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• What was your the most impressive technical programming achievement performed to impress a romantic

  - by DVK

  OK, so the archetypal human story is for a guy to go out and impress the girl with some wonderful achievement like slaying a dragon or building a monument or conquering neighboring tribe. This being enlightened 21st century on SO, let's morph this into a: StackOverflower performing a feat of programming to impress a romantic interest. There are two ways to do this: Technical achievement: Impressing a person with suitable background/understanding of programming with actual coding powerss you displayed. A dumb movie example would be that kid in "Hackers" move showing off his hacking skills in front of Angeline Jolie. Artistic achievement: Impressing a person with a result of running said code, whether they understand just how incredible the code itself is. An example is the animated ANSI rose (for a guy who actually wrote the ANSI code) This question is only about the first kind (technical achievements) - e.g. the person of interest was presented with impressive code/design that (s)he was able to properly appreciate. Rules (what doesn't qualify): The target audience must have been a person of romantic interest (prospective or present significant other or random hook-up). E.g. showing your program to your sister who's also a software developer doesn't count. The achievement must have been done specifically with the goal to impress such a person. However, it is OK if the achievement was done to impress a generic qualifying person, not someone specific. Although... if you write code to impress girls in general, I'd say "get a better idea of the opposite sex" The achievement must have been done with the goal of impressing the person. In other words, if you would have done it without romantic interest's knowledge anyway, it doesn't count. As examples, the following does not count: programming for your job. Programming for a coding contest. Open Source program that you'd have done anyway. The precise nature of the awesomeness of the achievement is somewhat irrelevant - from learning entire J2EE in 2 days to writing fancy game engine to implementing Python compiler in LOGO. As long as it's programming/software development related. The achievement should preferably be something other people would rank highly as well. If your date was impressed with your skill at calculating Fibonacci sequence without recursive function calls, it doesn't mean most developers will be. But it does mean you need to start finding better things to do on dates ;)

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• Monotouch - ICSharpCode.SharpZipLib giving an error

  - by Claudio

  Hy guys, I'm trying to generate a Zip File with ICSharpCode.SharpZipLib library but it's throwing a really weird error. Code: public static void ZipFiles(string inputFolderPath, string outputPathAndFile, string password) { ArrayList ar = GenerateFileList(inputFolderPath); // generate file list int TrimLength = (Directory.GetParent(inputFolderPath)).ToString().Length; TrimLength += 1; //remove '\' FileStream ostream; byte[] obuffer; ZipOutputStream oZipStream = new ZipOutputStream(File.Create(outputPathAndFile)); // create zip stream if (password != null && password != String.Empty) oZipStream.Password = password; oZipStream.SetLevel(9); // maximum compression ZipEntry oZipEntry; foreach (string Fil in ar) // for each file, generate a zipentry { oZipEntry = new ZipEntry(Fil.Remove(0, TrimLength)); oZipStream.PutNextEntry(oZipEntry); if (!Fil.EndsWith(@"/")) // if a file ends with '/' its a directory { ostream = File.OpenRead(Fil); obuffer = new byte[ostream.Length]; ostream.Read(obuffer, 0, obuffer.Length); oZipStream.Write(obuffer, 0, obuffer.Length); } } oZipStream.Finish(); oZipStream.Close(); } private static ArrayList GenerateFileList(string Dir) { ArrayList fils = new ArrayList(); bool Empty = true; foreach (string file in Directory.GetFiles(Dir,"*.xml")) // add each file in directory { fils.Add(file); Empty = false; } if (Empty) { if (Directory.GetDirectories(Dir).Length == 0) // if directory is completely empty, add it { fils.Add(Dir + @"/"); } } foreach (string dirs in Directory.GetDirectories(Dir)) // recursive { foreach (object obj in GenerateFileList(dirs)) { fils.Add(obj); } } return fils; // return file list } Error: Unhandled Exception: System.NotSupportedException: CodePage 437 not supported at System.Text.Encoding.GetEncoding (Int32 codepage) [0x00000] in <filename unknown>:0 at ICSharpCode.SharpZipLib.Zip.ZipConstants.ConvertToArray (System.String str) [0x00000] in <filename unknown>:0 at ICSharpCode.SharpZipLib.Zip.ZipConstants.ConvertToArray (Int32 flags, System.String str) [0x00000] in <filename unknown>:0 at ICSharpCode.SharpZipLib.Zip.ZipOutputStream.PutNextEntry (ICSharpCode.SharpZipLib.Zip.ZipEntry entry) [0x00000] in <filename unknown>:0 at WpfPrototype1.MainInvoicesView.ZipFiles (System.String inputFolderPath, System.String outputPathAndFile, System.String password) [0x00000] in <filename unknown>:0 at WpfPrototype1.MainInvoicesView.<ViewDidLoad>m__6 (System.Object , System.EventArgs ) [0x00000] in <filename unknown>:0 at MonoTouch.UIKit.UIControlEventProxy.Activated () [0x00000] in <filename unknown>:0 at (wrapper managed-to-native) MonoTouch.UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr) at MonoTouch.UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00000] in <filename unknown>:0 at MonoTouch.UIKit.UIApplication.Main (System.String[] args) [0x00000] in <filename unknown>:0 at WpfPrototype1.Application.Main (System.String[] args) [0x00000] in <filename unknown>:0 How can I make this code support CodePage 437? Regards, Claudio

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• Silverlight 4 DataBinding: Binding to ObservableCollection<string> not working anymore

