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• Learning Algorithms and Data Structures Fundamentals

  - by valya

  Can you recommend me a book or (better!) a site with many hard problems and exercises about data structures? I'm already answering project Euler questions, but these questions are about interesting, but uncommon algorithms. I hardly used even a simple tree. Maybe there is a site with exercises like: hey, you need to calculate this: ... . Do it using a tree. Now do it using a zipper. Upload your C (Haskell, Lisp, even Pascal or Fortress go) solution. Oh, your solution is so slow! Self-education is very hard then you trying to learn very common, fundamental things. How can I help myself with them without attending to courses or whatever?

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• Converting a jQuery plugin to work on all objects, not just the DOM

  - by Jon Winstanley

  I am using the jQuery physics plugin for a pet project I am working on. The plugin enables the moving of DOM objects in realistic ways using velocity, gravity, wind etc. However I want to use the plugin to calculate where objects are to be placed inside a canvas element, not DOM object. How do I change the plugin script to work for ANY object with 'top' and 'left' properties rather than only working with DOM objects found with a jQuery selector? Currently the script functions look like this: jQuery.fn.funname = function() { return this; };

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• changing output in objective-c app

  - by Zack

  // // RC4.m // Play5 // // Created by svp on 24.05.10. // Copyright 2010 __MyCompanyName__. All rights reserved. // #import "RC4.h" @implementation RC4 @synthesize txtLyrics; @synthesize sbox; @synthesize mykey; - (IBAction) clicked: (id) sender { NSData *asciidata1 = [@"4875" dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES]; NSString *asciistr1 = [[NSString alloc] initWithData:asciidata1 encoding:NSASCIIStringEncoding]; //[txtLyrics setText:@"go"]; NSData *asciidata = [@"sdf883jsdf22" dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES]; NSString *asciistr = [[NSString alloc] initWithData:asciidata encoding:NSASCIIStringEncoding]; //RC4 * x = [RC4 alloc]; [txtLyrics setText:[self decrypt:asciistr1 andKey:asciistr]]; } - (NSMutableArray*) hexToChars: (NSString*) hex { NSMutableArray * arr = [[NSMutableArray alloc] init]; NSRange range; range.length = 2; for (int i = 0; i < [hex length]; i = i + 2) { range.location = 0; NSString * str = [[hex substringWithRange:range] uppercaseString]; unsigned int value; [[NSScanner scannerWithString:str] scanHexInt:&value]; [arr addObject:[[NSNumber alloc] initWithInt:(int)value]]; } return arr; } - (NSString*) charsToStr: (NSMutableArray*) chars { NSString * str = @""; for (int i = 0; i < [chars count]; i++) { str = [NSString stringWithFormat:@"%@%@",[NSString stringWithFormat:@"%c", [chars objectAtIndex:i]],str]; } return str; } //perfect except memory leaks - (NSMutableArray*) strToChars: (NSString*) str { NSData *asciidata = [str dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES]; NSString *asciistr = [[NSString alloc] initWithData:asciidata encoding:NSASCIIStringEncoding]; NSMutableArray * arr = [[NSMutableArray alloc] init]; for (int i = 0; i < [str length]; i++) { [arr addObject:[[NSNumber alloc] initWithInt:(int)[asciistr characterAtIndex:i]]]; } return arr; } - (void) initialize: (NSMutableArray*) pwd { sbox = [[NSMutableArray alloc] init]; mykey = [[NSMutableArray alloc] init]; int a = 0; int b; int c = [pwd count]; int d = 0; while (d < 256) { [mykey addObject:[pwd objectAtIndex:(d % c)]]; [sbox addObject:[[NSNumber alloc] initWithInt:d]]; d++; } d = 0; while (d < 256) { a = (a + [[sbox objectAtIndex:d] intValue] + [[mykey objectAtIndex:d] intValue]) % 256; b = [[sbox objectAtIndex:d] intValue]; [sbox replaceObjectAtIndex:d withObject:[sbox objectAtIndex:a]]; [sbox replaceObjectAtIndex:a withObject:[[NSNumber alloc] initWithInt:b]]; d++; } } - (NSMutableArray*) calculate: (NSMutableArray*) plaintxt andPsw: (NSMutableArray*) psw { [self initialize:psw]; int a = 0; int b = 0; NSMutableArray * c = [[NSMutableArray alloc] init]; int d; int e; int f; int g = 0; while (g < [plaintxt count]) { a = (a + 1) % 256; b = (b + [[sbox objectAtIndex:a] intValue]) % 256; e = [[sbox objectAtIndex:a] intValue]; [sbox replaceObjectAtIndex:a withObject:[sbox objectAtIndex:b]]; [sbox replaceObjectAtIndex:b withObject:[[NSNumber alloc] initWithInt:e]]; int h = ([[sbox objectAtIndex:a]intValue] + [[sbox objectAtIndex:b]intValue]) % 256; d = [[sbox objectAtIndex:h] intValue]; f = [[plaintxt objectAtIndex:g] intValue] ^ d; [c addObject:[[NSNumber alloc] initWithInt:f]]; g++; } return c; } - (NSString*) decrypt: (NSString*) src andKey: (NSString*) key { NSMutableArray * plaintxt = [self hexToChars:src]; NSMutableArray * psw = [self strToChars:key]; NSMutableArray * chars = [self calculate:plaintxt andPsw:psw]; NSData *asciidata = [[self charsToStr:chars] dataUsingEncoding:NSASCIIStringEncoding allowLossyConversion:YES]; NSString *asciistr = [[NSString alloc] initWithData:asciidata encoding:NSUTF8StringEncoding]; return asciistr; } @end This is supposed to decrypt a hex string with an ascii string, using rc4 decryption. I'm converting my java application to objective-c. The output keeps changing, every time i run it.

