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• What are some useful SQL statements that should be known by all developers who may touch the Back en

  - by Jian Lin

  What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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• Subtracting Delphi Time Ranges from a Date Range, Calculate Remaining Time

  - by Anagoge

  I'm looking for an algorithm that will help calculate a workday working time length. It would have an input date range and then allow subtracting partially or completely intersecting time range slices from that date range and the result would be the number of minutes (or the fraction/multiple of a day) left in the original date range, after subtracting out the various non-working time slices. For Example: Input date range: 1/4/2010 11:21 am - 1/5/2010 3:00 pm Subtract out any partially or completely intersecting slices like this: Remove all day Sunday Non-Sundays remove 11:00 - 12:00 Non-Sundays remove time after 5:00 pm Non-Sundays remove time before 8:00 am Non-Sundays remove time 9:15 - 9:30 am Output: # of minutes left in the input date range I don't need anything overly-general. I could hardcode the rules to simplify the code. If anyone knows of sample code or a library/function somewhere, or has some pseudo-code ideas, I'd love something to start with. I didn't see anything in DateUtils, for example. Even a basic function that calculates the number of minutes of overlap in two date ranges to subtract out would be a good start.

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• tomcat multithreading problem

  - by jutky

  Hi all I'm writing a java application that runs in Tomcat, on a multi-core hardware. The application executes an algorithm and returns the answer to the user. The problem is that even when I run two requests simultaneously, the tomcat process uses at most one CPU core. As far as I understand each request in Tomcat is executed in separate thread, and JVM should run each thread on separate CPU core. What could be the problem that bounds the JVM or Tomcat to use no more than one core? Thanks in advance.

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• Convert VB6 Randomize to C#

  - by Thomas G. Mayfield

  I'm writing a C# frontend to a legacy database that uses VB6 Rnd() and Randomize() methods for user password encryption. The encryption function is very simplistic and really not all that secure, but it's what all current passwords are stored with. What I'd like to be able to do is authenticate legacy users from a C# application. I can write new encryption (or preferably hashing) code for VB6 so that all future users have a more secure password, and that can be duplicated in C#. But I don't want to require current users to have had their password reset before they can use the new frontend. Is there any way I can reimplement that algorithm in C# so that it produces identical results to the legacy VB6 code?

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• List of divisors of an integer n (Haskell)

  - by Code-Guru

  I currently have the following function to get the divisors of an integer: -- All divisors of a number divisors :: Integer -> [Integer] divisors 1 = [1] divisors n = firstHalf ++ secondHalf where firstHalf = filter (divides n) (candidates n) secondHalf = filter (\d -> n `div` d /= d) (map (n `div`) (reverse firstHalf)) candidates n = takeWhile (\d -> d * d <= n) [1..n] I ended up adding the filter to secondHalf because a divisor was repeating when n is a square of a prime number. This seems like a very inefficient way to solve this problem. So I have two questions: How do I measure if this really is a bottle neck in my algorithm? And if it is, how do I go about finding a better way to avoid repetitions when n is a square of a prime?

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• Twitter oauth/request_token failing sometimes

  - by Techpriester

  Hello there. I'm implementing Twitters OAuth for Adobe AIR in Javascript. My problem is, that out of 100 requests to api.twitter.com/oauth/request_token about 30 fail with the usual error message: Failed to validate oauth signature and token The other 70% of requests produce a correct response, so I believe that my algorithm for signing is correct. I've read about invalid timestamps in a lot of forums and mailing lists but that is not the problem. My timestamps are correct. I also checked, if the nonces are unique, so that's not the cause either. Any ideas why this is happening?