  - by Kurt

  Upgrading from SL3 - SL4. First problem: this throws a parser exception: <StackPanel Name={Binding} /> (same with x:Name) Collection is ObservableCollection<string>. Worked fine in SL3. So it seems that SL4 doen't allow binding to the Name property. Huh? So: changed to <StackPanel Tag={Binding} /> ... since I just need to ID the control in code behind. So here's the bug ('cuz this has got to be a bug!): In this frag, AllAvailableItems is an ObservableCollection<string>: <ItemsControl Name="lbItems" ItemsSource="{Binding AllAvailableItems}" Height="Auto" Width="Auto" BorderBrush="Transparent" BorderThickness="0" VerticalAlignment="Top" HorizontalAlignment="Left" Margin="12,6,0,0"> <ItemsControl.ItemTemplate> <DataTemplate> <Grid> <Grid.RowDefinitions> <RowDefinition /> <RowDefinition /> </Grid.RowDefinitions> <CheckBox Tag="{Binding}" Checked="ItemChecked_Click" Unchecked="ItemUnchecked_Click" Style="{StaticResource CheckBoxStyle}" Grid.Row="0"> <CheckBox.Content> <TextBlock Text="{Binding}" Style="{StaticResource FormLJustStyle}" /> </CheckBox.Content> </CheckBox> <StackPanel Tag="{Binding}" Orientation="Vertical" Grid.Row="1"> <configControls:ucLanguage /> <!-- simple user control --> </StackPanel> </Grid> </DataTemplate> </ItemsControl.ItemTemplate> </ItemsControl> In the code behind, I use a recursive function to find the Dependency object with either the Name or Tag property provided: public static T FindVisualChildByName<T>(DependencyObject parent, string name, DependencyProperty propToUse) where T : DependencyObject { for (int i = 0; i < VisualTreeHelper.GetChildrenCount(parent); i++) { var child = VisualTreeHelper.GetChild(parent, i); string controlName = child.GetValue(propToUse) as string; if (controlName == name) { return child as T; } else { T result = FindVisualChildByName<T>(child, name, propToUse); if (result != null) return result; } } return null; } OK, get this: in the code behind, I can get the control that is ORDERED FIRST in the XAML! In other words, if I put the CheckBox first, I can retrieve the CheckBox, but no StackPanel. And vice-versa. This all worked fine in SL3. Any help, ideas ... ? Thanks - Kurt

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• hand coding a parser

  - by John Leidegren

  For all you compiler gurus, I wanna write a recursive descent parser and I wanna do it with just code. No generating lexers and parsers from some other grammar and don't tell me to read the dragon book, i'll come around to that eventually. I wanna get into the gritty details about implementing a lexer and parser for a reasonable simple langauge, say CSS. And I wanna do this right. This will probably end up being a series of questions but right now I'm starting with a lexer. Tokenization rules for CSS can be found here. I find my self writing code like this (hopefully you can infer the rest from this snippet): public CssToken ReadNext() { int val; while ((val = _reader.Read()) != -1) { var c = (char)val; switch (_stack.Top) { case ParserState.Init: if (c == ' ') { continue; // ignore } else if (c == '.') { _stack.Transition(ParserState.SubIdent, ParserState.Init); } break; case ParserState.SubIdent: if (c == '-') { _token.Append(c); } _stack.Transition(ParserState.SubNMBegin); break; What is this called? and how far off am I from something reasonable well understood? I'm trying to balence something which is fair in terms of efficiency and easy to work with, using a stack to implement some kind of state machine is working quite well, but I'm unsure how to continue like this. What I have is an input stream, from which I can read 1 character at a time. I don't do any look a head right now, I just read the character then depending on the current state try to do something with that. I'd really like to get into the mind set of writing reusable snippets of code. This Transition method is currently means to do that, it will pop the current state of the stack and then push the arguments in reverse order. That way, when I write Transition(ParserState.SubIdent, ParserState.Init) it will "call" a sub routine SubIdent which will, when complete, return to the Init state. The parser will be implemented in much the same way, currently, having everyhing in a single big method like this allows me to easily return a token when I found one, but it also forces me to keep everything in one single big method. Is there a nice way to split these tokenization rules into seperate methods? Any input/advice on the matter would be greatly appriciated!

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• How to dynamically expand a string in C

  - by sa125

  Hi - I have a function that recursively makes some calculations on a set of numbers. I want to also pretty-print the calculation in each recursion call by passing the string from the previous calculation and concatenating it with the current operation. A sample output might look like this: 3 (3) + 2 ((3) + 2) / 4 (((3) + 2) / 4) x 5 ((((3) + 2) / 4) x 5) + 14 ... and so on So basically, the second call gets 3 and appends + 2 to it, the third call gets passed (3) + 2 , etc. My recursive function prototype looks like this: void calc_rec(int input[], int length, char * previous_string); I wrote a 2 helper functions to help me with the operation, but they implode when I test them: /********************************************************************** * dynamically allocate and append new string to old string and return a pointer to it **********************************************************************/ char * strapp(char * old, char * new) { // find the size of the string to allocate int len = sizeof(char) * (strlen(old) + strlen(new)); // allocate a pointer to the new string char * out = (char*)malloc(len); // concat both strings and return sprintf(out, "%s%s", old, new); return out; } /********************************************************************** * returns a pretty math representation of the calculation op **********************************************************************/ char * mathop(char * old, char operand, int num) { char * output, *newout; char fstr[50]; // random guess.. couldn't think of a better way. sprintf(fstr, " %c %d", operand, num); output = strapp(old, fstr); newout = (char*)malloc( 2*sizeof(char)+sizeof(output) ); sprintf(newout, "(%s)", output); free(output); return newout; } void test_mathop() { int i, total = 10; char * first = "3"; printf("in test_mathop\n"); while (i < total) { first = mathop(first, "+", i); printf("%s\n", first); ++i; } } strapp() returns a pointer to newly appended strings (works), and mathop() is supposed to take the old calculation string ("(3)+2"), a char operand ('+', '-', etc) and an int, and return a pointer to the new string, for example "((3)+2)/3". Any idea where I'm messing things up? thanks.

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• trouble with boost::filesystem::wrecursive_directory_iterator

  - by Dogmatixed

  I'm trying to write a program to help me manage my iTunes library, including removing duplicates and cataloging certain things. At this point I'm still just trying to get it to walk through all the folders, and have run into a problem: I have a small amount of Japanese music, where the artist and/or album is written in Japanese characters. Because of how iTunes arranges things in its library the directories contain these characters. "shouldn't be a problem, though." I thought, because the boost::filesystem library has a wide character version of its recursive iterator. but when I actually try to use it, it seems to completely stop when it hits the first Japanese char. complete stop as in it doesn't finish printing the line, no carriage return or anything. now, I'm still pretty new to programming, so I'm assuming it's my mistake, anyone know why this is happening? here's what I think is the relevant code: fs::wrecursive_directory_iterator end_it; int i; try { for(fs::wrecursive_directory_iterator rec_it(full_path); rec_it != end_it; ++rec_it) { for(i = 0; i < rec_it.level(); i++) { out << "\t"; } out << rec_it->string() << std::endl; } } catch(std::exception e) { out << "something went wrong: " << e.what(); } and from my output file, minus some of the path: /Test Libs/Combine /Test Libs/Lib1 /Test Libs/Lib1/02 Too Long.m4a /Test Libs/Lib1/03 Like a Hitman, Like a Dancer.mp3 /Test Libs/Lib1/A Certain Ratio /Test Libs/Lib1/A Certain Ratio/Beyond Punk! /Test Libs/Lib1/A Certain Ratio/Unknown Album /Test Libs/Lib1/A Certain Ratio/Unknown Album/Do The Du.mp3 /Test Libs/Lib1/A Certain Ratio/Unknown Album/Shack Up.mp3 /Test Libs/Lib1/ finally, what I expect: /Test Libs/Combine /Test Libs/Lib1 /Test Libs/Lib1/02 Too Long.m4a /Test Libs/Lib1/03 Like a Hitman, Like a Dancer.mp3 /Test Libs/Lib1/A Certain Ratio /Test Libs/Lib1/A Certain Ratio/Beyond Punk! /Test Libs/Lib1/A Certain Ratio/Unknown Album /Test Libs/Lib1/A Certain Ratio/Unknown Album/Do The Du.mp3 /Test Libs/Lib1/A Certain Ratio/Unknown Album/Shack Up.mp3 /Test Libs/Lib1/??? /Test Libs/Lib1/Bring it on /Test Libs/Lib1/04 Bring it on.mp3 any thoughts? Thanks.

