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• What is a Coding Dojo?

  - by huwyss

  Recently i found out that there is a thing called "coding dojo". The point behind it is that software developers want to have a space to learn new stuff like processes, methods, coding details, languages, and whatnot in an environment without stress. Just for fun. No competition. No results required. No deadlines.Some days ago I joined the Zurich coding dojo. We were three programmers with different backgrounds.We gave ourselves the task to develop a method that takes an input value and returns its prime factors. We did pair programming and every few minutes we switched positions. We used test driven development. The chosen programming language was Ruby.I haven't really done TDD before. It was pretty interesting to see the algorithm develop following the testcases.We started with the first test input=1 then developed the most simple productive program that passed this very first test. Then we added the next test input=2 and implemented the productive code. We kept adding tests and made sure all tests are passed until we had the general solution.When we improved the performance of our code we saw the value of the tests we wrote before. Of course our first performance improvement broke several tests.It was a very interesting experience to see how other developers think and how they work. I will participate at the dojo again and can warmly recommend it to anyone. There are  coding dojos all over the world.Have fun!

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• Using template questions in a technical interview

  - by Desolate Planet

  I've recently been in an argument with a colleague about technical questions in interviews. As a graduate, I went round lots of companies and noticed they used the same questions. An example is "Can you write a function that determines if a number is prime or not?", 4 years later, I find that particular question is quite common even for a junior developer. I might not be looking at this the correct way, but shouldn't software houses be intelligent enough to think up their own interview questions? I've been to about 16 interviews as a graduate and the same questions came up in about 75% of them. This leads me to believe that many companies are lazy and simply Google: 'Template questions for interviewing software developers' and I look down on that. Question: Is it better to use a set of questions off some template or should software houses strive to be more original and come up with their own interview material? From my point of view, if I failed an interview and went off and looked for good answers to the questions I messed up on, I could fly through the next interview if the questions are the same.

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• Finding maximum number of congruent numbers

  - by Stefan Czarnecki

  Let's say we have a multiset (set with possible duplicates) of integers. We would like to find the size of the largest subset of the multiset such that all numbers in the subset are congruent to each other modulo some m 1. For example: 1 4 7 7 8 10 for m = 2 the subsets are: (1, 7, 7) and (4, 8, 10), both having size 3. for m = 3 the subsets are: (1, 4, 7, 7, 10) and (8), the larger set of size 5. for m = 4 the subsets are: (1), (4, 8), (7, 7), (10), the largest set of size 2. At this moment it is evident that the best answer is 5 for m = 3. Given m we can find the size of the largest subset in linear time. Because the answer is always equal or larger than half of the size of the set, it is enough to check for values of m upto median of the set. Also I noticed it is necessary to check for only prime values of m. However if values in the set are large the algorithm is still rather slow. Does anyone have any ideas how to improve it?

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• get me the latest Change from Select Query in below given condition

