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• C# - Determine if class initializaion causes infinite recursion?

  - by John M

  I am working on porting a VB6 application to C# (Winforms 3.5) and while doing so I'm trying to break up the functionality into various classes (ie database class, data validation class, string manipulation class). Right now when I attempt to run the program in Debug mode the program pauses and then crashes with a StackOverFlowException. VS 2008 suggests a infinite recursion cause. I have been trying to trace what might be causing this recursion and right now my only hypothesis is that class initializations (which I do in the header(?) of each class). My thought is this: mainForm initializes classA classA initializes classB classB initializes classA .... Does this make sense or should I be looking elsewhere? UPDATE1 (a code sample): mainForm namespace john { public partial class frmLogin : Form { stringCustom sc = new sc(); stringCustom namespace john { class stringCustom { retrieveValues rv = new retrieveValues(); retrieveValues namespace john { class retrieveValues { stringCustom sc = new stringCustom();

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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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• What does this recursive function do?

  - by null

  What does this function do? And how do you evaluate it? How to trace it? How to understand recursive method? I just can't understand the recursion, and the exam date is coming soon, and I know in order to understand recursion, I must first understand recursion. But I just can't write a slightly complex recursive method, can anyone help me out using the simplest English words. public class BalancedStrings { public static void printBalanced(String prefix, int a, int b) { if (a > 0) printBalanced(prefix + "a", a - 1, b); if (b > 0) printBalanced(prefix + "b", a, b - 1); if (a == 0 && b == 0) System.out.println(prefix); } public static void printBalanced(int n) { if (n % 2 == 0) { printBalanced("", n / 2, n / 2); } } public static void main(String[] args) { printBalanced(4); } }

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• Recursive solution to finding patterns

  - by user2997162

  I was solving a problem on recursion which is to count the total number of consecutive 8's in a number. For example: input: 8801 output: 2 input: 801 output: 0 input: 888 output: 3 input: 88088018 output:4 I am unable to figure out the logic of passing the information to the next recursive call about whether the previous digit was an 8. I do not want the code but I need help with the logic. For an iterative solution, I could have used a flag variable, but in recursion how do I do the work which flag variable does in an iterative solution. Also, it is not a part of any assignment. This just came to my mind because I am trying to practice coding using recursion.

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• Class Decorators, Inheritence, super(), and maximum recursion

  - by jamstooks

  I'm trying to figure out how to use decorators on subclasses that use super(). Since my class decorator creates another subclass a decorated class seems to prevent the use of super() when it changes the className passed to super(className, self). Below is an example: def class_decorator(cls): class _DecoratedClass(cls): def __init__(self): return super(_DecoratedClass, self).__init__() return _DecoratedClass class BaseClass(object): def __init__(self): print "class: %s" % self.__class__.__name__ def print_class(self): print "class: %s" % self.__class__.__name__ bc = BaseClass().print_class() class SubClass(BaseClass): def print_class(self): super(SubClass, self).print_class() sc = SubClass().print_class() @class_decorator class SubClassAgain(BaseClass): def print_class(self): super(SubClassAgain, self).print_class() sca = SubClassAgain() # sca.print_class() # Uncomment for maximum recursion The output should be: class: BaseClass class: BaseClass class: SubClass class: SubClass class: _DecoratedClass Traceback (most recent call last): File "class_decorator_super.py", line 34, in <module> sca.print_class() File "class_decorator_super.py", line 31, in print_class super(SubClassAgain, self).print_class() ... ... RuntimeError: maximum recursion depth exceeded while calling a Python object Does anyone know of a way to not break a subclass that uses super() when using a decorator? Ideally I'd like to reuse a class from time to time and simply decorate it w/out breaking it.