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• BASH, multiple arrays and a loop.

  - by S1syphus

  At work, we 7 or 8 hardrives we dispatch over the country, each have unique labels which are not sequential. Ideally drives are plugged in our desktop, then gets folders from the server that correspond to the drive name. Sometimes, only one hard drive gets plugged in sometimes multiples, possibly in the future more will be added. Each is mounts to /Volumes/ and it's identifier; so for example /Volumes/f00, where f00 is the identifier. What I want to happen, scan volumes see if any any of the drives are plugged in, then checks the server to see if the folder exists, if ir does copy folder and recursive folders. Here is what I have so far, it checks if the drive exists in Volumes: #!/bin/sh #Declare drives in the array ARRAY=( foo bar long ) #Get the drives from the array DRIVES=${#ARRAY[@]} #Define base dir to check BaseDir="/Volumes" #Define shared server fold on local mount points #I plan to use AFP eventually, but for the sake of ease #using a local mount. ServerMount="BigBlue" #Define folder name for where files are to come from Dispatch="File-Dispatch" dir="$BaseDir/${ARRAY[${i}]}" #Loop through each item in the array and check if exists on /Volumes for (( i=0;i<$DRIVES;i++)); do dir="$BaseDir/${ARRAY[${i}]}" if [ -d "$dir" ]; then echo "$dir exists, you win." else echo "$dir is not attached." fi done What I can't figure out how to do, is how to check the volumes for the server while looping through the harddrive mount points. So I could do something like: #!/bin/sh #Declare drives, and folder location in arrays ARRAY=( foo bar long ) ARRAY1=($(ls ""$BaseDir"/"$ServerMount"/"$Dispatch"")) #Get the drives from the array DRIVES=${#ARRAY[@]} SERVERFOLDER=${#ARRAY1[@]} #Define base dir to check BaseDir="/Volumes" #Define shared server fold on local mount points ServerMount="BigBlue #Define folder name for where files are to come from Dispatch="File-Dispatch" dir="$BaseDir/${ARRAY[${i}]}" #List the contents from server directory into array ARRAY1=($(ls ""$BaseDir"/"$ServerMount"/"$Dispatch"")) echo ${list[@]} for (( i=0;i<$DRIVES;i++)); (( i=0;i<$SERVERFOLDER;i++)); do dir="$BaseDir/${ARRAY[${i}]}" ser="${ARRAY1[${i}]}" if [ "$dir" =~ "$sir" ]; then cp "$sir" "$dir" else echo "$dir is not attached." fi done I know, that is pretty wrong... well very, but I hope it gives you the idea of what I am trying to achieve. Any ideas or suggestions?

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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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• Write Scheme data structures so they can be eval-d back in, or alternative

  - by Jesse Millikan

  I'm writing an application (A juggling pattern animator) in PLT Scheme that accepts Scheme expressions as values for some fields. I'm attempting to write a small text editor that will let me "explode" expressions into expressions that can still be eval'd but contain the data as literals for manual tweaking. For example, (4hss->sexp "747") is a function call that generates a legitimate pattern. If I eval and print that, it becomes (((7 3) - - -) (- - (4 2) -) (- (7 2) - -) (- - - (7 1)) ((4 0) - - -) (- - (7 0) -) (- (7 2) - -) (- - - (4 3)) ((7 3) - - -) (- - (7 0) -) (- (4 1) - -) (- - - (7 1))) which can be "read" as a string, but will not "eval" the same as the function. For this statement, of course, what I need would be as simple as (quote (((7 3... but other examples are non-trivial. This one, for example, contains structs which print as vectors: pair-of-jugglers ; --> (#(struct:hand #(struct:position -0.35 2.0 1.0) #(struct:position -0.6 2.05 1.1) 1.832595714594046) #(struct:hand #(struct:position 0.35 2.0 1.0) #(struct:position 0.6 2.0500000000000003 1.1) 1.308996938995747) #(struct:hand #(struct:position 0.35 -2.0 1.0) #(struct:position 0.6 -2.05 1.1) -1.3089969389957472) #(struct:hand #(struct:position -0.35 -2.0 1.0) #(struct:position -0.6 -2.05 1.1) -1.8325957145940461)) I've thought of at least three possible solutions, none of which I like very much. Solution A is to write a recursive eval-able output function myself for a reasonably large subset of the values that I might be using. There (probably...) won't be any circular references by the nature of the data structures used, so that wouldn't be such a long job. The output would end up looking like `(((3 0) (... ; ex 1 `(,(make-hand (make-position ... ; ex 2 Or even worse if I could't figure out how to do it properly with quasiquoting. Solution B would be to write out everything as (read (open-input-string "(big-long-s-expression)")) which, technically, solves the problem I'm bringing up but is... ugly. Solution C might be a different approach of giving up eval and using only read for parsing input, or an uglier approach where the s-expression is used as directly data if eval fails, but those both seem unpleasant compared to using scheme values directly. Undiscovered Solution D would be a PLT Scheme option, function or library I haven't located that would match Solution A. Help me out before I start having bad recursion dreams again.

