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• Card deck and sparse matrix interview questions

  - by MrDatabase

  I just had a technical phone screen w/ a start-up. Here's the technical questions I was asked ... and my answers. What do think of these answers? Feel free to post better answers :-) Question 1: how would you represent a standard 52 card deck in (basically any language)? How would you shuffle the deck? Answer: use an array containing a "Card" struct or class. Each instance of card has some unique identifier... either it's position in the array or a unique integer member variable in the range [0, 51]. Shuffle the cards by traversing the array once from index zero to index 51. Randomly swap ith card with "another card" (I didn't remember how this shuffle algorithm works exactly). Watch out for using the same probability for each card... that's a gotcha in this algorithm. I mentioned the algorithm is from Programming Pearls. Question 2: how to represent a large sparse matrix? the matrix can be very large... like 1000x1000... but only a relatively small number (~20) of the entries are non-zero. Answer: condense the array into a list of the non-zero entries. for a given entry (i,j) in the array... "map" (i,j) to a single integer k... then use k as a key into a dictionary or hashtable. For the 1000x1000 sparse array map (i,j) to k using something like f(i, j) = i + j * 1001. 1001 is just one plus the maximum of all i and j. I didn't recall exactly how this mapping worked... but the interviewer got the idea (I think). Are these good answers? I'm wondering because after I finished the second question the interviewer said the dreaded "well that's all the questions I have for now." Cheers!

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• How to determine where on a path my object will be at a given point in time?

  - by Dave

  I have map and an obj that is meant to move from start to end in X amount of time. The movements are all straight lines, as curves are beyond my ability at the moment. So I am trying to get the object to move from these points, but along the way there are way points which keep it on a given path. The speed of the object is determined by how long it will take to get from start to end (based on X). This is what i have so far: //get_now() returns seconds since epoch var timepassed = get_now() - myObj[id].start; //seconds since epoch for departure var timeleft = myObj[id].end - get_now(); //seconds since epoch for arrival var journey_time = 60; //this means 60 minutes total journey time var array = [[650,250]]; //way points along the straight paths if(step == 0 || step =< array.length){ var destinationx = array[step][0]; var destinationy = array[step][1]; }else if( step == array.length){ var destinationx = 250; var destinationy = 100; } else { var destinationx = myObj[id].startx; var destinationy = myObj[id].starty; } step++; When the user logs in at any given time, the object needs to be drawn in the correct place of the path, almost as if its been travelling along the path whilst the user has not been at the PC with the available information i have above. How do I do this? Note: The camera angle in the game is a birds eye view so its a straight forward X:Y rather than isometric angles.

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• Can I rebuild degraded RAID1 on a SAS 5 i controller with a larger mirror drive size?

  - by Kenny

  Hi, A drive failed on a Dell SAS 5i controller - see controller bios screengrab: http://imagebin.ca/view/SkZbszA.html The primary is a 160GB 10k sata drive. I added a 250GB 7k rpm drive in the hope that the array would rebuild onto this drive. This did not happen. (assuming that the controller would just operate at the speed of the slowest drive) The controller could see the new drive, but it didn't automatically rebuild the raid1 onto this drive. (my assumption is that it did not do this rebuild as the drive sizes are different). There was an option to add the new drive to the existing raid1 array - but when I tried this a message appeared stating that all data on the array would be lost. (I didn't get a screenshot of this message, I will later) Should the SAS 5i allow me to rebuild the array onto a larger drive? Is the option to add the drive to the array the right way to go? Many thanks!

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• i need ur help [closed]

  - by aisha khan

  Write a program that prompts the user to enter the size of the array, allocate memory using malloc(), ask the user to enter elements of the array and displays if the puzzle is solvable. As part of this program, write a recursive function int Solvable(int start, int squares[]) that takes a starting position of the marker along with the array of squares. The function should return 1 if it is possible to solve the puzzle from the starting configuration and 0 if it is impossible

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• Elo system behaves oddly in program I've created