  - by OM The Eternity

  I have a Table structure as id, trackid, table_name, operation, oldvalue, newvalue, field, changedonetime Now if I have 3 rows for the same "trackid" same "field", then how can i select the latest out of the three? i.e. for e.g.: id = 100 trackid = 152 table_name = jos_menu operation= UPDATE oldvalue = IPL newvalue = IPLcccc field = name live = 0 changedonetime = 2010-04-30 17:54:39 and id = 101 trackid = 152 table_name = jos_menu operation= UPDATE oldvalue = IPLcccc newvalue = IPL2222 field = name live = 0 changedonetime = 2010-04-30 18:54:39 As u can see above the secind entry is the latest change, Now what query I should use to get the only one and Latest row out of many such rows... $distupdqry = "select DISTINCT trackid,table_name from jos_audittrail where live = 0 AND operation = 'UPDATE'"; $disupdsel = mysql_query($distupdqry); $t_ids = array(); $t_table = array(); while($row3 = mysql_fetch_array($disupdsel)) { $t_ids[] = $row3['trackid']; $t_table[] = $row3['table_name']; //$t_table[] = $row3['table_name']; } //echo "<pre>";print_r($t_table);echo "<pre>"; //exit; for($n=0;$n<count($t_ids);$n++) { $qupd = "SELECT * FROM jos_audittrail WHERE operation = 'UPDATE' AND trackid=$t_ids[$n] order by changedone DESC "; $seletupdaudit = mysql_query($qupd); $row4 = array(); $audit3 = array(); while($row4 = mysql_fetch_array($seletupdaudit)) { $audit3[] = $row4; } $updatefield = ''; for($j=0;$j<count($audit3);$j++) { if($j == 0) { if($audit3[$j]['operation'] == "UPDATE") { //$insqry .= $audit2[$i]['operation']." "; //echo "<br>"; $updatefield .= "UPDATE `".$audit3[$j]['table_name']."` SET "; } } if($audit3[$j]['operation'] == "UPDATE") { $updatefield .= $audit3[$j]['field']." = '".$audit3[$j]['newvalue']."', "; } } /*echo "<pre>"; print_r($audit3); exit;*/ $primarykey = "SHOW INDEXES FROM `".$t_table[$n]."` WHERE Key_name = 'PRIMARY'"; $prime = mysql_query($primarykey); $pkey = mysql_fetch_array($prime); $updatefield .= "]"; echo $updatefield = str_replace(", ]"," WHERE ".$pkey['Column_name']." = '".$t_ids[$n]."'",$updatefield); } In the above code I am fetching ou the distinct IDs in which update operation has been done, and then accordingly query is fired to get all the changes done on different fields of the selected distinct ids... Here I am creating the Update query by fetching the records from the initially described table which is here mentioned as audittrail table... Therefore I need the last made change in the field so that only latest change can be selected in the select queries i have used... please go through the code.. and see how can i make the required change i need finally..

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• Is git / tortoisegit ready to replace snv / tortoisesvn on windows?

  - by opensas

  I've been using svn thru tortoise and svn:// protocol on windows for a couple of years and I'm pretty comfortable with it. Nevertheless tThere are a couple of features I'd like to hove, mainly shelves (something like local commits) and easier branch / merge support. From my experience, svn / tortoise on windows is rock solid stuff. I was wondering if git / tortoisegit has achieved the level of maturity and stability so as to be a replacement for svn on windows. Any experience about it? saludos sas some links: a similar question, only a bit outdated http://stackoverflow.com/questions/1500400/is-tortoisegit-ready-for-prime-time-yet http://stackoverflow.com/questions/931105/tortoisegit-tortoisebzr-tortoisehg-are-any-solid-enough-to-switch-from-tortois (well, it seems like mercurial could be an option) http://code.google.com/p/tortoisegit/ http://www.syntevo.com/smartgit/index.html (free of charge for non-commercial use or to active members of the Open Source community)

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• log4j floods my console

  - by srikanth VM

  This is the log4j.properties that i have in my app log4j.rootLogger=B C log4j.logger.A=INFO, A1 log4j.debug=false log4j.appender.A1=org.apache.log4j.ConsoleAppender log4j.appender.A1.layout=org.apache.log4j.PatternLayout log4j.appender.A1.layout.ConversionPattern=%d [%t] %-5p %C - %m%n log4j.logger.B=INFO, A2 log4j.debug=false log4j.appender.A2=org.apache.log4j.FileAppender log4j.appender.A2.file=PRIME-log.txt log4j.appender.A2.layout=org.apache.log4j.PatternLayout log4j.appender.A2.layout.ConversionPattern=%d [%t] %-5p %C - %m%n log4j.logger.C=INFO, A3 log4j.appender.A3=org.apache.log4j.FileAppender log4j.appender.A3.file=employee_pass_regeneration-log.txt log4j.appender.A3.layout=org.apache.log4j.PatternLayout log4j.appender.A3.layout.ConversionPattern=%d [%t] %-5p %C - %m%n I only want File appender so i only use that , but some how my console is always flooded with DEBUG messages which i have never used 8704 [http-8080-2] DEBUG org.springframework.web.servlet.view.JstlView - Rendering view with name 'passIndex' with model null and static attributes {} I guess these are all system messages , but with these debug messages its really hard to debug actually i mean i cannot find my own sysouts i tried log4j.debug=false but still i get these messages

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• Time complexity of Sieve of Eratosthenes algorithm

  - by eSKay

  From Wikipedia: The complexity of the algorithm is O(n(logn)(loglogn)) bit operations. How do you arrive at that? That the complexity includes the loglogn term tells me that there is a sqrt(n) somewhere. Suppose I am running the sieve on the first 100 numbers (n = 100), assuming that marking the numbers as composite takes constant time (array implementation), the number of times we use mark_composite() would be something like n/2 + n/3 + n/5 + n/7 + ... + n/97 = O(n) And to find the next prime number (for example to jump to 7 after crossing out all the numbers that are multiples of 5), the number of operations would be O(n). So, the complexity would be O(n^2). Do you agree?