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• Dependency Injection and Unit of Work pattern

  - by sunwukung

  I have a dilemma. I've used DI (read: factory) to provide core components for a homebrew ORM. The container provides database connections, DAO's,Mappers and their resultant Domain Objects on request. Here's a basic outline of the Mappers and Domain Object classes class Mapper{ public function __constructor($DAO){ $this->DAO = $DAO; } public function load($id){ if(isset(Monitor::members[$id]){ return Monitor::members[$id]; $values = $this->DAO->selectStmt($id); //field mapping process omitted for brevity $Object = new Object($values); return $Object; } } class User(){ public function setName($string){ $this->name = $string; //mark modified by means fair or foul } } The ORM also contains a class (Monitor) based on the Unit of Work pattern i.e. class Monitor(){ private static array modified; private static array dirty; public function markClean($class); public function markModified($class); } The ORM class itself simply co-ordinates resources extracted from the DI container. So, to instantiate a new User object: $Container = new DI_Container; $ORM = new ORM($Container); $User = $ORM->load('user',1); //at this point the container instantiates a mapper class //and passes a database connection to it via the constructor //the mapper then takes the second argument and loads the user with that id $User->setName('Rumpelstiltskin');//at this point, User must mark itself as "modified" My question is this. At the point when a user sets values on a Domain Object class, I need to mark the class as "dirty" in the Monitor class. I have one of three options as I can see it 1: Pass an instance of the Monitor class to the Domain Object. I noticed this gets marked as recursive in FirePHP - i.e. $this-Monitor-markModified($this) 2: Instantiate the Monitor directly in the Domain Object - does this break DI? 3: Make the Monitor methods static, and call them from inside the Domain Object - this breaks DI too doesn't it? What would be your recommended course of action (other than use an existing ORM, I'm doing this for fun...)

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• Closure Tables - Is this enough data to display a tree view?

  - by James Pitt

  Here is the table I have created by testing the closure table method. | id | parentId | childId | hops | | | | | 270 | 6 | 6 | 0 | 271 | 7 | 7 | 0 | 272 | 8 | 8 | 0 | 273 | 9 | 9 | 0 | 276 | 10 | 10 | 0 | 281 | 9 | 10 | 1 | 282 | 7 | 9 | 1 | 283 | 7 | 10 | 2 | 285 | 7 | 8 | 1 | 286 | 6 | 7 | 1 | 287 | 6 | 9 | 2 | 288 | 6 | 10 | 3 | 289 | 6 | 8 | 2 | 293 | 6 | 9 | 1 | 294 | 6 | 10 | 2 I am trying to create a simple tree of this using PHP. There does not seem to be enough data to create the table. For example, when I look purely at parentId = 6: -Part 6 -Part 7 - ? - ? -Part 9 - ? - ? We know that parts 8 and 10 exists below Part 7 or 9, but not which. We know that part 10 exists at both 3 and 4 nodes deep but where? If I look at other data in the table it is possible to tell it should be: - Part 6 - Part 7 - Part 9 - Part 10 - Part 9 - Part 10 I thought one of the benefits of closure tables was there was no need for recursive queries? Could you help explain what I am doing wrong? EDIT: For clarification, this is a mapping table. There is another table called "parts" which has a column called part_id that correlates to both the parentId and childId columns in the "closure" table. The "id" column in the table above (closure) is just for the purposes of maintaining a primary key. It is not really necessary. The methods I have used to create this closure table is described in the following article: http://dirtsimple.org/2010/11/simplest-way-to-do-tree-based-queries.html EDIT2: It can have two and three hops. I will explain easier by assigning names to the items. Part 6 = Bicycle Part 7 = Gears Part 8 = Chain Part 9 = Bolt Part 10 = Nut Nut is part of Bolt. The Bolt and Nut combo exists directly within Bicycle and within Gears which is part of Bicycle. In relation to what method to use I have looked at Adjacency, Edges, Enum Paths, Closures, DAGS(networks) and the Nested Set Model. I am still trying to work out what is what, but this is an extremely complex component database where there are multiple parents and any modification to a sub-tree must propogate through the other trees. More importantly there will be insertions, deletions and tree views that I wish to avoid recursion during general use, even at the cost of database space and query time during entry.

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• Performance of looping over an Unboxed array in Haskell

  - by Joey Adams

  First of all, it's great. However, I came across a situation where my benchmarks turned up weird results. I am new to Haskell, and this is first time I've gotten my hands dirty with mutable arrays and Monads. The code below is based on this example. I wrote a generic monadic for function that takes numbers and a step function rather than a range (like forM_ does). I compared using my generic for function (Loop A) against embedding an equivalent recursive function (Loop B). Having Loop A is noticeably faster than having Loop B. Weirder, having both Loop A and B together is faster than having Loop B by itself (but slightly slower than Loop A by itself). Some possible explanations I can think of for the discrepancies. Note that these are just guesses: Something I haven't learned yet about how Haskell extracts results from monadic functions. Loop B faults the array in a less cache efficient manner than Loop A. Why? I made a dumb mistake; Loop A and Loop B are actually different. Note that in all 3 cases of having either or both Loop A and Loop B, the program produces the same output. Here is the code. I tested it with ghc -O2 for.hs using GHC version 6.10.4 . import Control.Monad import Control.Monad.ST import Data.Array.IArray import Data.Array.MArray import Data.Array.ST import Data.Array.Unboxed for :: (Num a, Ord a, Monad m) => a -> a -> (a -> a) -> (a -> m b) -> m () for start end step f = loop start where loop i | i <= end = do f i loop (step i) | otherwise = return () primesToNA :: Int -> UArray Int Bool primesToNA n = runSTUArray $ do a <- newArray (2,n) True :: ST s (STUArray s Int Bool) let sr = floor . (sqrt::Double->Double) . fromIntegral $ n+1 -- Loop A for 4 n (+ 2) $ \j -> writeArray a j False -- Loop B let f i | i <= n = do writeArray a i False f (i+2) | otherwise = return () in f 4 forM_ [3,5..sr] $ \i -> do si <- readArray a i when si $ forM_ [i*i,i*i+i+i..n] $ \j -> writeArray a j False return a primesTo :: Int -> [Int] primesTo n = [i | (i,p) <- assocs . primesToNA $ n, p] main = print $ primesTo 30000000

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• Recursion problem; completely lost