  - by adc

  Alright, so I'm looking to build a small program (C# and XAML) that, essentially, does this: Generate array of players. Each player has a current rating and a true rating. I set current rating to 1200 as a starting point right now; I've also tried setting it to true rating and the average of the two. True rating is what their skill level actually is. Their true rating is calculated based on percentages from the current League of Legends rating system; generating an array of 970 thousand generates results very similar to the data from here: (removed due to URL limit - but trust me, the results are very similar). This array is of length specified by the user. If need be, sort the array from smallest to largest. Play X number of games, again specified by the user. This is done by taking the array of players (which is sorted by Current Rating after being created) and running through it in groups of 10. The first five are on team one, the second five are on team two. It then takes the True Rating of these players and calculates an expected chance to win using the Elo system. It generates a random double and compares it to the expected chance to win; if the number is lower, team one wins - otherwise team two wins. I then update the rating of the players via, again, the Elo system - giving the winning team a score of 1 and the losing team a score of 0. I use a K value of 36 (but have tried 12, 24, and even higher ones) and an F value of 400. After going through the entire loop of players (which I have conveniently forced to be a multiple of ten), it sorts the array - again via current rating. This, if my understanding of the Elo system is correct, runs properly. However, it doesn't seem to work. I have a running test telling me how many players of the full array are within 100 current rating of their true rating. I would expect some portion of the population to be outside this range (as probability is not always going to go in their favor), but a full 40-45% of the population is outside of this range. I also have it outputting the maximum difference between true and current rating - and I have never seen this drop below 500! It hovers between 550-600, occasionally going over or under. I'm at a loss as to what to change - I've fiddled with the K and F values, where I start all the players, etc. but nothing changes the fact that eventually a good 40% of the population is outside the range. And it isn't that I have it playing too few games - it's now run through over 60 thousand games and the problem never disappears or really fluctuates. The full C# code, including everything except the XAML file and the Player class (pastebin is being very slow and I can only post two links, so I can't link to the XAML file): http://pastebin.com/rFcZRL84 The Player class: http://pastebin.com/4cJTdTRu I guess my question is did I do anything wrong? Is there a problem with the way I implemented the system, or is it just that Riot uses a significantly modified Elo system? I don't think it's the latter, as that still wouldn't explain the massive true and current rating differences to me, however.

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• libgdx arrays onTouch() method and delays for objects

  - by johnny-b

  i am trying to create random bullets but it is not working for some reason. also how can i make a delay so the bullets come every 30 seconds or 1 minute???? also the onTouch method does not work and it is not taking the bullet away???? shall i put the array in the GameRender class? thanks public class GameWorld { public static Ball ball; private Bullet bullet1; private ScrollHandler scroller; private Array<Bullet> bullets = new Array<Bullet>(); public GameWorld() { ball = new Ball(280, 273, 32, 32); bullet = new Bullet(-300, 200); scroller = new ScrollHandler(0); bullets.add(new Bullet(bullet.getX(), bullet.getY())); bullets = new Array<Bullet>(); Bullet bullet = null; float bulletX = 0.0f; float bulletY = 0.0f; for (int i=0; i < 10; i++) { bulletX = MathUtils.random(-10, 10); bulletY = MathUtils.random(-10, 10); bullet = new Bullet(bulletX, bulletY); bullets.add(bullet); } } public void update(float delta) { ball.update(delta); bullet.update(delta); scroller.update(delta); } public static Ball getBall() { return ball; } public ScrollHandler getScroller() { return scroller; } public Bullet getBullet1() { return bullet1; } } i also tried this and it is not working, i used this in the GameRender class Array<Bullet> enemies=new Array<Bullet>(); //in the constructor of the class enemies.add(new Bullet(bullet.getX(), bullet.getY())); // this throws an exception for some reason??? this is in the render method for(int i=0; i<bullet.size; i++) bullet.get(i).draw(batcher); //this i am using in any method that will allow me from the constructor to update to render for(int i=0; i<bullet.size; i++) bullet.get(i).update(delta); this is not taking the bullet out @Override public boolean touchDown(int screenX, int screenY, int pointer, int button) { for(int i=0; i<bullet.size; i++) if(bullet.get(i).getBounds().contains(screenX,screenY)) bullet.removeIndex(i--); return false; } thanks for the help anyone.