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• Getting into a technology which requires experience when you have no experience

  - by dotnetdev

  It seems that Sharepoint is a technology which is very hard to get into. All the jobs in this tech require experience in working with it (Eg 2 years development experience in MOSS). If I wanted to get into this - but had no job that used the tech, how can I get experience in it to get an experienced job? Jobs state you need "2 years professional experience in MOSS 2007" but then if you have never done it, you won't get the job. The only possible way is you will be doing this at home and not in a team, but if you work in the mean time, that will negate this (it's not like teamworking is tech specific). Many people think if you decide to make a project at home you're just going to play about aimlessly rather than work to specs (where as in my current situation it's vice versa) but if you're dedicated, like me, you would write them - just not with the same presentation. Would employers treat experience at home as professional experience? Biztalk is another prime example of this. Thanks

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• Uninstall Mono from Mac OS X v10.5 Leopard

  - by Mac

  I installed Mono on my iMac last night and I immidiately had a change of heart! I don't think Mono is ready for prime time. The Mono website says to run the following script to uninstall: #!/bin/sh -x #This script removes Mono from an OS X System. It must be run as root rm -r /Library/Frameworks/Mono.framework rm -r /Library/Receipts/MonoFramework-SVN.pkg cd /usr/bin for i in `ls -al | grep Mono | awk '{print $9}'`; do rm ${i} done Has anyone had to uninstall Mono? Was it as straight forward as running the above script or do I have to do more? How messy was it? Any pointers are appreciated. Thanks

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• using AudioQueues with AudioFileReadBytes

  - by Santosh

  Hey Im trying to work with Audio queues to play a very big mp3 file (arround 23 hours long). when audio queue asks for buffers though callback, im using AudioFileReadBytes() API to read the bytes from audio file and feed the queue. startQueue fails with the error : prime failed any inputs????? Also I succeeded playing file using AudioFileReadPackets API instead of AudioFileReadBytes(). But the problem with API is that when I seek (fast forward) by a long interval, say 9 hours (for example fast forward from 32 mins playtime to 9:32 mins) then AudioFileReadPackets() takes a long time (almost 2 mins) to read from new location. any comments would be greatly appreciated.

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• Recognizing when to use the mod operator

  - by Will

  I have a quick question about the mod operator. I know what it does; it calculates the remainder of a division. My question is, how can I identify a situation where I would need to use the mod operator? I know I can use the mod operator to see whether a number is even or odd and prime or composite, but that's about it. I don't often think in terms of remainders. I'm sure the mod operator is useful and I would like to learn to take advantage of it. I just have problems identifying where the mod operator is applicable. In various programming situations, it is difficult for me to see a problem and realize "hey! the remainder of division would work here!" Any tips or strategies? Thanks

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• What are the preferred versions of Vim and Emacs on Mac OS X?

  - by Michiel de Mare

  For those of us that like to use the graphical version of Vim or Emacs, instead of the console version, which version do you recommend? For Vim, there's Mac OS X Vim, MacVim, Vim-Cocoa. For Emacs, CarbonEmacs, XEmacs, and Aquamacs. Are there more? Which of these are ready for prime-time? If it's a tough call, what are the trade-offs? Are all of these still being maintained? No discussion of Vim vs. Emacs, if you don't mind, or comparisons with other editors.