  - by timeNomad

  So I've been trying to solve this assignment whole day, just can't get it. The following function accepts 2 strings, the 2nd (not 1st) possibly containing *'s (asterisks). An * is a replacement for a string (empty, 1 char or more), it can appear appear (only in s2) once, twice, more or not at all, it cannot be adjacent to another * (ab**c), no need to check that. public static boolean samePattern(String s1, String s2) It returns true if strings are of the same pattern. It must be recursive, not use any loops, static & global variables. Can use local variables & method overloading. Can use only these methods: charAt(i), substring(i), substring(i, j), length(). Examples: 1: TheExamIsEasy; 2: "The*xamIs*y" --- true 1: TheExamIsEasy; 2: "Th*mIsEasy*" --- true 1: TheExamIsEasy; 2: "*" --- true 1: TheExamIsEasy; 2: "TheExamIsEasy" --- true 1: TheExamIsEasy; 2: "The*IsHard" --- FALSE I tried comparing the the chars one by one using charAt until an asterisk is encountered, then check if the asterisk is an empty one by comparing is successive char (i+1) with the char of s1 at position i, if true -- continue recursion with i+1 as counter for s2 & i as counter for s1; if false -- continue recursion with i+1 as counters for both. Continue this until another asterisk is found or end of string. I dunno, my brain loses track of things, can't concentrate, any pointers / hints? Am I in the right direction? Also, it's been told that a backtracking technique is to be used to solve this. My code so far (doesn't do the job, even theoretically): public static boolean samePattern(String s1, String s2) { if (s1.equals(s2) || s2 == "*") { return true; } return samePattern(s1, s2, 1); } public static boolean samePattern(String s1, String s2, int i) { if (s1.equals(s2)) return true; if (i == s2.length() - 1) // No *'s found -- not same pattern. return false; if (s1.substring(0, i).equals(s2.substring(0, i))) samePattern(s1, s2, i+1); else if (s2.charAt(i-1) == '*') samePattern(s1.substring(0, i-1), s2.substring(0, i), 1); // new smaller strings. else samePattern(s1.substring(1), s2, i); }

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• How to find the one Label in DataList that is set to True

  - by Doug

  In my .aspx page I have my DataList: <asp:DataList ID="DataList1" runat="server" DataKeyField="ProductSID" DataSourceID="SqlDataSource1" onitemcreated="DataList1_ItemCreated" RepeatColumns="3" RepeatDirection="Horizontal" Width="1112px"> <ItemTemplate> ProductSID: <asp:Label ID="ProductSIDLabel" runat="server" Text='<%# Eval("ProductSID") %>' /> <br /> ProductSKU: <asp:Label ID="ProductSKULabel" runat="server" Text='<%# Eval("ProductSKU") %>' /> <br /> ProductImage1: <asp:Label ID="ProductImage1Label" runat="server" Text='<%# Eval("ProductImage1") %>' /> <br /> ShowLive: <asp:Label ID="ShowLiveLabel" runat="server" Text='<%# Eval("ShowLive") %>' /> <br /> CollectionTypeID: <asp:Label ID="CollectionTypeIDLabel" runat="server" Text='<%# Eval("CollectionTypeID") %>' /> <br /> CollectionHomePage: <asp:Label ID="CollectionHomePageLabel" runat="server" Text='<%# Eval("CollectionHomePage") %>' /> <br /> <br /> </ItemTemplate> </asp:DataList> And in my code behind using the ItemCreated event to find and set the label.backcolor property. (Note:I'm using a recursive findControl class) protected void DataList1_ItemCreated(object sender, DataListItemEventArgs e) { foreach (DataListItem item in DataList1.Items) { if (e.Item.ItemType == ListItemType.Item || e.Item.ItemType == ListItemType.AlternatingItem) { Label itemLabel = form1.FindControlR("CollectionHomePageLabel") as Label; if (itemLabel !=null || itemLabel.Text == "True") { itemLabel.BackColor = System.Drawing.Color.Yellow; } } When I run the page, the itemLabel is found, and the color shows. But it sets the itemLabel color to the first instance of the itemLabel found in the DataList. Of all the itemLabels in the DataList, only one will have it's text = True - and that should be the label picking up the backcolor. Also: The itemLabel is picking up a column in the DB called "CollectionHomePage" which is True/False bit data type. I must be missing something simple... Thanks for your ideas.

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• Stepping into Ruby Meta-Programming: Generating proxy methods for multiple internal methods

  - by mstksg

  Hi all; I've multiply heard Ruby touted for its super spectacular meta-programming capabilities, and I was wondering if anyone could help me get started with this problem. I have a class that works as an "archive" of sorts, with internal methods that process and output data based on an input. However, the items in the archive in the class itself are represented and processed with integers, for performance purposes. The actual items outside of the archive are known by their string representation, which is simply number_representation.to_s(36). Because of this, I have hooked up each internal method with a "proxy method" that converts the input into the integer form that the archive recognizes, runs the internal method, and converts the output (either a single other item, or a collection of them) back into strings. The naming convention is this: internal methods are represented by _method_name; their corresponding proxy method is represented by method_name, with no leading underscore. For example: class Archive ## PROXY METHODS ## ## input: string representation of id's ## output: string representation of id's def do_something_with id result = _do_something_with id.to_i(36) return nil if result == nil return result.to_s(36) end def do_something_with_pair id_1,id_2 result = _do_something_with_pair id_1.to_i(36), id_2.to_i(36) return nil if result == nil return result.to_s(36) end def do_something_with_these ids result = _do_something_with_these ids.map { |n| n.to_i(36) } return nil if result == nil return result.to_s(36) end def get_many_from id result = _get_many_from id return nil if result == nil # no sparse arrays returned return result.map { |n| n.to_s(36) } end ## INTERNAL METHODS ## ## input: integer representation of id's ## output: integer representation of id's def _do_something_with id # does something with one integer-represented id, # returning an id represented as an integer end def do_something_with_pair id_1,id_2 # does something with two integer-represented id's, # returning an id represented as an integer end def _do_something_with_these ids # does something with multiple integer ids, # returning an id represented as an integer end def _get_many_from id # does something with one integer-represented id, # returns a collection of id's represented as integers end end There are a couple of reasons why I can't just convert them if id.class == String at the beginning of the internal methods: These internal methods are somewhat computationally-intensive recursive functions, and I don't want the overhead of checking multiple times at every step There is no way, without adding an extra parameter, to tell whether or not to re-convert at the end I want to think of this as an exercise in understanding ruby meta-programming Does anyone have any ideas? edit The solution I'd like would preferably be able to take an array of method names @@PROXY_METHODS = [:do_something_with, :do_something_with_pair, :do_something_with_these, :get_many_from] iterate through them, and in each iteration, put out the proxy method. I'm not sure what would be done with the arguments, but is there a way to test for arguments of a method? If not, then simple duck typing/analogous concept would do as well.