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• MD3200i Slow Performance and Queue Depth

  - by Caleb_S

  Read performance on our SAN is slow under certain workloads. When we compare this to some local storage, we find the local storage performing 2x as fast. The SAN performs well with a high Queue Depth, and poorly with a low queue depth. However, the local storage performs well with a low Queue Depth. I'd like to know the reason for this occurring and find out what the specific limiting factor is in this situation. MD3200i iSCSI SAN ($15,000) 6 x 600GB 15k SAS RAID5 6 x 2TB 7.2k NLS RAID5 XCOPY /j Benchmark: (Slow) 15k Array - 71MB/s (Queue Depth 1) 7.2k Array- 71MB/s (Queue Depth 1) Robycopy /MT:32 Benchmark: (Fast) 15k Array - 171MB/s (Queue Depth ~12) 7.2k Array- 128MB/s (Queue Depth ~12) , , Read Performance on a Local controller is fast under the workload the SAN is slow at. , HighPoint 2230 RAID Controller ($600) 4 x 1TB 7.2k SATA RAID5 XCOPY /j Benchmark: 7.2k Array - 145MB/s (Queue Depth 1) (appears to max out the SATA bus)

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• Why the overhead when allocating objects/arrays in Java?

  - by Gnijuohz

  How many bytes an array occupies in Java? Assume It's a 64bit machine and also assume there are N elements in an array, so all these elements would take up 2*N, 4*N or 8*N bytes for different types of array. And a lecture in Coursera says that it would occupy 2*N+24, 4*N+24 or 8*N+24 bytes for a N element array and the 24 bytes is called overhead, but didn't explain why the overhead is needed. Also objects have overheads, which is 16 bytes. What exactly are these overheads? What are these 24/16 bytes composed of? Also, do these overheads only exist in Java? How about C, C++ and Python?

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• Avoiding coupling

  - by Seralize

  It is also true that a system may become so coupled, where each class is dependent on other classes that depend on other classes, that it is no longer possible to make a change in one place without having a ripple effect and having to make subsequent changes in many places.[1] This is why using an interface or an abstract class can be valuable in any object-oriented software project. Quote from Wikipedia Starting from scratch I'm starting from scratch with a project that I recently finished because I found the code to be too tightly coupled and hard to refactor, even when using MVC. I will be using MVC on my new project aswell but want to try and avoid the pitfalls this time, hopefully with your help. Project summary My issue is that I really wish to keep the Controller as clean as possible, but it seems like I can't do this. The basic idea of the program is that the user picks wordlists which is sent to the game engine. It will pick random words from the lists until there are none left. Problem at hand My main problem is that the game will have 'modes', and need to check the input in different ways through a method called checkWord(), but exactly where to put this and how to abstract it properly is a challenge to me. I'm new to design patterns, so not sure whether there exist any might fit my problem. My own attempt at abstraction Here is what I've gotten so far after hours of 'refactoring' the design plans, and I know it's long, but it's the best I could do to try and give you an overview (Note: As this is the sketch, anything is subject to change, all help and advice is very welcome. Also note the marked coupling points): Wordlist class Wordlist { // Basic CRUD etc. here! // Other sample methods: public function wordlistCount($user_id) {} // Returns count of how many wordlists a user has public function getAll($user_id) {} // Returns all wordlists of a user } Word class Word { // Basic CRUD etc. here! // Other sample methods: public function wordCount($wordlist_id) {} // Returns count of words in a wordlist public function getAll($wordlist_id) {} // Returns all words from a wordlist public function getWordInfo($word_id) {} // Returns information about a word } Wordpicker class Wordpicker { // The class needs to know which words and wordlists to exclude protected $_used_words = array(); protected $_used_wordlists = array(); // Wordlists to pick words from protected $_wordlists = array(); /* Public Methods */ public function setWordlists($wordlists = array()) {} public function setUsedWords($used_words = array()) {} public function setUsedWordlists($used_wordlists = array()) {} public function getRandomWord() {} // COUPLING POINT! Will most likely need to communicate with both the Wordlist and Word classes /* Protected Methods */ protected function _checkAvailableWordlists() {} // COUPLING POINT! Might need to check if wordlists are deleted etc. protected function _checkAvailableWords() {} // COUPLING POINT! Method needs to get all words in a wordlist from the Word class } Game class Game { protected $_session_id; // The ID of a game session which gets stored in the database along with game details protected $_game_info = array(); // Game instantiation public function __construct($user_id) { if (! $this->_session_id = $this->_gameExists($user_id)) { // New game } else { // Resume game } } // This is the method I tried to make flexible by using abstract classes etc. // Does it even belong in this class at all? public function checkWord($answer, $native_word, $translation) {} // This method checks the answer against the native word / translation word, depending on game mode public function getGameInfo() {} // Returns information about a game session, or creates it if it does not exist public function deleteSession($session_id) {} // Deletes a game session from the database // Methods dealing with game session information protected function _gameExists($user_id) {} protected function _getProgress($session_id) {} protected function _updateProgress($game_info = array()) {} } The Game /* CONTROLLER */ /* "Guess the word" page */ // User input $game_type = $_POST['game_type']; // Chosen with radio buttons etc. $wordlists = $_POST['wordlists']; // Chosen with checkboxes etc. // Starts a new game or resumes one from the database $game = new Game($_SESSION['user_id']); $game_info = $game->getGameInfo(); // Instantiates a new Wordpicker $wordpicker = new Wordpicker(); $wordpicker->setWordlists((isset($game_info['wordlists'])) ? $game_info['wordlists'] : $wordlists); $wordpicker->setUsedWordlists((isset($game_info['used_wordlists'])) ? $game_info['used_wordlists'] : NULL); $wordpicker->setUsedWords((isset($game_info['used_words'])) ? $game_info['used_words'] : NULL); // Fetches an available word if (! $word_id = $wordpicker->getRandomWord()) { // No more words left - game over! $game->deleteSession($game_info['id']); redirect(); } else { // Presents word details to the user $word = new Word(); $word_info = $word->getWordInfo($word_id); } The Bit to Finish /* CONTROLLER */ /* "Check the answer" page */ // ?????????????????? ( http://pastebin.com/cc6MtLTR ) Make sure you toggle the 'Layout Width' to the right for a better view. Thanks in advance. Questions To which extent should objects be loosely coupled? If object A needs info from object B, how is it supposed to get this without losing too much cohesion? As suggested in the comments, models should hold all business logic. However, as objects should be independent, where to glue them together? Should the model contain some sort of "index" or "client" area which connects the dots? Edit: So basically what I should do for a start is to make a new model which I can more easily call with oneliners such as $model->doAction(); // Lots of code in here which uses classes! How about the method for checking words? Should it be it's own object? I'm not sure where I should put it as it's pretty much part of the 'game'. But on another hand, I could just leave out the 'abstraction and OOPness' and make it a method of the 'client model' which will be encapsulated from the controller anyway. Very unsure about this.

