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• Pointer incrementing query

  - by Craig

  I have been looking at this piece of code, and it is not doing what I expect. I have 3 globals. int x, y, *pointer, z; Inside of main I declare them. x = 10; y = 25; pointer = &x; now at this point &x is 0x004A144 &y is 0x004A138 pointer is pointing to 0x004A144 Now when I increment: y = *++pointer; it points to 0x004A148, this is the address y should be at shouldn't it? The idea is that incrementing the pointer to 'x' should increment it to point at y, but it doesn't seem to want to declare them in in order like I expect. If this a VS2005 / 2008 problem? Or maybe an Express problem? This isn't really homework, as I have done it a couple of years ago but I was revising on my pointer stuff and I tried this again. But this time I am getting unexpected results. Does anyone have opinions on this? *UPDATE sorry should be more clear, 'thought' on declaration 'y' should be at 148, and that incrementing the pointer pointing to x should increment 'pointer' to 148 (which it does), but that isn't where y is. Why isn't y declaring where it should be.

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• Java semaphore to syncronize printing to screen

  - by Travis Griswald

  I'm currently stuck on a bit of homework and was wondering if anyone could help - I have to use semaphores in java to syncronize printing letters from 2 threads - one printing "A" and one printing "B". I cannot print out more than 2 of the same character in a row, so output should look like AABABABABABBABABABABAABBAABBABABA At the moment I have 3 semaphores, a binary mutex set to 1, and a counting semaphore, and my thread classes look something like this - public void run() { while (true) { Time.delay(RandomGenerator.integer(0,20)); Semaphores.mutex.down (); System.out.println (produce()); if (printCount > 1) { printCount = 0; Semaphores.mutex.up (); Semaphores.printB.up(); } } } public String produce() { printCount++; return "A"; } public void run() { while (true) { Time.delay(RandomGenerator.integer(0,20)); Semaphores.mutex.down (); System.out.println (produce()); if (printCount > 1) { printCount = 0; Semaphores.mutex.up (); Semaphores.printA.up(); } } } public String produce() { printCount++; return "B"; } Yet whatever I try it either deadlocks, or it seems to be working only printing 2 in a row at most, but always seems to print 3 in a row every now and again! Any help is much appreciated, not looking code or anything just a few pointers if possible :)

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• Which is the better C# class design for dealing with read+write versus readonly

  - by DanM

  I'm contemplating two different class designs for handling a situation where some repositories are read-only while others are read-write. (I don't foresee any need to a write-only repository.) Class Design 1 -- provide all functionality in a base class, then expose applicable functionality publicly in sub classes public abstract class RepositoryBase { protected virtual void SelectBase() { // implementation... } protected virtual void InsertBase() { // implementation... } protected virtual void UpdateBase() { // implementation... } protected virtual void DeleteBase() { // implementation... } } public class ReadOnlyRepository : RepositoryBase { public void Select() { SelectBase(); } } public class ReadWriteRepository : RepositoryBase { public void Select() { SelectBase(); } public void Insert() { InsertBase(); } public void Update() { UpdateBase(); } public void Delete() { DeleteBase(); } } Class Design 2 - read-write class inherits from read-only class public class ReadOnlyRepository { public void Select() { // implementation... } } public class ReadWriteRepository : ReadOnlyRepository { public void Insert() { // implementation... } public void Update() { // implementation... } public void Delete() { // implementation... } } Is one of these designs clearly stronger than the other? If so, which one and why? P.S. If this sounds like a homework question, it's not, but feel free to use it as one if you want :)

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• String Manipulation in C

  - by baris_a

  Hi guys, I am helping my nephew for his C lab homework, it is a string manipulation assignment and applying Wang's algorithm. Here is the BNF representation for the input. <sequent> ::= <lhs> # <rhs> <lhs> ::= <formulalist>| e <rhs> ::= <formulalist>| e <formulalist> ::= <formula>|<formula> , <formulalist> <formula> ::= <letter>| - <formula>| (<formula><in?xop><formula>) <in?xop> ::= & | | | > <letter> ::= A | B | ... | Z What is the best practice to handle and parse this kind of input in C? How can I parse this structure without using struct? Thanks in advance.

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• How do I return an array from a method?