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• java and mysql geting shortest path from to two points

  - by shaharnakash

  hi i have a mysql database that hold id ,name , oneid , twoid , size 1 1 1 2 4 2 2 1 3 1 3 3 2 1 74 4 4 2 4 2 5 5 2 5 12 6 6 4 2 12 7 7 4 6 74 8 8 4 7 12 9 9 3 5 32 10 10 3 8 22 11 11 5 3 66 12 12 5 6 76 13 13 5 9 33 14 14 6 10 11 15 15 6 7 21 16 16 8 3 12 17 17 8 9 10 18 18 9 8 2 19 19 9 10 72 20 20 10 6 31 21 21 10 7 7 22 22 10 9 18 23 23 7 6 8 i want to do Dijkstra algorithm but i cant get the details right if i got the contents to class Conn id ,name , oneid , twoid , size how do i find the path from oneid 1 to twoid 7 and believe me i triad many Dijkstra algorithms so please dont give me only reference

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• Reverse Breath First Search in C#

  - by Ngu Soon Hui

  Anyone has a ready implementation of the Reverse Breath First Search algorithm in C#? By Reverse Breath First Search, I mean instead of searching a tree starting from a common node, I want to search the tree from the bottom and gradually converged to a common node. Let's see the below figure, this is the output of a Breath First Search: In my reverse breath first search, 9,10,11 and 12 will be the first few nodes found ( the order of them are not important as they are all first order). 5, 6, 7 and 8 are the second few nodes found, and so on. 1 would be the last node found. Any ideas or pointers?

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• Strange problem when converting RGB to HSV

  - by zaplec

  Hi, I made a small RGB to HSV converter algorithm with C. It seems to work pretty well, but there is one strange problem: If I first convert i.e. a 800x600 picture into HSV map and then back to RGB map without doing any changes in the values, I get some pixels that are convertet incorrectly. Then if I try to convert those misbehaving single pixels alone to and back, they're converted correctly. Any idea what could be the problem? I'm using Daniel Karlings PNGLite to open that PNG file. Here are the source code of my main.c, rgbtohsv.c and rgbtohsv.h rgbToHsv.h rgbToHsv.c pngmain.c I linked pngmain only that if somebody wants to test and run this on his own system. -zaplec

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• Encryption-Decryption in Rails

  - by Salil

  Hi All, I am using require 'digest/sha1' to encrypt my password and save into database. During login I authenticate by matching the encrypted password saved in database and again encrypted the one use enter in password field. As of now everything works fine but now I want to do 'Forgot Password' functionality. To do this I need to decrypt the password which is saved in database to find original one. How to decrypt using digest/sha1? Or does anyone know any algorithm which supports encryption & decryption as well? I am using ruby on rails so I need Ruby way to accomplish it.

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• Breadth first search all paths

  - by Amndeep7

  First of all, thank you for looking at this question. For a school assignment we're supposed to create a BFS algorithm and use it to do various things. One of these things is that we're supposed to find all of the paths between the root and the goal nodes of a graph. I have no idea how to do this as I can't find a way to keep track of all of the alternate routes without also including copies/cycles. Here is my BFS code: def makePath(predecessors, last): return makePath(predecessors, predecessors[last]) + [last] if last else [] def BFS1b(node, goal): Q = [node] predecessor = {node:None} while Q: current = Q.pop(0) if current[0] == goal: return makePath(predecessor, goal) for subnode in graph[current[0]][2:]: if subnode[0] not in predecessor: predecessor[subnode[0]] = current[0] Q.append(subnode[0]) A conceptual push in the right direction would be greatly appreciated. tl;dr How do I use BFS to find all of the paths between two nodes?

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• Set NTFS Permissions with DirectorySecurity after created Active Dirctory Groups c#

  - by maverick

  Hi I am a little confused about setting NTFS Permissions to a directory after I created Active Directory Groups (both programmatically). When I created the Active Directory Objects then I have to wait a few seconds to set the NTFS Permissions. If I have not this timeout then I get sometimes an error message that the identify (active directory groupname) could not found. Is it possible that the DirectorySecurity-Class from DirectoryInfo-Class has an different algorithm to get the idenfity from active directory objects? Because when I checking the existing of the groups in active directory with System.DirectoryServices all the objects exist suddenly after creation. Kind regards

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• What are some useful SQL statements / usage patterns that should be known by all developers who may

  - by Jian Lin

  What are some useful SQL statements that should be known by all developers who may touch the Back end side of the project? (Update: just like in algorithm, we know there are sorting problems, shuffling problems, and we know some solutions to them. This question is aiming at the same thing). For example, ones I can think of are: Get a list of Employees and their boss. Or one with the employee's salary greater than the boss. (Self-join) Get a list of the most popular Classes registered by students, from the greatest number to the smallest. (Count, group by, order by) Get a list of Classes that are not registered by any students. (Outer join and check whether the match is NULL, or by Get from Classes table, all ClassIDs which are NOT IN (a subquery to get all ClassIDs from the Registrations table)) Are there some SQL statements that should be under the sleeve of all developers that might touch back end data?