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• KlipFolio

  A highly configurable RSS dashboard for monitoring an extensive array of information sources

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• String Conversion to Char for Java Game

  - by Jen

  Is there someone who could help me achieve the following points on this problems? I can't seem to get it. I tried using toCharArray and Scanner to achieve this, but it doesn't work, nor do I know how to make this things possible for my word game. :( · Get a popular name of person, place, verse, saying or event from the user. This may have a single or multiple words in it. · Create a copy of this string to an array where each letter is replaced with a hyphen (-) and each space is replaced with an underscore (_). Symbols and numbers will remain shown. · The program then asks a letter from the user. If the letter is in the inputted string, then it should be shown on the array at the same position it is shown in the string. Meaning, the letter replaces the hyphen (-) at the correct position of the array. · The program again prompts for a letter from the user and replaces the hyphen (-) of the array if it exists on the inputted string. This will be repeatedly done until such time each hyphen (-) is replaced with the correct letter. · If the user inputs an invalid letter, that is, a letter that does not exist on the inputted string, then the program should inform the user. If this happens 3 times while there is still at least one hyphen on the array, then the program should inform the user that he lost the game and showing him the whole correct string. · If the user completes the game, meaning, all hyphens have been replaced with the correct letters; then the program should congratulate the user for a job well done.

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• HTML5 Canvas A* Star Path finding

  - by Veyha

  I am trying to learn A* Star Path finding. Library I am using this - https://github.com/qiao/PathFinding.js But I am don't understand one thing how to do. I am need find path from player.x/player.y (player.x and player.y is both 0) to 10/10 This code return array of where I am need to move - var path = finder.findPath(player.x, player.y, 10, 10, grid); I am get array where I am need to move, but how to apply this array to my player.x and player.y? Array structure like - 0: 0 1: 0 length: 2, 0: 1 1: 0 length: 2, ... I am very sorry for my bad English language. Thanks.