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• Hibernate3: Self-Referencing Objects

  - by monojohnny

  Need some help on understanding how to do this; I'm going to be running recursive 'find' on a file system and I want to keep the information in a single DB table - with a self-referencing hierarchial structure: This is my DB Table structure I want to populate. DirObject Table: id int NOT NULL, name varchar(255) NOT NULL, parentid int NOT NULL); Here is the proposed Java Class I want to map (Fields only shown): public DirObject { int id; String name; DirObject parent; ... For the 'root' directory was going to use parentid=0; real ids will start at 1, and ideally I want hibernate to autogenerate the ids. Can somebody provide a suggested mapping file for this please; as a secondary question I thought about doing the Java Class like this instead: public DirObject { int id; String name; List<DirObject> subdirs; Could I use the same data model for either of these two methods ? (With a different mapping file of course). --- UPDATE: so I tried the mapping file suggested below (thanks!), repeated here for reference: <hibernate-mapping> <class name="my.proj.DirObject" table="category"> ... <set name="subDirs" lazy="true" inverse="true"> <key column="parentId"/> <one-to-many class="my.proj.DirObject"/> </set> <many-to-one name="parent" class="my.proj.DirObject" column="parentId" cascade="all" /> </class> ...and altered my Java class to have BOTH 'parentid' and 'getSubDirs' [returning a 'HashSet']. This appears to work - thanks, but this is the test code I used to drive this - I think I'm not doing something right here, because I thought Hibernate would take care of saving the subordinate objects in the Set without me having to do this explicitly ? DirObject dirobject=new DirObject(); dirobject.setName("/files"); dirobject.setParent(dirobject); DirObject d1, d2; d1=new DirObject(); d1.setName("subdir1"); d1.setParent(dirobject); d2=new DirObject(); d2.setName("subdir2"); d2.setParent(dirobject); HashSet<DirObject> subdirs=new HashSet<DirObject>(); subdirs.add(d1); subdirs.add(d2); dirobject.setSubdirs(subdirs); session.save(dirobject); session.save(d1); session.save(d2);

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• GHC.Generics and Type Families

  - by jberryman

  This is a question related to my module here, and is simplified a bit. It's also related to this previous question, in which I oversimplified my problem and didn't get the answer I was looking for. I hope this isn't too specific, and please change the title if you can think if a better one. Background My module uses a concurrent chan, split into a read side and write side. I use a special class with an associated type synonym to support polymorphic channel "joins": {-# LANGUAGE TypeFamilies #-} class Sources s where type Joined s newJoinedChan :: IO (s, Messages (Joined s)) -- NOT EXPORTED --output and input sides of channel: data Messages a -- NOT EXPORTED data Mailbox a instance Sources (Mailbox a) where type Joined (Mailbox a) = a newJoinedChan = undefined instance (Sources a, Sources b)=> Sources (a,b) where type Joined (a,b) = (Joined a, Joined b) newJoinedChan = undefined -- and so on for tuples of 3,4,5... The code above allows us to do this kind of thing: example = do (mb , msgsA) <- newJoinedChan ((mb1, mb2), msgsB) <- newJoinedChan --say that: msgsA, msgsB :: Messages (Int,Int) --and: mb :: Mailbox (Int,Int) -- mb1,mb2 :: Mailbox Int We have a recursive action called a Behavior that we can run on the messages we pull out of the "read" end of the channel: newtype Behavior a = Behavior (a -> IO (Behavior a)) runBehaviorOn :: Behavior a -> Messages a -> IO () -- NOT EXPORTED This would allow us to run a Behavior (Int,Int) on either of msgsA or msgsB, where in the second case both Ints in the tuple it receives actually came through separate Mailboxes. This is all tied together for the user in the exposed spawn function spawn :: (Sources s) => Behavior (Joined s) -> IO s ...which calls newJoinedChan and runBehaviorOn, and returns the input Sources. What I'd like to do I'd like users to be able to create a Behavior of arbitrary product type (not just tuples) , so for instance we could run a Behavior (Pair Int Int) on the example Messages above. I'd like to do this with GHC.Generics while still having a polymorphic Sources, but can't manage to make it work. spawn :: (Sources s, Generic (Joined s), Rep (Joined s) ~ ??) => Behavior (Joined s) -> IO s The parts of the above example that are actually exposed in the API are the fst of the newJoinedChan action, and Behaviors, so an acceptable solution can modify one or all of runBehaviorOn or the snd of newJoinedChan. I'll also be extending the API above to support sums (not implemented yet) like Behavior (Either a b) so I hoped GHC.Generics would work for me. Questions Is there a way I can extend the API above to support arbitrary Generic a=> Behavior a? If not using GHC's Generics, are there other ways I can get the API I want with minimal end-user pain (i.e. they just have to add a deriving clause to their type)?

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• All possible combinations of length 8 in a 2d array

  - by CodeJunki

  Hi, I've been trying to solve a problem in combinations. I have a matrix 6X6 i'm trying to find all combinations of length 8 in the matrix. I have to move from neighbor to neighbor form each row,column position and i wrote a recursive program which generates the combination but the problem is it generates a lot of duplicates as well and hence is inefficient. I would like to know how could i eliminate calculating duplicates and save time. int a={{1,2,3,4,5,6}, {8,9,1,2,3,4}, {5,6,7,8,9,1}, {2,3,4,5,6,7}, {8,9,1,2,3,4}, {5,6,7,8,9,1}, } void genSeq(int row,int col,int length,int combi) { if(length==8) { printf("%d\n",combi); return; } combi = (combi * 10) + a[row][col]; if((row-1)>=0) genSeq(row-1,col,length+1,combi); if((col-1)>=0) genSeq(row,col-1,length+1,combi); if((row+1)<6) genSeq(row+1,col,length+1,combi); if((col+1)<6) genSeq(row,col+1,length+1,combi); if((row+1)<6&&(col+1)<6) genSeq(row+1,col+1,length+1,combi); if((row-1)>=0&&(col+1)<6) genSeq(row-1,col+1,length+1,combi); if((row+1)<6&&(row-1)>=0) genSeq(row+1,col-1,length+1,combi); if((row-1)>=0&&(col-1)>=0) genSeq(row-1,col-1,length+1,combi); } I was also thinking of writing a dynamic program basically recursion with memorization. Is it a better choice?? if yes than I'm not clear how to implement it in recursion. Have i really hit a dead end with approach??? Thankyou Edit Eg result 12121212,12121218,12121219,12121211,12121213. the restrictions are that you have to move to your neighbor from any point, you have to start for each position in the matrix i.e each row,col. you can move one step at a time, i.e right, left, up, down and the both diagonal positions. Check the if conditions. i.e if your in (0,0) you can move to either (1,0) or (1,1) or (0,1) i.e three neighbors. if your in (2,2) you can move to eight neighbors. so on...