  - by dwwilson66

  I'm trying to create a deck of cards for my homework. Code is posted below. I need to create four sets of cards (the four suits) and am create a multidimensional array. When I print the results instead of trying to pass the array, I can see that the data in the array is as expected. However, when I try to pass the array card, I get an error cannot find symbol. I've got this modeled after texbook and Java tutorial examples, and I need some help figuring out what I'm missing. I've over-documented to give an idea of how I'm thinking this SHOULD work...please let me know where I've gone horribly wrong in my understanding. import java.util.*; import java.lang.*; // public class CardGame { public static int[][] main(String[] args) { int[][] startDeck = deckOfCards(); /* cast new deck as int[][], calling method deckOfCards System.out.println(" /// from array: " + Arrays.deepToString(startDeck)); } public static int[][] deckOfCards() /* method to return a multi-dimensional array */ { int rank; int suit; for(rank=1;rank<14;rank++) /* cards 1 - 13 .... */ { for(suit=1;suit<5;suit++) /* suits 1 - 4 .... */ { int[][] card = new int[][] /* define a new card... */ { {rank,suit} /* with rank/suit from for... loops */ }; System.out.println(" /// from array: " + Arrays.deepToString(card)); } } return card; /* Error: cannot find symbol } }

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• Determining polygon intersection and containment

  - by Victor Liu

  I have a set of simple (no holes, no self-intersections) polygons, and I need to check that they don't intersect each other (one can be entirely contained in another; that is okay). I can check this by simply checking the per-vertex inside-ness of one polygon versus other polygons. I also need to determine the containment tree, which is the set of relationships that say which polygon contains any given polygon. Since no polygon can intersect any other, then any contained polygon has a unique container; the "next-bigger" one. In other words, if A contains B contains C, then A is the parent of B, and B is the parent of C, and we don't consider A the parent of C. The question: How do I efficiently determine the containment relationships and check the non-intersection criterion? I ask this as one question because maybe a combined algorithm is more efficient than solving each problem separately. The algorithm should take as input a list of polygons, given by a list of their vertices. It should produce a boolean B indicating if none of the polygons intersect any other polygon, and also if B = true, a list of pairs (P, C) where polygon P is the parent of child C. This is not homework. This is for a hobby project I am working on.

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• Python optimization problem?

  - by user342079

  Alright, i had this homework recently (don't worry, i've already done it, but in c++) but I got curious how i could do it in python. The problem is about 2 light sources that emit light. I won't get into details tho. Here's the code (that I've managed to optimize a bit in the latter part): import math, array import numpy as np from PIL import Image size = (800,800) width, height = size s1x = width * 1./8 s1y = height * 1./8 s2x = width * 7./8 s2y = height * 7./8 r,g,b = (255,255,255) arr = np.zeros((width,height,3)) hy = math.hypot print 'computing distances (%s by %s)'%size, for i in xrange(width): if i%(width/10)==0: print i, if i%20==0: print '.', for j in xrange(height): d1 = hy(i-s1x,j-s1y) d2 = hy(i-s2x,j-s2y) arr[i][j] = abs(d1-d2) print '' arr2 = np.zeros((width,height,3),dtype="uint8") for ld in [200,116,100,84,68,52,36,20,8,4,2]: print 'now computing image for ld = '+str(ld) arr2 *= 0 arr2 += abs(arr%ld-ld/2)*(r,g,b)/(ld/2) print 'saving image...' ar2img = Image.fromarray(arr2) ar2img.save('ld'+str(ld).rjust(4,'0')+'.png') print 'saved as ld'+str(ld).rjust(4,'0')+'.png' I have managed to optimize most of it, but there's still a huge performance gap in the part with the 2 for-s, and I can't seem to think of a way to bypass that using common array operations... I'm open to suggestions :D

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• C Programing - Return libcurl http response to string to the calling function

  - by empty set

  I have a homework and i need somehow to compare two http responses. I am writing it on C (dumb decision) and i use libcurl to make things easier. I am calling the function that uses libcurl to http request and response from another function and i want to return the http response to it. Anyway, the code below doesn't work, any ideas? #include <stdio.h> #include <curl/curl.h> #include <string.h> size_t write_data(void *ptr, size_t size, size_t nmemb, void *stream) { size_t written; written = fwrite(ptr, size, nmemb, stream); return written; } char *handle_url(void) { CURL *curl; char *fp; CURLcode res; char *url = "http://www.yahoo.com"; curl = curl_easy_init(); if (curl) { curl_easy_setopt(curl, CURLOPT_URL, url); curl_easy_setopt(curl, CURLOPT_WRITEFUNCTION, write_data); curl_easy_setopt(curl, CURLOPT_WRITEDATA, fp); res = curl_easy_perform(curl); if(res != CURLE_OK) fprintf(stderr, "curl_easy_perform() failed: %s\n", curl_easy_strerror(res)); curl_easy_cleanup(curl); //printf("\n%s", fp); } return fp; } This solution C libcurl get output into a string works, but not in my case because i want to return this string to the calling function.

