplicates in AVL tree

- by Ahmed Kotb

I want to make my avl tree support adding duplicates but there is a problem with the default behavior of the binary search tree with duplicates that the rotation could make nodes with equal key be on the left and the right of the parent for example adding A,A,A will cause the tree to do a rotation to be something like that A / \ A A so getting all the entries with that key will be a problem...and searching in both direction is not something good the solution that i have thought of is making each node stores an array of duplicates so when adding a new item that already exists will be just adding a new item to the array , removing item with key will delete the whole node while the find all items with key will return that array. are there are any other methods to handle duplicates ?

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