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• Game State / Screen Management

  - by Ashylnn Mac

  What's the best way to handle game states / screens? My problem is this: PlayGameScreen adds a new InventoryGameScreen to the game during it's update. This immediately adds InventoryGameScreen to the array of GameScreens. That's throwing an exception when iterating over the array that the contents of the array have changed. Should I have two more arrays, like screensToBeAdded and screensToBeRemoved and do all the processing for them at the end of the game loop after drawing all the other screens?

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• Matrices: Arrays or separate member variables?

  - by bjz

  I'm teaching myself 3D maths and in the process building my own rudimentary engine (of sorts). I was wondering what would be the best way to structure my matrix class. There are a few options: Separate member variables: struct Mat4 { float m11, m12, m13, m14, m21, m22, m23, m24, m31, m32, m33, m34, m41, m42, m43, m44; // methods } A multi-dimensional array: struct Mat4 { float[4][4] m; // methods } An array of vectors struct Mat4 { Vec4[4] m; // methods } I'm guessing there would be positives and negatives to each. From 3D Math Primer for Graphics and Game Development, 2nd Edition p.155: Matrices use 1-based indices, so the first row and column are numbered 1. For example, a12 (read “a one two,” not “a twelve”) is the element in the first row, second column. Notice that this is different from programming languages such as C++ and Java, which use 0-based array indices. A matrix does not have a column 0 or row 0. This difference in indexing can cause some confusion if matrices are stored using an actual array data type. For this reason, it’s common for classes that store small, fixed size matrices of the type used for geometric purposes to give each element its own named member variable, such as float a11, instead of using the language’s native array support with something like float elem[3][3]. So that's one vote for method one. Is this really the accepted way to do things? It seems rather unwieldy if the only benefit would be sticking with the conventional math notation.

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• Validation and Error Generation when using the Data Mapper Pattern

  - by AndyPerlitch

  I am working on saving state of an object to a database using the data mapper pattern, but I am looking for suggestions/guidance on the validation and error message generation step (step 4 below). Here are the general steps as I see them for doing this: (1) The data mapper is used to get current info (assoc array) about the object in db: +=====================================================+ | person_id | name | favorite_color | age | +=====================================================+ | 1 | Andy | Green | 24 | +-----------------------------------------------------+ mapper returns associative array, eg. Person_Mapper::getPersonById($id) : $person_row = array( 'person_id' => 1, 'name' => 'Andy', 'favorite_color' => 'Green', 'age' => '24', ); (2) the Person object constructor takes this array as an argument, populating its fields. class Person { protected $person_id; protected $name; protected $favorite_color; protected $age; function __construct(array $person_row) { $this->person_id = $person_row['person_id']; $this->name = $person_row['name']; $this->favorite_color = $person_row['favorite_color']; $this->age = $person_row['age']; } // getters and setters... public function toArray() { return array( 'person_id' => $this->person_id, 'name' => $this->name, 'favorite_color' => $this->favorite_color, 'age' => $this->age, ); } } (3a) (GET request) Inputs of an HTML form that is used to change info about the person is populated using Person::getters <form> <input type="text" name="name" value="<?=$person->getName()?>" /> <input type="text" name="favorite_color" value="<?=$person->getFavColor()?>" /> <input type="text" name="age" value="<?=$person->getAge()?>" /> </form> (3b) (POST request) Person object is altered with the POST data using Person::setters $person->setName($_POST['name']); $person->setFavColor($_POST['favorite_color']); $person->setAge($_POST['age']); *(4) Validation and error message generation on a per-field basis - Should this take place in the person object or the person mapper object? - Should data be validated BEFORE being placed into fields of the person object? (5) Data mapper saves the person object (updates row in the database): $person_mapper->savePerson($person); // the savePerson method uses $person->toArray() // to get data in a more digestible format for the // db gateway used by person_mapper Any guidance, suggestions, criticism, or name-calling would be greatly appreciated.