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• Help me understand Inorder Traversal without using recursion

  - by vito

  I am able to understand preorder traversal without using recursion, but I'm having a hard time with inorder traversal. I just don't seem to get it, perhaps, because I haven't understood the inner working of recursion. This is what I've tried so far: def traverseInorder(node): lifo = Lifo() lifo.push(node) while True: if node is None: break if node.left is not None: lifo.push(node.left) node = node.left continue prev = node while True: if node is None: break print node.value prev = node node = lifo.pop() node = prev if node.right is not None: lifo.push(node.right) node = node.right else: break The inner while-loop just doesn't feel right. Also, some of the elements are getting printed twice; may be I can solve this by checking if that node has been printed before, but that requires another variable, which, again, doesn't feel right. Where am I going wrong? I haven't tried postorder traversal, but I guess it's similar and I will face the same conceptual blockage there, too. Thanks for your time! P.S.: Definitions of Lifo and Node: class Node: def __init__(self, value, left=None, right=None): self.value = value self.left = left self.right = right class Lifo: def __init__(self): self.lifo = () def push(self, data): self.lifo = (data, self.lifo) def pop(self): if len(self.lifo) == 0: return None ret, self.lifo = self.lifo return ret

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• Why am I unable to turn off recursion in ISC BIND?

  - by nbolton

  Here's my named.conf.options file: options { directory "/var/cache/bind"; dnssec-enable yes; auth-nxdomain no; # conform to RFC1035 listen-on-v6 { any; }; # disable recursion recursion no; }; I've tried adding allow-recursion { "none"; } before recursion but this also has no effect; I'm testing it by using nslookup on Windows, and using google.com. as the query (and it returns an IP, so I assume recursion is on). This issue occurs on two servers with similar setups.

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• Pascals Triangle by recursion

  - by Olpers

  Note : My Class Teacher gave me this question as an assignment... I am not asked to do it but please tell me how to do it with recursion Binomial coefficients can be calculated using Pascal's triangle: 1 n = 0 1 1 1 2 1 1 3 3 1 1 4 6 4 1 n = 4 Each new level of the triangle has 1's on the ends; the interior numbers are the sums of the two numbers above them. Task: Write a program that includes a recursive function to produce a list of binomial coefficients for the power n using the Pascal's triangle technique. For example, Input = 2 Output = 1 2 1 Input = 4 Output = 1 4 6 4 1 done this So Far but tell me how to do this with recursion... #include<stdio.h> int main() { int length,i,j,k; //Accepting length from user printf("Enter the length of pascal's triangle : "); scanf("%d",&length); //Printing the pascal's triangle for(i=1;i<=length;i++) { for(j=1;j<=length-i;j++) printf(" "); for(k=1;k<i;k++) printf("%d",k); for(k=i;k>=1;k--) printf("%d",k); printf("\n"); } return 0; }

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• List all files and dirs without recursion with junctions

  - by naxa

  Is there a native|portable tool that can give me an unicode (or at least system local-compatible) list of all files and directories under a path recursively, without recursing into junction points or links, in Windows? For example, the built-in dir command, as well as takeown and icacls run into an infinite loop with the Application Data directory (1). EDIT I would like to be able to get a text file or at least easy clipboard transfer as output.

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• Php recursion into multidimensional array

  - by dclowd9901

  I'm trying to write a script that, in its process, would need to be able to write an undefined number of nested arrays, and those arrays need to be able to have custom keys. Essentially, the script is being used to convert an HTML DOM into a multidimensional array. I'm not extremely well versed in recursion, so any pointers would be awesome.

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• Python class decorator and maximum recursion depth exceeded

  - by Michal Lula

  I try define class decorator. I have problem with __init__ method in decorated class. If __init__ method invokes super the RuntimeError maximum recursion depth exceeded is raised. Code example: def decorate(cls): class NewClass(cls): pass return NewClass @decorate class Foo(object): def __init__(self, *args, **kwargs): super(Foo, self).__init__(*args, **kwargs) What I doing wrong? Thanks, Michal

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• Removing left recursion

  - by equilibrium

  The following grammar has left recursion E= E+T|T T= T*F|F F= a|b|c How to remove it? Is there any general procedure for it?