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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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• Will Multi threading increase the speed of the calculation on Single Processor

  - by Harsha

  On a single processor, Will multi-threading increse the speed of the calculation. As we all know that, multi-threading is used for Increasing the User responsiveness and achieved by sepating UI thread and calculation thread. But lets talk about only console application. Will multi-threading increases the speed of the calculation. Do we get culculation result faster when we calculate through multi-threading. what about on multi cores, will multi threading increse the speed or not. Please help me. If you have any material to learn more about threading. please post. Thanks in advance, Harsha

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• How to send reminder emails based on users input time and day (based on their time zone)

  - by evgelen

  I need to send emails based on users input time and day (based on their time zone)? Kind of a reminder. For Example: User input 2:00pm Eastern Time on my server I have different time zone, how to calculate the time and send the email at users time-zone. Its a web application. What is the best way to accomplish it using asp.net c#? If somebody already done it in the past I will be glad to take a look at source code. Thank you for useful suggestions.

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• Randomized experiments in R

  - by gd047

  Here is a simple randomized experiment. In the following code I calculate the p-value under the null hypothesis that two different fertilizers applied to tomato plants have no effect in plants yields. The first random sample (x) comes from plants where a standard fertilizer has been used, while an "improved" one has been used in the plants where the second sample (y) comes from. x <- c(11.4,25.3,29.9,16.5,21.1) y <- c(23.7,26.6,28.5,14.2,17.9,24.3) total <- c(x,y) first <- combn(total,length(x)) second <- apply(first,2,function(x) total[!total %in% x]) dif.treat <- apply(second,2,mean) - apply(first,2,mean) # the first element of dif.treat is the one that I'm interested in (p.value <- length(dif.treat[dif.treat >= dif.treat[1]]) / length(dif.treat)) Do you know of any R function that performs tests like this one?

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• Implement the Combine function using templates

  - by gkid123

  any idea on how to do it for template? thanks Implement the Combine function using templates. The Combine fn applies a function of two arguments cumulatively to the items of an STL container, from begin() to end(), so as to reduce the sequence to a single value. For example, Combine(<list containing 6,3,1,9,7>, std::plus<int>()) should calculate ((((6+3)+1)+9)+7). class NotEnoughElements {}; template <typename Container, typename Function> typename Container::value_type Combine(const Container& c, Function fn) throw (NotEnoughElements) { your code goes here }

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• Wunderground and UTC Offset