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• PyGtk: Scrolllist with Entry, can I set an Id

  - by max246

  I have a scroll list on my window that I am going to insert 2 entry for each row, I am trying to understand how I can catch the entry that has been changed and update my array with this value. I will explain what is my code: I have an array that has 2 fields: Name and Description Each row has 2 entry, Name and Description When I am going to modify the row number 2 I want to update my object on my array: rows[1].name = XXX rows[1].description = YYY

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• what's the overhead when allocating objects/arrays in Java?

  - by Gnijuohz

  How many bytes an array occupies in Java? Assume It's a 64bit machine and also assume there are N elements in an array, so all these elements would take up 2*N, 4*N or 8*N bytes for different types of array. And a lecture in Coursera says that it would occupy 2*N+24, 4*N+24 or 8*N+24 bytes for a N element array and the 24 byte is called overhead, but didn't explain it. Also objects have overheads, which is 16 bytes. What exactly are these overheads? Also, do these overheads only exist in Java? How about C, C++ and Python?

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• OutOfBounds Exception when creating a PolygonShape using jbox2d

  - by B3nGr33ni3r

  So here's the deal, i'm parsing a file that contains the vertices for a polygon, that i want to create in box2d. I create a new PolygonShape() and then call .set() giving it a defined array of Vec, and that defined array's .length property. I expected this to work, since the documentation for jbox2d says this method takes a Vec array, and the count of Vec objects in that array. However, it errors out, and it seems to be unrelated to my code. The error i get is Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 8 at org.jbox2d.collision.shapes.PolygonShape.set(PolygonShape.java:174) and, upon looking at that line in the jbox2d svn repository, i still cannot figure out the issue. Any help is appreciated!

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• Is using build-in sorting considered cheating in practice tests?

  - by user10326

  I am using one of the practice online judges where a practice problem is asked and one submits the answer and gets back if it is accepted or not based on test inputs. My question is the following: In one of the practice tests, I needed to sort an array as part of the solution algorithm. If it matters the problem was: find 2 numbers in an array that add up to a specific target. As part of my algorithm I sorted the array, but to do that I used Java's quicksort and not implement sorting as part of the same method. To do that I had to do: java.util.Arrays.sort(array); Since I had to use the fully qualified name I am wondering if this is a kind of "cheating". (I mean perhaps an online judge does not expect this) Is it? In a formal interview (since these tests are practice for interview as I understand) would this be acceptable?

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• grep/search for multiple lines in a file.

  - by GSto

  Let's say I have a file with a long nested array, that's formatted like this: array( 'key1' => array( 'val1' => 'val', 'val2' => 'val', 'val3' => 'val', ), 'key2' => array( 'val1' => 'val', 'val2' => 'val', 'val3' => 'val', ), //etc... ); what I would like to do is have a way to grep/search a file, and by knowing key 1, get all the lines (the sub-array) it contains. is this possible?

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• Fastest way to check if two square 2D arrays are rotationally and reflectively distinct

  - by kustrle

  The best idea I have so far is to rotate first array by {0, 90, 180, 270} degrees and reflect it horizontally or/and vertically. We basically get 16 variations [1] of first array and compare them with second array. if none of them matches the two arrays are rotationally and reflectively distinct. I am wondering if there is more optimal solution than this brute-force approach? [1] 0deg, no reflection 0deg, reflect over x 0deg, reflect over y 0deg, reflect over x and y 90deg, no reflection ...

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• A Multiple Substring Search Class: CIVStringSet

  A string array class using MFC or STL that performs very fast multiple string searches

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• Convert NSData to primitive variable with ieee-754 or twos-complement ?