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• File management

  - by user343934

  I am working on python and biopython right now. I have a file upload form and whatever file is uploaded suppose(abc.fasta) then i want to pass same name in execute (abc.fasta) function parameter and display function parameter (abc.aln). Right now i am changing file name manually, but i want to have it automatically. Workflow goes like this. ----If submit is not true then display only header and form part --- if submit is true then call execute() and get file name from form input --- Then display the save file result in the same page. File name is same as input. My raw code is here -- http://pastebin.com/FPUgZSSe Any suggestions, changes and algorithm is appreciated Thanks

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• Collision detection by sliding against a plane in XNA

  - by Bevin

  Hello, I am attempting to engineer a collision detection algorithm for a custom Minecraft client I'm making. Basically, the entire world is made up of cubes, and the player (or camera) needs to be able to stand on and move against these cubes. The result I want is illustrated in this image: The green line is the player's movement vector. When the player is brushing up against a plane of one of the cubes, I want the vector to change to one that is perpendicular with the plane. The vector should, however, keep all of it's velocity in the plane's direction, yet lose all velocity towards the plane. I hope I've made my question clear. What is the best and most efficient way to implement a collision detection system like this? Also, will a system like this allow for a simple gravity component?

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• smallest perimiter rectangle with given integer area and integer sides

  - by remuladgryta

  Given an integer area A, how can one find integer sides w and h of a rectangle such that w*h = A and w+h is as small as possible? I'd rather the algorithm be simple than efficient (although within reasonable efficiency). What would be the best way to accomplish this? Finding out the prime factors of A, then combining them in some way that tries to balance w and h? Finding the two squares with integer sides with areas closest to A and then somehow interpolating between them? Any other method i'm not thinking of?

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• How can I tell if a closed path contains a given point?

  - by Tom Seago

  In Android, I have a Path object which I happen to know defines a closed path, and I need to figure out if a given point is contained within the path. What I was hoping for was something along the lines of path.contains(int x, int y) but that doesn't seem to exist. The specific reason I'm looking for this is because I have a collection of shapes on screen defined as paths, and I want to figure out which one the user clicked on. If there is a better way to be approaching this such as using different UI elements rather than doing it "the hard way" myself, I'm open to suggestions. I'm open to writing an algorithm myself if I have to, but that means different research I guess.

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• How to detect identical part(s) inside string?

  - by Horace Ho

  I try to break down the http://stackoverflow.com/questions/2711961/decoding-algorithm-wanted question into smaller questions. This is Part I. Question: two strings: s1 and s2 part of s1 is identical to part of s2 space is separator how to extract the identical part(s)? example 1: s1 = "12 November 2010 - 1 visitor" s2 = "6 July 2010 - 100 visitors" the identical parts are "2010", "-", "1" and "visitor" example 2: s1 = "Welcome, John!" s2 = "Welcome, Peter!" the identical parts are "Welcome," and "!" Python and Ruby preferred. Thanks

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• Sorting a list of variable length integers delimited by decimal points...

  - by brewerdc

  Hey guys, I'm in need of some help. I have a list of delimited integer values that I need to sort. An example: Typical (alpha?) sort: 1.1.32.22 11.2.4 2.1.3.4 2.11.23.1.2 2.3.7 3.12.3.5 Correct (numerical) sort: 1.1.32.22 2.1.3.4 2.3.7 2.11.23.1.2 3.12.3.5 11.2.4 I'm having trouble figuring out how to setup the algorithm to do such a sort with n number of decimal delimiters and m number of integer fields. Any ideas? This has to have been done before. Let me know if you need more information. Thanks a bunch! -Daniel

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• [Ruby] How can I randomly iterate through a large Range?