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• python gui generate math equation

  - by Nero Dietrich

  I have a homework question for one specific item with python GUIs. My goal is to create a GUI that asks a random mathematical equation and if the equation is evaluated correctly, then I will receive a message stating that it is correct. My main problem is finding out where to place my statements so that they show up in the labels; I have 1 textbox which generates the random equation, the next textbox is blank for me to enter the solution, and then an "Enter" button at the end to evaluate my solution. It looks like this: [randomly generated equation][Empty space to enter solution] [ENTER] I've managed to get the layout and the evaluate parameters, but I don't know where to go from here. This is my code so far: class Equation(Frame): def __init__(self,parent=None): Frame.__init__(self, parent) self.pack() Equation.make_widgets(self) Equation.new_problem(self) def make_widgets(self): Label(self).grid(row=0, column=1) ent = Entry(self) ent.grid(row=0, column=1) Label(self).grid(row=0, column=2) ent = Entry(self) ent.grid(row=0, column=2) Button(self, text='Enter', command=self.evaluate).grid(row=0, column=3) def new_problem(self): pass def evaluate(self): result = eval(self.get()) self.delete(0, END) self.insert(END, result) print('Correct')

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• Code Golf: Find the possible ways on a numpad

  - by ikar

  I was bored today at school and so I tried to amuse myself using my calculator and a "game" I've invented which isn't really a game but keeps the boringness away. Also some time has passed since the last real code-golf here, so I decided to create this one. Imagine a simplified numpad like you know it from your phone (I'll leave the 0 out for this code-golf as it kinda destroys all the fun) 1 2 3 4 5 6 7 8 9 Now the rules of the game were always: At the end every digit must have been visited exactly once You can start at any digit you want You can always move one digit up, down, left or right. You can't move diagonally! There a quite a lot of possible ways (or not; I haven't found out yet), here some trivial examples: > > v v < < > > | The output of the golf-program should look something like the above, I'll try to explain: Symbols: Go right < Go left ^ Go up v Go down | End of the way Example solutions: (Program output can either be the numbers pressed in the right order from beginning point to end, or an (ASCII) picture like above) 147852369 569874123 523698741 So if we speak out the example above it would be: Start at 1, move right to 2, move right to 3, go down to 6, go left to 5, go left to 4, go down to 7, go right to 8 then go right to 9 and we are finished! Now there are many different ways possible: You could as well start at 5 and go around it in a circle. So the task would be: Write a program that can compute (using brute-force or whatever) the possible solutions for the numpad problem described above. (Friendly rethorical question with smiley removed because it made some people think that this is homework)

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• No idea how to solve SICP exercise 1.11

  - by Javier Badia

  This is not homework. Exercise 1.11: A function f is defined by the rule that f(n) = n if n<3 and f(n) = f(n - 1) + 2f(n - 2) + 3f(n - 3) if n 3. Write a procedure that computes f by means of a recursive process. Write a procedure that computes f by means of an iterative process. Implementing it recursively is simple enough. But I couldn't figure out how to do it iteratively. I tried comparing with the Fibonacci example given, but I didn't know how to use it as an analogy. So I gave up (shame on me) and Googled for an explanation, and I found this: (define (f n) (if (< n 3) n (f-iter 2 1 0 n))) (define (f-iter a b c count) (if (< count 3) a (f-iter (+ a (* 2 b) (* 3 c)) a b (- count 1)))) After reading it, I understand the code and how it works. But what I don't understand is the process needed to get from the recursive defintion of the function to this. I don't get how the code formed in someone's head. Could you explain the thought process needed to arrive at the solution?