  - by William GILLARD

  Hi every one. I am new programmer in Obj-C and cocoa. Im a trying to write a framework which will be used to read a binary files (Flexible Image Transport System or FITS binary files, usually used by astronomers). The binary data, that I am interested to extract, can have various formats and I get its properties by reading the header of the FITS file. Up to now, I manage to create a class to store the content of the FITS file and to isolate the header into a NSString object and the binary data into a NSData object. I also manage to write method which allow me to extract the key values from the header that are very valuable to interpret the binary data. I am now trying to convert the NSData object into a primitive array (array of double, int, short ...). But, here, I get stuck and would appreciate any help. According to the documentation I have about the FITS file, I have 5 possibilities to interpret the binary data depending on the value of the BITPIX key: BITPIX value | Data represented 8 | Char or unsigned binary int 16 | 16-bit two's complement binary integer 32 | 32-bit two's complement binary integer 64 | 64-bit two's complement binary integer -32 | IEEE single precision floating-point -64 | IEEE double precision floating-point I already write the peace of code, shown bellow, to try to convert the NSData into a primitive array. // self reefer to my FITS class which contain a NSString object // with the content of the header and a NSData object with the binary data. -(void*) GetArray { switch (BITPIX) { case 8: return [self GetArrayOfUInt]; break; case 16: return [self GetArrayOfInt]; break; case 32: return [self GetArrayOfLongInt]; break; case 64: return [self GetArrayOfLongLong]; break; case -32: return [self GetArrayOfFloat]; break; case -64: return [self GetArrayOfDouble]; break; default: return NULL; } } // then I show you the method to convert the NSData into a primitive array. // I restrict my example to the case of 'double'. Code is similar for other methods // just change double by 'unsigned int' (BITPIX 8), 'short' (BITPIX 16) // 'int' (BITPIX 32) 'long lon' (BITPIX 64), 'float' (BITPIX -32). -(double*) GetArrayOfDouble { int Nelements=[self NPIXEL]; // Metod to extract, from the header // the number of element into the array NSLog(@"TOTAL NUMBER OF ELEMENTS [%i]\n",Nelements); //CREATE THE ARRAY double (*array)[Nelements]; // Get the total number of bits in the binary data int Nbit = abs(BITPIX)*GCOUNT*(PCOUNT + Nelements); // GCOUNT and PCOUNT are defined // into the header NSLog(@"TOTAL NUMBER OF BIT [%i]\n",Nbit); int i=0; //FILL THE ARRAY double Value; for(int bit=0; bit < Nbit; bit+=sizeof(double)) { [Img getBytes:&Value range:NSMakeRange(bit,sizeof(double))]; NSLog(@"[%i]:(%u)%.8G\n",i,bit,Value); (*array)[i]=Value; i++; } return (*array); } However, the value I print in the loop are very different from the expected values (compared using official FITS software). Therefore, I think that the Obj-C double does not use the IEEE-754 convention as well as the Obj-C int are not twos-complement. I am really not familiar with this two convention (IEEE and twos-complement) and would like to know how I can do this conversion with Obj-C. In advance many thanks for any help or information.

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• Explain the Peak and Flag Algorithm

  - by Isaac Levin

  EDIT Just was pointed that the requirements state peaks cannot be ends of Arrays. So I ran across this site http://codility.com/ Which gives you programming problems and gives you certificates if you can solve them in 2 hours. The very first question is one I have seen before, typically called the Peaks and Flags question. If you are not familiar A non-empty zero-indexed array A consisting of N integers is given. A peak is an array element which is larger than its neighbours. More precisely, it is an index P such that 0 < P < N - 1 and A[P - 1] < A[P] A[P + 1] . For example, the following array A: A[0] = 1 A[1] = 5 A[2] = 3 A[3] = 4 A[4] = 3 A[5] = 4 A[6] = 1 A[7] = 2 A[8] = 3 A[9] = 4 A[10] = 6 A[11] = 2 has exactly four peaks: elements 1, 3, 5 and 10. You are going on a trip to a range of mountains whose relative heights are represented by array A. You have to choose how many flags you should take with you. The goal is to set the maximum number of flags on the peaks, according to certain rules. Flags can only be set on peaks. What's more, if you take K flags, then the distance between any two flags should be greater than or equal to K. The distance between indices P and Q is the absolute value |P - Q|. For example, given the mountain range represented by array A, above, with N = 12, if you take: two flags, you can set them on peaks 1 and 5; three flags, you can set them on peaks 1, 5 and 10; four flags, you can set only three flags, on peaks 1, 5 and 10. You can therefore set a maximum of three flags in this case. Write a function that, given a non-empty zero-indexed array A of N integers, returns the maximum number of flags that can be set on the peaks of the array. For example, given the array above the function should return 3, as explained above. Assume that: N is an integer within the range [1..100,000]; each element of array A is an integer within the range [0..1,000,000,000]. Complexity: expected worst-case time complexity is O(N); expected worst-case space complexity is O(N), beyond input storage (not counting the storage required for input arguments). Elements of input arrays can be modified. So this makes sense, but I failed it using this code public int GetFlags(int[] A) { List<int> peakList = new List<int>(); for (int i = 0; i <= A.Length - 1; i++) { if ((A[i] > A[i + 1] && A[i] > A[i - 1])) { peakList.Add(i); } } List<int> flagList = new List<int>(); int distance = peakList.Count; flagList.Add(peakList[0]); for (int i = 1, j = 0, max = peakList.Count; i < max; i++) { if (Math.Abs(Convert.ToDecimal(peakList[j]) - Convert.ToDecimal(peakList[i])) >= distance) { flagList.Add(peakList[i]); j = i; } } return flagList.Count; } EDIT int[] A = new int[] { 7, 10, 4, 5, 7, 4, 6, 1, 4, 3, 3, 7 }; The correct answer is 3, but my application says 2 This I do not get, since there are 4 peaks (indices 1,4,6,8) and from that, you should be able to place a flag at 2 of the peaks (1 and 6) Am I missing something here? Obviously my assumption is that the beginning or end of an Array can be a peak, is this not the case? If this needs to go in Stack Exchange Programmers, I will move it, but thought dialog here would be helpful. EDIT