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• Haskell type classes and type families (cont'd)

  - by Giuseppe Maggiore

  I need some help in figuring a compiler error which is really driving me nuts... I have the following type class: infixl 7 --> class Selectable a s b where type Res a s b :: * (-->) :: (CNum n) => (Reference s a) -> (n,(a->b),(a->b->a)) -> Res a s b which I instance twice. First time goes like a charm: instance Selectable a s b where type Res a s b = Reference s b (-->) (Reference get set) (_,read,write) = (Reference (\s -> let (v,s') = get s in (read v,s')) (\s -> \x -> let (v,s') = get s v' = write v x (_,s'') = set s' v' in (x,s''))) since the type checker infers (-->) :: Reference s a -> (n,a->b,a->b->a) -> Reference s b and this signature matches with the class signature for (--) since Res a s b = Reference s b Now I add a second instance and everything breaks: instance (Recursive a, Rec a ~ reca) => Selectable a s (Method reca b c) where type Res a s (Method reca b c) = b -> Reference s c (-->) (Reference get set) (_,read,write) = \(x :: b) -> from_constant( Constant(\(s :: s)-> let (v,s') = get s :: (a,s) m = read v ry = m x :: Reference (reca) c (y,v') = getter ry (cons v) :: (c,reca) v'' = elim v' (_,s'') = set s' v'' in (y,s''))) :: Reference s c the compiler complains that Couldn't match expected type `Res a s (Method reca b c)' against inferred type `b -> Reference s c' The lambda expression `\ (x :: b) -> ...' has one argument, which does not match its type In the expression: \ (x :: b) -> from_constant (Constant (\ (s :: s) -> let ... in ...)) :: Reference s c In the definition of `-->': --> (Reference get set) (_, read, write) = \ (x :: b) -> from_constant (Constant (\ (s :: s) -> ...)) :: Reference s c reading carefully the compiler is telling me that it has inferred the type of (--) thusly: (-->) :: Reference s a -> (n,a->(Method reca b c),a->(Method reca b c)->a) -> (b -> Reference s c) which is correct since Res a s (Method reca b c) = b -> Reference s c but why can't it match the two definitions? Sorry for not offering a more succint and standalone example, but in this case I cannot figure how to do it...

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• Avoiding explicit recursion in Haskell

  - by Travis Brown

  The following simple function applies a given monadic function iteratively until it hits a Nothing, at which point it returns the last non-Nothing value. It does what I need, and I understand how it works. lastJustM :: (Monad m) => (a -> m (Maybe a)) -> a -> m a lastJustM g x = g x >>= maybe (return x) (lastJustM g) As part of my self-education in Haskell I'm trying to avoid explicit recursion (or at least understand how to) whenever I can. It seems like there should be a simple non-explicitly recursive solution in this case, but I'm having trouble figuring it out. I don't want something like a monadic version of takeWhile, since it could be expensive to collect all the pre-Nothing values, and I don't care about them anyway. I checked Hoogle for the signature and nothing shows up. The m (Maybe a) bit makes me think a monad transformer might be useful here, but I don't really have the intuitions I'd need to come up with the details (yet). It's probably either embarrassingly easy to do this or embarrassingly easy to see why it can't or shouldn't be done, but this wouldn't be the first time I've used self-embarrassment as a pedagogical strategy. Background: Here's a simplified working example for context: suppose we're interested in random walks in the unit square, but we only care about points of exit. We have the following step function: randomStep :: (Floating a, Ord a, Random a) => a -> (a, a) -> State StdGen (Maybe (a, a)) randomStep s (x, y) = do (a, gen') <- randomR (0, 2 * pi) <$> get put gen' let (x', y') = (x + s * cos a, y + s * sin a) if x' < 0 || x' > 1 || y' < 0 || y' > 1 then return Nothing else return $ Just (x', y') Something like evalState (lastJustM (randomStep 0.01) (0.5, 0.5)) <$> newStdGen will give us a new data point.

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• Why did File::Find finish short of completely traversing a large directory?

  - by Stan

  A directory exists with a total of 2,153,425 items (according to Windows folder Properties). It contains .jpg and .gif image files located within a few subdirectories. The task was to move the images into a different location while querying each file's name to retrieve some relevant info and store it elsewhere. The script that used File::Find finished at 20462 files. Out of curiosity I wrote a tiny recursive function to count the items which returned a count of 1,734,802. I suppose the difference can be accounted for by the fact that it didn't count folders, only files that passed the -f test. The problem itself can be solved differently by querying for file names first instead of traversing the directory. I'm just wondering what could've caused File::Find to finish at a small fraction of all files. The data is stored on an NTFS file system. Here is the meat of the script; I don't think including DBI stuff would be relevant since I reran the script with nothing but a counter in process_img() which returned the same number. find(\&process_img, $path_from); sub process_img { eval { return if ($_ eq "." or $_ eq ".."); ## Omitted querying and composing new paths for brevity. make_path("$path_to\\img\\$dir_area\\$dir_address\\$type"); copy($File::Find::name, "$path_to\\img\\$dir_area\\$dir_address\\$type\\$new_name"); }; if ($@) { print STDERR "eval barks: $@\n"; return } } And here is another method I used to count files: count_images($path_from); sub count_images { my $path = shift; opendir my $images, $path or die "died opening $path"; while (my $item = readdir $images) { next if $item eq '.' or $item eq '..'; $img_counter++ && next if -f "$path/$item"; count_images("$path/$item") if -d "$path/$item"; } closedir $images or die "died closing $path"; } print $img_counter;

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• Deleting a node in a family tree

  - by user559142

  Hi, I'm trying to calclulate the best way to delete a node in a family tree. First, a little description of how the app works. My app makes the following assumption: Any node can only have one partner. That means that any child a single node has, it will also be the partner nodes child too. Therefore, step relations, divorces etc aren't compensated for. A node always has two parents - A mother and father cannot be added seperately. If the user doesn't know the details - the nodes attributes are set to a default value. Also any node can add parents, siblings, children to itself. Therefore in law relationships can be added. I have the following classes: FamilyMember String fName; String lName; String dob; String gender; FamilyMember mother, father, partner; ArrayListchildren; int index; int generation; void linkParents(); void linkPartner(); void addChild(); //gets & sets for fields Family ArrayListfamily; void addMember(); void removeMember(); FamilyMember getFamilyMember(index); ArrayListgetFamilyMembers(); FamilyTree Family family; void removeMember(); //need help void displayFamilyMembers(); void addFamilyMember(); void enterDetails(); void displayAncestors(); void displayDescendants(); void printDescendants(); FamilyMember findRootNode(); void sortGenerations(); void getRootGeneration(); I am having trouble with identifying the logic for removing a member. All other functions work fine. Has anyone developed a family tree app before who knows how to deal with removing various different nodes in the family "tree"? e.g. removing a leaf removing a leaf with partner (what if partner has parents etc) removing a parent It seems to be another recursive property but my head is swelling from over thought.