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• Creating a Ruby method that pads an Array

  - by CJ Johnson

  I'm working on creating a method that pads an array, and accepts 1. a desired value and 2. an optional string/integer value. Desired_size reflects the desired number of elements in the array. If a string/integer is passed in as the second value, this value is used to pad the array with extra elements. I understand there is a 'fill' method that can shortcut this - but that would be cheating for the homework I'm doing. The issue: no matter what I do, only the original array is returned. I started here: class Array def pad(desired_size, value = nil) desired_size >= self.length ? return self : (desired_size - self.length).times.do { |x| self << value } end end test_array = [1, 2, 3] test_array.pad(5) From what I researched the issue seemed to be around trying to alter self's array, so I learned about .inject and gave that a whirl: class Array def pad(desired_size, value = nil) if desired_size >= self.length return self else (desired_size - self.length).times.inject { |array, x| array << value } return array end end end test_array = [1, 2, 3] test_array.pad(5) The interwebs tell me the problem might be with any reference to self so I wiped that out altogether: class Array def pad(desired_size, value = nil) array = [] self.each { |x| array << x } if desired_size >= array.length return array else (desired_size - array.length).times.inject { |array, x| array << value } return array end end end test_array = [1, 2, 3] test_array.pad(5) I'm very new to classes and still trying to learn about them. Maybe I'm not even testing them the right way with my test_array? Otherwise, I think the issue is I get the method to recognize the desired_size value that's being passed in. I don't know where to go next. Any advice would be appreciated. Thanks in advance for your time.

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• Regular expression, excluding .. in suffix of email addy

  - by user1754700

  This is homework, I've been working on it for a while, I've done lots of reading and feel I have gotten pretty familiar with regex for a beginner. I am trying to find a regular expression for validating/invalidating a list of emails. There are two addresses which are giving me problems, I can't get them both to validate the correct way at the same time. I've gone through a dozen different expressions that work for all the other emails on the list but I can't get those two at the same time. First, the addresses. [email protected] - invalid [email protected] - valid The part of my expression which validates the suffix I originally started with @.+\\.[[a-z]0-9]+ And had a second pattern for checking some more invalid addresses and checked the email against both patterns, one checked for validity the other invalidity but my professor said he wanted it all in on expression. @[[\\w]+\\.[\\w]+]+ or @[\\w]+\\.[\\w]+ I've tried it written many, many different ways but I'm pretty sure I was just using different syntax to express these two expressions. I know what I want it to do, I want it to match a character class of "character+"."character+"+ The plus sign being at least one. It works for the invalid class when I only allow the character class to repeat one time(and obviously the ip doesn't get matched), but when I allow the character class to repeat itself it matches the second period even thought it isn't preceded by a character. I don't understand why.

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• [OT a bit] Flex+JEE what is it good for?

  - by Zenzen

  Ok so sorry for being, I guess, a bit off topic but still I think this is the best place to ask. My new semester just started (don't worry I won't ask you to do my homework) and this time we have a rather cool subject about www programming in general where we have to do a web service, web abb - whatever as long as it's "web". Here's the problem though, my team and I want to do it with Flex and JEE but we don't have much experience about what are they actually used for. I mean we know you can do virtually anything with it, but we don't really want to lose time on doing something useless. My first idea was to do a "brainstorming" 3D room/service - a place where people could log in have a video conference, a whiteboard, a place to upload pictures everyone could see, some toolbars for google, youtube etc. plus some other features which would make real-time brainstorming easy when you can't get everyone in one place. But is Flex+JEE really suitable? I mean I'm 99% sure it's doable but is it really worth doing it in Flex+JEE or was the whole purpose of JEE completely different? @EDIT: well this was only one of our ideas obviously. I do know the basics of JSP, Servlets, JPA etc. of course but yeah the main goal of this project is to get some actual experience. The problem is we don't really know is it worth doing something like let's say a social network (something like extended facebook) for gamers (doesn't really matter if it already exists) in JEE or would it only look ridiculous (because PHP or whatever would be a far better choice)? Bottom line is that we are wondering are only large scale applications (for banks etc.) written in JEE or is it good for anything (even the smaller projects)?