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• How to define an n-m relation in doctrine?

  - by murze

  If got a table "Article" and a table "Tags". Articles can have multiple tags and tags can hang to multiple articles. The class BaseArticle looks like this: abstract class BaseArticle extends Doctrine_Record { public function setTableDefinition() { $this->setTableName('article'); $this->hasColumn('article_id', 'integer', 8, array( 'type' => 'integer', 'length' => 8, 'fixed' => false, 'unsigned' => false, 'primary' => true, 'autoincrement' => true, )); $this->hasColumn('title', 'string', null, array( 'type' => 'string', 'fixed' => false, 'unsigned' => false, 'primary' => false, 'notnull' => false, 'autoincrement' => false, )); $this->hasColumn('text', 'string', null, array( 'type' => 'string', 'fixed' => false, 'unsigned' => false, 'primary' => false, 'notnull' => false, 'autoincrement' => false, $this->hasColumn('url', 'string', 255, array( 'type' => 'string', 'length' => 255, 'fixed' => false, 'unsigned' => false, 'primary' => false, 'notnull' => false, 'autoincrement' => false, )); } public function setUp() { parent::setUp(); $this->hasMany('Tag as Tags', array( 'local' => 'article_id', 'foreign'=>'tag_id', 'refClass'=>'Articletag') ); } } The BaseTag-class like this: abstract class BaseTag extends Doctrine_Record { public function setTableDefinition() { $this->setTableName('tag'); $this->hasColumn('tag_id', 'integer', 4, array( 'type' => 'integer', 'length' => 4, 'fixed' => false, 'unsigned' => false, 'primary' => true, 'autoincrement' => true, )); $this->hasColumn('name', 'string', null, array( 'type' => 'string', 'fixed' => false, 'unsigned' => false, 'primary' => false, 'notnull' => false, 'autoincrement' => false, )); } public function setUp() { parent::setUp(); $this->hasMany('Article as Articles', array( 'local' => 'tag_id', 'foreign'=>'article_id', 'refClass'=>'Articletag') ); } } And the relationship class like this: abstract class BaseArticletag extends Doctrine_Record { public function setTableDefinition() { $this->setTableName('articletag'); $this->hasColumn('article_id', 'integer', 8, array( 'type' => 'integer', 'length' => 8, 'fixed' => false, 'unsigned' => false, 'primary' => true, 'autoincrement' => false, )); $this->hasColumn('tag_id', 'integer', 4, array( 'type' => 'integer', 'length' => 4, 'fixed' => false, 'unsigned' => false, 'primary' => true, 'autoincrement' => false, )); } public function setUp() { parent::setUp(); } } When I try to get a property from the article all goes well by using: $article = Doctrine_Query::create()->from('Article a') ->where('id = ?' , 1) ->fetchOne(); echo $article->title; //gives me the title But when I try this: foreach($article->Tags as $tag) { echo($tag->name) } I get an error: Unknown record property / related component "Tags" on "Article"

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