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• sequence with and without recursion

  - by Sergey

  I have a sequence. a1 = 1 - cos(x); ai = a1 + (-1)^(i-1) * x^(2*i-2) / (2*i-2)! I need to write this with and without recursion. But it has a different results. Here is my code: http://codepaste.net/q213q6

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• multiplying big numbers using recursion and array

  - by persian Dev

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

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• What are the pros and cons of using manual list iteration vs recursion through fail

  - by magus

  I come up against this all the time, and I'm never sure which way to attack it. Below are two methods for processing some season facts. What I'm trying to work out is whether to use method 1 or 2, and what are the pros and cons of each, especially large amounts of facts. methodone seems wasteful since the facts are available, why bother building a list of them (especially a large list). This must have memory implications too if the list is large enough ? And it doesn't take advantage of Prolog's natural backtracking feature. methodtwo takes advantage of backtracking to do the recursion for me, and I would guess would be much more memory efficient, but is it good programming practice generally to do this? It's arguably uglier to follow, and might there be any other side effects? One problem I can see is that each time fail is called, we lose the ability to pass anything back to the calling predicate, eg. if it was methodtwo(SeasonResults), since we continually fail the predicate on purpose. So methodtwo would need to assert facts to store state. Presumably(?) method 2 would be faster as it has no (large) list processing to do? I could imagine that if I had a list, then methodone would be the way to go.. or is that always true? Might it make sense in any conditions to assert the list to facts using methodone then process them using method two? Complete madness? But then again, I read that asserting facts is a very 'expensive' business, so list handling might be the way to go, even for large lists? Any thoughts? Or is it sometimes better to use one and not the other, depending on (what) situation? eg. for memory optimisation, use method 2, including asserting facts and, for speed use method 1? season(spring). season(summer). season(autumn). season(winter). % Season handling showseason(Season) :- atom_length(Season, LenSeason), write('Season Length is '), write(LenSeason), nl. % ------------------------------------------------------------- % Method 1 - Findall facts/iterate through the list and process each %-------------------------------------------------------------- % Iterate manually through a season list lenseason([]). lenseason([Season|MoreSeasons]) :- showseason(Season), lenseason(MoreSeasons). % Findall to build a list then iterate until all done methodone :- findall(Season, season(Season), AllSeasons), lenseason(AllSeasons), write('Done'). % ------------------------------------------------------------- % Method 2 - Use fail to force recursion %-------------------------------------------------------------- methodtwo :- % Get one season and show it season(Season), showseason(Season), % Force prolog to backtrack to find another season fail. % No more seasons, we have finished methodtwo :- write('Done').

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• Recursion problem in algorithm

  - by Marthin

  I'm not sure if this is the right place to post this, but the problem actually belongs to a programming assignment. Solve the recursion: T(0) = 2; T(n) = T(n-1) + 2; Solution: T(n) = 2(n+1) Could someone please show me how they got to that solution?

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• Why infinite recursion leads to seg fault

  - by Pqr

  Why infinite recursion leads to seg fault ? Why stack overflow leads to seg fault. I am looking for detailed explanation. int f() { f(); } int main() { f(); }

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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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• Tail recursion in Erlang

  - by dagda1

  Hi, I am really struggling to understand tail recursion in Erlang. I have the following eunit test: db_write_many_test() -> Db = db:new(), Db1 = db:write(francesco, london, Db), Db2 = db:write(lelle, stockholm, Db1), ?assertEqual([{lelle, stockholm},{francesco, london}], Db2). And here is my implementation: -module(db) . -include_lib("eunit/include/eunit.hrl"). -export([new/0,write/3]). new() -> []. write(Key, Value, Database) -> Record = {Key, Value}, [Record|append(Database)]. append([H|T]) -> [H|append(T)]; append([]) -> []. Is my implementation tail recursive and if not, how can I make it so? Thanks in advance

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• Recursion in Unity and Dispose pattern implementation

  - by Budda

  My class is inherited from UnityContainer (from Unity 2.0), here is source code: public class UnityManager : UnityContainer { private UnityManager() { _context = new MyDataClassesDataContext(); // ... } protected override void Dispose(bool disposing) { if ( disposing ) { _context.Dispose(); } base.Dispose(disposing); } private readonly CMCoreDataClassesDataContext _context; } When Dispose method is called for the instance of UnityManager class it drop into recursion... Why? As far as I know base.Dispose should call the Dispose method of base class only... isn't it? Who call back the Dispose(bool) of UnityManager? How to prevent that? Thanks.