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• No speed-up with useless printf's using OpenMP

  - by t2k32316

  I just wrote my first OpenMP program that parallelizes a simple for loop. I ran the code on my dual core machine and saw some speed up when going from 1 thread to 2 threads. However, I ran the same code on a school linux server and saw no speed-up. After trying different things, I finally realized that removing some useless printf statements caused the code to have significant speed-up. Below is the main part of the code that I parallelized: #pragma omp parallel for private(i) for(i = 2; i <= n; i++) { printf("useless statement"); prime[i-2] = is_prime(i); } I guess that the implementation of printf has significant overhead that OpenMP must be duplicating with each thread. What causes this overhead and why can OpenMP not overcome it?

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• The Community-Driven GDB Primer

  - by fbrereto

  I was reading this question and realized it might be helpful for entry- and pro-level developers alike (including myself) to have a common reference for best practices in using gdb. Many questions asked on Stack Overflow could easily be solved by taking some time to step some code in a debugger, and it would be good to have a community-approved resource to "teach them how to fish", so to speak. Even for those seasoned veterans who occasionally find themselves in gdb when they are accustomed to a GUI-tastic debugger might benefit from those who are much more familiar with the command line tool. For starters (both to gdb and to prime this thread) I submit: Ninefinger's gdb primer The gdb quick reference guide, which is useful for telling you what commands are available but not how best to use them. My hope is this thread is a seed planted that is of continued value to the community. If by "continued value" the community decides to nix it altogether, well then the masses have spoken.

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• Modifying an old Windows program not to call exit after a keypress without source access

  - by rustyn2

  I have an older C++ Windows program that I've been asked to get run in a kiosk style environment for a student project. From the main menu, hitting ESC will exit the program, which is undesirable. In ye olden days I would have trapped the keyboard interrupt or whatever and dug around to NOOP whatever JMP or CALL was getting referenced in the case statement that likely decides all that, but on Windows everything goes through various registered event handlers, and I haven't done any windows internals work in about 10 years. Is there a good tool to breakpoint a program on certain WM_EVENT (WM_KEYDOWN being a prime target) messages or similar, so that I can narrow down where in the executable the check is made? I'm currently stepping back from various potential system calls made before the various thread cleanups and final exit calls but it seems like there has to be a better way to do this that I'm forgetting.

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• Pohlig–Hellman algorithm for computing discrete logarithms

  - by drelihan

  Hi Folks, I'm working on coding the Pohlig-Hellman Algorithm but I am having problem understand the steps in the algorithm based on the definition of the algorithm. Going by the Wiki of the algorithm: http://en.wikipedia.org/wiki/Pohlig%E2%80%93Hellman_algorithm I know the first part 1) is to calculate the prime factor of p-1 - which is fine. Howeever, I am not sure what I need to do in steps 2) and 3). Can someone help with explaining this in plain english (i) - or pseudocode. I want to code the solution myself obviously but I cannot make any more progress unless i understand the algorithm. Note: I have done a lot of searching for this and I read S. Pohlig and M. Hellman (1978). "An Improved Algorithm for Computing Logarithms over GF(p) and its Cryptographic Significance but its still not really making sense to me. Thanks in advance

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• Why are primes important in cryptography?

  - by Michael Stum

  One thing that always strikes me as a non-cryptographer: Why is it so important to use Prime numbers? What makes them so special in cryptography? Does anyone have a simple short explanation? (I am aware that there are many primers and that Applied Cryptography is the Bible, but as said: I am not looking to implement my own cryptographic algorithm, and the stuff that I found just made my brain explode - no 10 pages of math formulas please :)) Thanks for all the answers. I've accepted the one that made the actual concept most clear to me.

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• Most optimized way to calculate modulus in C

  - by hasanatkazmi

  I have minimize cost of calculating modulus in C. say I have a number x and n is the number which will divide x when n == 65536 (which happens to be 2^16): mod = x % n (11 assembly instructions as produced by GCC) or mod = x & 0xffff which is equal to mod = x & 65535 (4 assembly instructions) so, GCC doesn't optimize it to this extent. In my case n is not x^(int) but is largest prime less than 2^16 which is 65521 as I showed for n == 2^16, bit-wise operations can optimize the computation. What bit-wise operations can I preform when n == 65521 to calculate modulus.