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• Socket isn't listed by netstat unless using certain ports

  - by illuzive

  I'm a computer science student with a few years of programming experience. Yesterday, while working on a project (Mac OS X, BSD sockets) at school, I encountered a strange problem. I was adding several modules to a very basic "server" (mostly a bunch of functions to set up and manage an UDP socket on a certain port). While doing this, I started the server from time to time in order to see that everything worked like it should. I've been using port 32000 during the development of the server. When I start the server and run netstat, the socket is listed as expected. > netstat -p UDP | grep 32000 udp46 0 0 *.32000 *.* However, when I run the server on other ports (random (10000 - 50000)), it's not listed by netstat. My thought was that I had somehow hard coded the port somewhere in the code, but that's not the case. The thing is - I can connect to the socket on any of the tested ports, and it reads data sent to it without any problem at all. It just doesn't get listed by netstat. What I wonder, is if anyone of you have any idea of why this happens? Note: Although this is a project at school, it's not homework. This is just something I want to understand for my own benefit.

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• BASH: How to count all the human readable files?

  - by user1687406

  I'm taking an intro course to UNIX and have a homework question that follows: How many files in the previous question are text files? A text file is any file containing human-readable content. (TRICK QUESTION. Run the file command on a file to see whether the file is a text file or a binary data file! If you simply count the number of files with the ".txt" extension you will get no points for this question.) The previous question simply asked how many regular files there were, which was easy to figure out by doing find . -type f | wc -l I'm just having trouble determining what "human readable content" is, since I'm assuming it means anything besides binary/assembly, but I thought that's what -type f displays. Maybe that's what the professor meant by saying "trick question"? This question has a follow up later that also asks "What text files contain the string "csc" in any mix of upper and lower case?". Obviously "text" is referring to more than just .txt files, but I need to figure out the first question to determine this!

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• Getting the avg of the top 10 students from each school

  - by dave

  Hi all -- We have a school district with 38 elementary schools. The kids took a test. The averages for the schools are widely dispersed, but I want to compare the averages of JUST THE TOP 10 students from each school. Requirement: use temporary tables only. I have done this in a very work-intensive, error-prone sort of way as follows. (sch_code = e.g., 9043; -- schabbrev = e.g., "Carter"; -- totpct_stu = e.g., 61.3) DROP TEMPORARY TABLE IF EXISTS avg_top10 ; CREATE TEMPORARY TABLE avg_top10 ( sch_code VARCHAR(4), schabbrev VARCHAR(75), totpct_stu DECIMAL(5,1) ); INSERT INTO avg_top10 SELECT sch_code , schabbrev , totpct_stu FROM test_table WHERE sch_code IN ('5489') ORDER BY totpct_stu DESC LIMIT 10; -- I do that last query for EVERY school, so the total -- length of the code is well in excess of 300 lines. -- Then, finally... SELECT schabbrev, ROUND( AVG( totpct_stu ), 1 ) AS top10 FROM avg_top10 GROUP BY schabbrev ORDER BY top10 ; -- OUTPUT: ----------------------------------- schabbrev avg_top10 ---------- --------- Goulding 75.4 Garth 77.7 Sperhead 81.4 Oak_P 83.7 Spring 84.9 -- etc... Question: So this works, but isn't there a lot better way to do it? Thanks! PS -- Looks like homework, but this is, well...real.

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• MySQL " identify storage engine statement"

  - by sammysmall

  This IS NOT a Homework question! While building my current student database project I realized that I may want to identify comprehensive information about a database design in the future. More-so if I am fortunate enough to get a job in this field and were handed a database project how could I break down certain elements for identification... In all of my previous designs I have been using MySQL Community Server (GPL) 5.1.42, I thought (duh) that I was using the MyISAM based on most of my text-book instruction and MySQL 5.0 Reference Manual :: 13 Storage Engines :: 13.1 The MyISAM Storage Engine I determined that this was in fact incorrect for this version and the use of "SHOW ENGINES" at the console... No problem, figured out why they have "versions" the need to pay attention to what version is being used, and the need for a means to determine what I am about to mess up "if" I do not pay attention to detail... Q1. Specifically what statement will identify the version used by someone elses initial database creation? (since I created my own databases I know what version I used) Q2. Specifically what statement will identify the storage engine that the developer used when creating the database. (I specified a particular database in my collection then tried SHOW Engine, did not work, then tried to just get the metadata from one table in that database: mysql SELECT duck_cust, table_type, engine - FROM INFORMATION_SCHEMA.tables - WHERE table_schema = 'tp' - ORDER BY table_type ASC, table_name DESC; as this was not really what I wanted (and did not work) I am looking for some direction from the pros... Q3. (If you really have the inclination to continue helping) If I were to access a database from an earlier/later "version" are there backward/forward compatibility issues for maintaining/updating data between versions? Please and Thank you in advance for your time and efforts! sammysmall

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• java phone number validation....