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• Detecting Infinite recursion in Python or dynamic languages

  - by drozzy

  Recently I tried compiling program something like this with GCC: int f(int i){ if(i<0){ return 0;} return f(i-1); and it ran just fine. When I inspected the stack frames the compiler optimized the program to use only one frame, by just jumping back to the beginning of the function and only replacing the arguments to f. And - the compiler wasn't even running in optimized mode. Now, when I try the same thing in Python - I hit maximum recursion wall (or stack overflow). Is there way that a dynamic language like python can take advantage of these nice optimizations? Maybe it's possible to use a compiler instead of an interpreter to make this work? Just curious!

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• javascript too much recursion?

  - by Ken

  Hi, I'm trying to make a script that automatically starts uploading after the data has been enter in the database(I need the autoId that the database makes to upload the file). When I run the javascript the scripts runs the php file but it fails calling the other php to upload the file. too much recursion setTimeout(testIfToegevoegd(),500); the script that gives the error send("/projects/backend/nieuwDeeltaak.php",'deeltaakNaam='+f.deeltaaknaam.value+'&beschrijving='+ f.beschrijving.value+'&startDatum='+f.startDatum.value+'&eindDatum='+f.eindDatum.value +'&deeltaakLeider='+f.leiderID.value+'&projectID='+f.projectID.value,id); function testIfToegevoegd(){ if(document.getElementById('resultaat').innerHTML == "<b>De deeltaak werd toegevoegd</b>"){ //stop met testen + upload file document.getElementById('nieuwDeeltaak').target = 'upload_target'; document.forms["nieuwDeeltaak"].submit() }else{ setTimeout(testIfToegevoegd(),500); } } testIfToegevoegd(); sorry for the dutch names we have to use them it is a school project. when I click the button that calls all this for a second time (after the error) it works fine.

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• PHP object parent/child recursion

  - by Damien

  I've got a parent-child OO relationship. Parent obejcts has many child objects and every child object knows about it's parent by reference. The parent can be a child too (basically its a tree). When i do a var_dump() on the root object it says ["parent"]=RECURSION many times and the generated description will be really long. I'm wondering if i do something wrong. If yes, i'm interested in the "best practice". Thanks for the help!

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• .NET Performance: Deep Recursion vs Queue

  - by JeffN825

  I'm writing a component that needs to walk large object graphs, sometimes 20-30 levels deep. What is the most performant way of walking the graph? A. Enqueueing "steps" so as to avoid deep recursion or B. A DFS (depth first search) which may step many levels deep and have a "deep" stack trace at times. I guess the question I'm asking is: Is there a performance hit in .NET for doing a DFS that causes a "deep" stack trace? If so, what is the hit? And would I better better off with some BFS by means of queueing up steps that would have been handled recursively in a DFS? Sorry if I'm being unclear. Thanks.

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• Infinite recursion trying to check all elements of a TreeCtrl

  - by mavnn

  I have a TreeCtrl in which more than one Item can be assigned the same object as PyData. When the object is updated, I want to update all of the items in the tree which have that object as their PyData. I thought the following code would solve the problem quite neatly, but for some reason the logical test (current != self.GetFirstVisibleItem()) always returns true leading to infinite recursion. Can anyone explain why? def RefreshNodes(self, obj, current=None): print "Entered refresh" current = current or self.GetFirstVisibleItem() if current.IsOk(): print self.GetPyData(current).name if self.GetPyData(current) == obj: self.RefreshNode(current) current = self.GetNextVisible(current) if current != self.GetFirstVisibleItem(): self.RefreshNodes(obj, current) Edit: the above is obviously part of a class based on wx.TreeCtrl

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