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• Selection of parameters in Diffie-Hellman

  - by allenzzzxd

  Hello, maybe it's not so proper to ask this question here... anyway, I'm trying to use the gmp library for the implementation of DH, but the problem here I got is: Once, when I was doing the tests to observe the output, although big values of prime and the private keys were selected: p was about more than 300 digits long in decimal a, b were about 100 digits long finally I got a shared secret key which was extremely small, perhaps smaller than 10^8 in decimal... This problem didn't show up many times, in fact, during all the observation, it appeared just once...but still, this was not so good at all. So I wonder if there are some methods which can avoid this... Thanx a lot

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• MAD method compression function

  - by Jacques

  I ran across the question below in an old exam. My answers just feels a bit short and inadequate. Any extra ideas I can look into or reasons I have overlooked would be great. Thanx Consider the MAD method compression function, mapping an object with hash code i to element [(3i + 7)mod9027]mod6000 of the 6000-element bucket array. Explain why this is a poor choice of compression function, and how it could be improved. I basically just say that the function could be improved by changing the value for p (or 9027) to an prime number and choosing an other constant for a (or 3) could also help.

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• What challenges are there in making an iPhone IDE for Windows/Linux?

  - by Moshe

  First of all, is this possible? If so: What challenges would I encounter in making an XCode imitation for iPhone/iPod development for Windows or Linux? I was thinking about using gcc as the actual compiler for the objecitve-c. Will that work? It doesn't need to compile to iPhone OS until it is to be tested on the device or submitted to the app store. Perhaps it will be easier to compile to the local OS format (Windows or Linux) until "prime-time".

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• Self updating application install with WIX?

  - by Brian ONeil

  I am writing an application that needs to be installed on a large number of desktops and also needs to update itself. We are looking at WIX for creating the installation. I have used ClickOnce and it is not a good solution for this install. WIX seems to fit, but there is no good process for auto update that I have found. I have looked at ClickThrough, but it doesn't seem ready for prime time yet. Does anyone have another good solution to use with WIX (or maybe another install program) to auto update an application install?

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• Interesting interview question. .Net

  - by rahul

  Coding Problem NumTrans There is an integer K. You are allowed to add to K any of its divisors not equal to 1and K. The same operation can be applied to the resulting number and so on. Notice that starting from the number 4, we can reach any composite number by applying several such operations. For example, the number 24 can be reached starting from 4 using 5 operations: 468121824 You will solve a more general problem. Given integers n and m, return the minimal number of the described operations necessary to transform n into m. Return -1 if m can't be obtained from n. Definition Method signature: int GetLeastCount (int n, int m) Constraints N will be between 4 and 100000, inclusive. M will be between N and 100000, inclusive. Examples 1) 4 576 Returns: 14 The shortest order of operations is: 468121827365481108162243324432576 2) 8748 83462 Returns: 10 The shortest order of operations is: 874813122196832624439366590497873283106834488346083462 3) 4 99991 Returns: -1 The number 99991 can't be obtained because it’s prime!

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• Active Record/ORM vs Normal Forms?

  - by Arsenal

  Hello, I've been playing around with Active Record a bit, and I have noticed that A.C./ORM always uses the following database model when creating a one-to-one relationship Person id | country_id | name | ... Country id | tld | name | ... No I wondered, isn't this a violiation of the third Normal Form? This clearly states "Every non-prime attribute is non-transitively dependent on every key of the table". Well this country_id isn't dependent of personid is it? So is this wrong or am I just not getting the point?

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• Matlab code help. Backward Euler method.

  - by m0s

  Here is the matlab/freemat code I got to solve ODE numerically using backward Euler method. However the results are inconsistent with my textbook results, and sometimes even ridiculously inconsistent. Please point out what is wrong with the code. I have already asked this question on mathoverflow.com no help there, hope someone here can help. function [x,y]=backEuler(f,xinit,yinit,xfinal,h) %f - this is your y prime %xinit - initial X %yinit - initial Y %xfinal - final X %h - step size n=(xfinal-xinit)/h; %Calculate steps %Inititialize arrays... %1st elements take xinit and yinit corespondigly, the rest fill with 0s x=[xinit zeros(1,n)]; y=[yinit zeros(1,n)]; %Numeric routine for i=1:n x(i+1)=x(i)+h; ynew=y(i)+h*(f(x(i),y(i))); y(i+1)=y(i)+h*f(x(i+1),ynew); end end

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