  - by user69514

  Here is my problem: Create a constructor for a telephone number given a string in the form xxx-xxx-xxxx or xxx-xxxx for a local number. Throw an exception if the format is not valid. So I was thinking to validate it using a regular expression, but I don't know if I'm doing it correctly. Also what kind of exception would I have to throw? Do I need to create my own exception? public TelephoneNumber(String aString){ if(isPhoneNumberValid(aString)==true){ StringTokenizer tokens = new StringTokenizer("-"); if(tokens.countTokens()==3){ areaCode = Integer.parseInt(tokens.nextToken()); exchangeCode = Integer.parseInt(tokens.nextToken()); number = Integer.parseInt(tokens.nextToken()); } else if(tokens.countTokens()==2){ exchangeCode = Integer.parseInt(tokens.nextToken()); number = Integer.parseInt(tokens.nextToken()); } else{ //throw an excemption here } } } public static boolean isPhoneNumberValid(String phoneNumber){ boolean isValid = false; //Initialize reg ex for phone number. String expression = "(\\d{3})(\\[-])(\\d{4})$"; CharSequence inputStr = phoneNumber; Pattern pattern = Pattern.compile(expression); Matcher matcher = pattern.matcher(inputStr); if(matcher.matches()){ isValid = true; } return isValid; } Hi sorry, yes this is homework. For this assignments the only valid format are xxx-xxx-xxxx and xxx-xxxx, all other formats (xxx)xxx-xxxx or xxxxxxxxxx are invalid in this case. I would like to know if my regular expression is correct

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• Scalability 101: How can I design a scalable web application using PHP?

  - by Legend

  I am building a web-application and have a couple of quick questions. From what I learnt, one should not worry about scalability when initially building the app and should only start worrying when the traffic increases. However, this being my first web-application, I am not quite sure if I should take an approach where I design things in an ad-hoc manner and later "fix" them. I have been reading stories about how people start off with an app that gets millions of users in a week or two. Not that I will face the same situation but I can't help but wonder, how do these people do it? Currently, I bought a shared hosting account on Lunarpages and that got me started in building and testing the application. However, I am interested in learning how to build the same application in a scalable-manner using the cloud, for instance, Amazon's EC2. From my understanding, I can see a couple of components: There is a load balancer that first receives requests and then decides where to route each request This request is then handled by a server replica that then processes the request and updates (if required) the database and sends back the response to the client If a similar request comes in, then a caching mechanism like memcached kicks into picture and returns objects from the cache A blackbox that handles database replication Specifically, I am trying to do the following: Setting up a load balancer (my homework revealed that HAProxy is one such load balancer) Setting up replication so that databases can be synchronized Using memcached Configuring Apache to work with multiple web servers Partitioning application to use Amazon EC2 and Amazon S3 (my application is something that will need great deal of storage) Finally, how can I avoid burning myself when using Amazon services? Because this is just a learning phase, I can probably do with 2-3 servers with a simple load balancer and replication but until I want to avoid paying loads of money accidentally. I am able to find resources on individual topics but am unable to find something that starts off from the big picture. Can someone please help me get started?

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• algorithm to find longest non-overlapping sequences

  - by msalvadores

  I am trying to find the best way to solve the following problem. By best way I mean less complex. As an input a list of tuples (start,length) such: [(0,5),(0,1),(1,9),(5,5),(5,7),(10,1)] Each element represets a sequence by its start and length, for example (5,7) is equivalent to the sequence (5,6,7,8,9,10,11) - a list of 7 elements starting with 5. One can assume that the tuples are sorted by the start element. The output should return a non-overlapping combination of tuples that represent the longest continuos sequences(s). This means that, a solution is a subset of ranges with no overlaps and no gaps and is the longest possible - there could be more than one though. For example for the given input the solution is: [(0,5),(5,7)] equivalent to (0,1,2,3,4,5,6,7,8,9,10,11) is it backtracking the best approach to solve this problem ? I'm interested in any different approaches that people could suggest. Also if anyone knows a formal reference of this problem or another one that is similar I'd like to get references. BTW - this is not homework. Edit Just to avoid some mistakes this is another example of expected behaviour for an input like [(0,1),(1,7),(3,20),(8,5)] the right answer is [(3,20)] equivalent to (3,4,5,..,22) with length 20. Some of the answers received would give [(0,1),(1,7),(8,5)] equivalent to (0,1,2,...,11,12) as right answer. But this last answer is not correct because is shorter than [(3,20)].