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• color letters in a div

  - by Growler

  I've created a palindrome checker. I want to take it one step further and show the letters being compared as it is being checked. HTML: <p id="typing"></p> <input type="text" id="textBox" onkeyup="pal(this.value);" value="" /> <div id="response"></div> <hr> <div id="palindromeRun"></div> JS: To do this, I run the recursive check... Then if it is a palindrome, I run colorLetters(), which I'm trying to highlight in green each letter as it is being checked. Right now it is just rewriting palindromeRun's HTML with the first letter. I know this is because of the way I'm resetting its HTML. I don't know how to just grab the first and last letter, change only those letters' css, then increment i and j on the next setTimeout loop. var timeout2 = null; function pal (input) { var str = input.replace(/\s/g, ''); var str2 = str.replace(/\W/, ''); if (checkPal(str2, 0, str2.length-1)) { $("#textBox").css({"color" : "green"}); $("#response").html(input + " is a palindrome"); $("#palindromeRun").html(input); colorLetters(str2, 0, str2.length-1); } else { $("#textBox").css({"color" : "red"}); $("#response").html(input + " is not a palindrome"); } if (input.length <= 0) { $("#response").html(""); $("#textBox").css({"color" : "black"}); } } function checkPal (input, i, j) { if (input.length <= 1) { return false; } if (i === j || ((j-i) == 1 && input.charAt(i) === input.charAt(j))) { return true; } else { if (input.charAt(i).toLowerCase() === input.charAt(j).toLowerCase()) { return checkPal(input, ++i, --j); } else { return false; } } } function colorLetters(myinput, i, j) { if (timeout2 == null) { timeout2 = setTimeout(function () { console.log("called"); var firstLetter = $("#palindromeRun").html(myinput.charAt(i)) var secondLetter = $("#palindromeRun").html(myinput.charAt(j)) $(firstLetter).css({"color" : "red"}); $(secondLetter).css({"color" : "green"}); i++; j++; timeout2=null; }, 1000); } } Secondary: If possible, I'd just like to have it colors the letters as the user is typing... I realize this will require a setTimeout on each keyup, but also am not sure how to write this.

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• DFS Backtracking with java

  - by Cláudio Ribeiro

  I'm having problems with DFS backtracking in an adjacency matrix. Here's my code: (i added the test to the main in case someone wants to test it) public class Graph { private int numVertex; private int numEdges; private boolean[][] adj; public Graph(int numVertex, int numEdges) { this.numVertex = numVertex; this.numEdges = numEdges; this.adj = new boolean[numVertex][numVertex]; } public void addEdge(int start, int end){ adj[start-1][end-1] = true; adj[end-1][start-1] = true; } List<Integer> visited = new ArrayList<Integer>(); public Integer DFS(Graph G, int startVertex){ int i=0; if(pilha.isEmpty()) pilha.push(startVertex); for(i=1; i<G.numVertex; i++){ pilha.push(i); if(G.adj[i-1][startVertex-1] != false){ G.adj[i-1][startVertex-1] = false; G.adj[startVertex-1][i-1] = false; DFS(G,i); break; }else{ visited.add(pilha.pop()); } System.out.println("Stack: " + pilha); } return -1; } Stack<Integer> pilha = new Stack(); public static void main(String[] args) { Graph g = new Graph(6, 9); g.addEdge(1, 2); g.addEdge(1, 5); g.addEdge(2, 4); g.addEdge(2, 5); g.addEdge(2, 6); g.addEdge(3, 4); g.addEdge(3, 5); g.addEdge(4, 5); g.addEdge(6, 4); g.DFS(g, 1); } } I'm trying to solve the euler path problem. the program solves basic graphs but when it needs to backtrack, it just does not do it. I think the problem might be in the stack manipulations or in the recursive dfs call. I've tried a lot of things, but still can't seem to figure out why it does not backtrack. Can somebody help me ?

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• Inbreeding-immune database structure

  - by Nick Savage

  I have an application that requires a "simple" family tree. I would like to be able to perform queries that will give me data for an entire family given one id from a member in the family. I say simple because it does not need to take into account adoption or any other obscurities. The requirements for the application are as follows: Any two people will not be able to breed if they're from the same genetic line Needs to allow for the addition of new family lines (new people with no previous family) Need to be able to pull siblings, parents separately through queries I'm having trouble coming up with the proper structure for the database. So far I've come up with two solutions but they're not very reliable and will probably get out of hand quite quickly. Solution 1 involves placing a family_ids field on the people table and storing a list of unique family ids. Each time two people breed the lists are checked against each other to make sure no ids match and if everything checks out will merge the two lists and set that as the child's family_ids field. Example: Father (family_ids: (null)) breeds with Mother (family_ids: (213, 519)) -> Child (family_ids: (213, 519)) breeds with Random Person (family_ids: (813, 712, 122, 767)) -> Grandchild (family_ids: (213, 519, 813, 712, 122, 767)) And so on and so forth... The problem I see with this is the lists becoming unreasonably large as time goes on. Solution 2 uses cakephp's associations to declare: public $belongsTo = array( 'Father' => array( 'className' => 'User', 'foreignKey' => 'father_id' ), 'Mother' => array( 'className' => 'User', 'foreignKey' => 'mother_id' ) ); Now setting recursive to 2 will fetch the results of the mother and father, along with their mother and father, and so on and so forth all the way down the line. The problem with this route is that the data is in nested arrays and I'm unsure of how to efficiently work through the code. If anyone would be able to steer me in the direction of the most efficient way to handle what I want to achieve that would be tremendously helpful. Any and all help is greatly appreciated and I'll gladly answer any questions anyone has. Thanks a lot.

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