  - by void

  I would like to randomly iterate through a range. Each value will be visited only once and all values will eventually be visited. For example: (0..9).sort_by{rand}.map{|x| f(x)} where f(x) is some function that operates on each value. A Fisher-Yates shuffle could be used to increase efficiency, but this code is sufficient for many purposes. My problem is that sort_by will transform the range into an array, which is not cool because I am working with astronomically large numbers. Ruby will quickly consume a large amount of RAM trying to create a monstrous array. This is also why the following code will not work: tried = {} # store previous attempts bigint = 99**99 bigint.times { x = rand(bigint) redo if tried[x] tried[x] = true f(x) # some function } This code is very naive and quickly runs out of memory as tried obtains more entries. What sort of algorithm can accomplish what I am trying to do?

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• Is it possible to manipulate the format on a DataGridView that is bound to a Data Source?

  - by Jack Johnstone

  I´m using SQL Server 2005 and Visual Studio 2008, C#. In the data source (the SQL Server data table) I use the date format mm/dd/yyyy, however, in a forms overview (DataGridView) users would like to see a completely other format, with year, week number and day number of week (yyww,d). I´ve created an algorithm for this transformation, but can I populate the affected cells with yyww,d instead of mm/dd/yyyy? And in that case - how would I do it? I guess I need to do it after the cells are populated, but before they are shown. The generic question is - how do I manipulate the format of Data Source bound DataGridView cells.

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• Whats the deal with python?

  - by gmatt

  My interests in programming lie mainly in algorithms, and lately I have seen many reputable researchers write a lot of their code in python. How easy and convenient is python for scientific computing? Does it have a library of algorithms that compares to matlab's? Is Python a scripting language or does it compile? Is it a great language for prototyping an algorithm? How long would it take me to learn enough of it to be productive provided I know C well and OO programming somewhat? Is it OO based? Sorry for the condensed format of questions, but I'm very curious and was hoping a more experienced programmer could help me out.

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• Standardizing camera input in OpenCV? (Contrast/Saturation/Brightness etc..)

  - by karpathy

  I am building an application using OpenCV that uses the webcam and runs some vision algorithms. I would like to make this application available on the internet after I am done, but I am concerned about the vast differences in camera settings on every computer, and I am worried that the algorithm may break if the settings are too different from mine. Is there any way, after capturing the frame, to post process it and make sure that the contrast is X, brightness is Y, and saturation is Z? I think the Camera settings themselves can not be changed from code directly using the current OpenCV Python bindings. Would anyone be able to tell me about how I could calculate some of these parameters from the image and adjust them appropriately using OpenCV?

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• Determining whether a file is a duplicate

  - by Todd R

  Is there a reliable way to determine whether or not two files are the same? For example, two files with the same size and type may or may not be the same binarilly (yeah, I know it's not really a word). I assume that comparing one or two checksums of the files will help, but I wonder: How reliable are checksums at determining whether two files are different; what are the chances of two different files having the same checksum? Would reliability increase by applying additional checksum comparisons? Which checksum algorithm(s) would be the most efficient and/or reliable? Any ideas, suggestions or thoughts are appreciated! P.S. The code for this is being written in Java running on a nix system, but generic or platform agnostic input is most helpful.

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• I'm having a problem identifying a floating point exception.

  - by Peter Stewart

  I'm using c++ in visual studio express to generate random expression trees for use in a genetic algorithm type of program. Because they are random, the trees often generate (I'll call them exceptions, I'm not sure what they are) Thanks to a suggestion by George, I turned the mask _MCW_EM on so that hardware interrupts are turned off. (the default) So, the program runs uninterrupted, but some of the values returned are: -1.#INF, -1.#NAN, -1.#INV. I don't know how to identify these so that I can throw an exeption: if ( variable == -1.#INF) ?? DigitalRoss in this post seemed to have the solution, but as I understood it I couldn't make it work. I've been looking all over the place for this simple bit of code, that I assumed would be used all the time, but have had no luck. thanks

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