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• C++, generic programming and virtual functions. How do I get what I want?

  - by carleeto

  This is what I would like to do using templates: struct op1 { virtual void Method1() = 0; } ... struct opN { virtual void MethodN() = 0; } struct test : op1, op2, op3, op4 { virtual void Method1(){/*do work1*/}; virtual void Method2(){/*do work2*/}; virtual void Method3(){/*do work3*/}; virtual void Method4(){/*do work4*/}; } I would like to have a class that simply derives from a template class that provides these method declarations while at the same time making them virtual. This is what I've managed to come up with: #include <iostream> template< size_t N > struct ops : ops< N - 1 > { protected: virtual void DoStuff(){ std::cout<<N<<std::endl; }; public: template< size_t i > void Method() { if( i < N ) ops<i>::DoStuff(); } //leaving out compile time asserts for brevity } struct test : ops<6> { }; int main( int argc, char ** argv ) { test obj; obj.Method<3>(); //prints 3 return 0; } However, as you've probably guessed, I am unable to override any of the 6 methods I have inherited. I'm obviously missing something here. What is my error? No, this isn't homework. This is curiosity.

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• Copy a LinkedList that has a Random Pointer in it

  - by Bragaadeesh

  Hi, First of all this is not a homework, this is an interview question that I got from a company I attended today. You have a singly linked list with the Node structure as the following class Node{ int data; Node next; Node random; } You have a typical singly linked list of length n. The random pointer in each node in the linkedlist randomly points to some Node within the linked list. The Question is to create a copy of the linked list efficiently into a different LinkedList. I said that I will first calculate the Random pointer's position in the linked list and store it in an array. Then create a new linked list normally. Then iterate through the linked list by setting the random pointer where they belong by reading the values stored from the array. I know its a very brute force technique and the interviewer asked me to come up with a better solution but I couldnt. Please can someone answer this? I can explain if the question is not clear.

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• Including Data From DropDownList Into Gridview

  - by Mike Keller

  I feel a little embarassed posting two questions relating to the same problem, but the first one ended up answering a question that I believe is unrelated to the solution so I'm leaving it up and outlining what I'm trying to accomplish with the hopes that someone can help out a .Net noob. What I need to be able to do is create a field in my gridview that contains a link that passes two variables. One is pulled from within the gridviews datasource and the other needs to be pulled from a textbox control outside the gridview. From what I've read so far you cannot use a hyperlinkfield for this as the datanavigateurlfields cannot be set to pull from anything but the gridview's data source. What I attempted to do was create a template field where in the itemtemplate I called: <a href="example.aspx?e=<%# Eval(ExampleList.SelectedItem.Value) %>">Test</a> That comes back with an error like this: DataBinding: 'System.Data.DataRowView' does not contain a property with the value 'TestData' Any clues to make this happen would be appreciated, like I said I'm pretty new to .Net so please be gentle. I tried to do my homework before posting this.

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• Convert a binary tree to linked list, breadth first, constant storage/destructive

  - by Merlyn Morgan-Graham

  This is not homework, and I don't need to answer it, but now I have become obsessed :) The problem is: Design an algorithm to destructively flatten a binary tree to a linked list, breadth-first. Okay, easy enough. Just build a queue, and do what you have to. That was the warm-up. Now, implement it with constant storage (recursion, if you can figure out an answer using it, is logarithmic storage, not constant). I found a solution to this problem on the Internet about a year back, but now I've forgotten it, and I want to know :) The trick, as far as I remember, involved using the tree to implement the queue, taking advantage of the destructive nature of the algorithm. When you are linking the list, you are also pushing an item into the queue. Each time I try to solve this, I lose nodes (such as each time I link the next node/add to the queue), I require extra storage, or I can't figure out the convoluted method I need to get back to a node that has the pointer I need. Even the link to that original article/post would be useful to me :) Google is giving me no joy. Edit: Jérémie pointed out that there is a fairly simple (and well known answer) if you have a parent pointer. While I now think he is correct about the original solution containing a parent pointer, I really wanted to solve the problem without it :) The refined requirements use this definition for the node: struct tree_node { int value; tree_node* left; tree_node* right; };

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