  - by Brandon

  I am consuming the international weather forecasts via Wunderground's XML API: http://wiki.wunderground.com/index.php/API_-_XML Looking at an output for Kabul, Afghanistan for instance: http://api.wunderground.com/auto/wui/geo/ForecastXML/index.xml?query=OAKB I notice that there is no UTC offset. The closest that I can see is this: <tz_short>AFT</tz_short> Which identifies the current TimeZone is AFT. The problem I see is that there is no universally accepted time zone abbreviations, so I cannot take these abbreviations and look up and offset from C#'s TimeZoneInfo objects. Is there a listing of Wunderground's Time Zones abbreviations/names/offsets so I can map their Time Zones to the TimeZoneInfo objects, or is there a better way to get this information? I will need to use the TimeZoneInfo so I can calculate daylight savings time for different locations internationally.

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• Division to the nearest 1 decimal place without floating point math?

  - by John Sheares

  I am having some speed issues with my C# program and identified that this percentage calculation is causing a slow down. The calculation is simply n/d * 100. Both the numerator and denominator can be any integer number. The numerator can never be greater than the denominator and is never negative. Therefore, the result is always from 0-100. Right now, this is done by simply using floating point math and is somewhat slow, since it's being calculated tens of millions of times. I really don't need anything more accurate than to the nearest 0.1 percent. And, I just use this calculated value to see if it's bigger than a fixed constant value. I am thinking that everything should be kept as an integer, so the range with 0.1 accuracy would be 0-1000. Is there some way to calculate this percentage without floating point math?

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• extracting a quadrilateral image to a rectangle

  - by Will

  In the image below, the sign on the side of the van is not face-on to the camera. I want to calculate, as best I can with the pixels I have, what it'd look like face on. I imagine that this is some kind of loop through the x and y axis doing a Bresenham's line on both dimensions at once with some kind of mixing when pixels in the source image overlap - some sub-pixel mixing of some sort? What approaches are there, and how do you mix the pixels? Is there a standard approach for this?

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• recursive program

  - by wilson88

  I am trying to make a recursive program that calculates interest per year.It prompts the user for the startup amount (1000), the interest rate (10%)and number of years(1).(in brackets are samples) Manually I realised that the interest comes from the formula YT(1 + R)----- interest for the first year which is 1100. 2nd year YT(1 + R/2 + R2/2) //R squared 2nd year YT(1 + R/3 + R2/3 + 3R3/) // R cubed How do I write a recursive program that will calculate the interest? Below is the function which I tried double calculateInterest(double startUp, double rate, double duration) { double cpdInterest = (duration*startUp)*(1 + rate); if (duration == 0) { return cpdInterest; } else if (duration < 0) { cout << "Please enter a valid year"; } else { calculateInterest(cpdInterest,rate,duration); } return cpdInterest; }

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• How to visually represent file size

  - by Keith Williams

  This will be a bit subjective, I'm afraid, but I'd value the advice of the Collective. Our web application lists documents that users can download; standard file navigator stuff: Type Name Created Size ----------------------------------- PDF Doc 1 01/04/2010 15 KB PDF Doc 2 01/04/2010 15 MB Currently we list the file size as text, but I'd like to improve this by having some way of showing visually whether the file is tiny, normal or huge. The reason for this is so that users can scan the list quickly and spot files that are likely to take a long time downloading. My options currently are: Bigger font sizes for bigger files (drawback: the layout can become untidy) Icons (like a wi-fi signal strength indicator; drawback: harder to scan) Keep all sizes in KB so the number of zeroes indicates size (drawback: users have to calculate the "friendly" size in their heads) I know this is quite a minor thing, but I'd appreciate anyone's thoughts on the matter!

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• Including tax in total sale price.

  - by Frank Computer

  INFORMIX-SQL 7.3 Perform Screen: Suppose I have a customer who wants to pay a $100 (7% tax included), what logic can I use so that when the cashier clerk enters $100 in the tax included sale amount, it will calculate the sale price and tax so that it adds up to $100. I have the folllowing 3 field tags in my perform screen: sprice = transaction.sale_price; stax = transaction.sale_tax; stotal = transaction.sale_total; after editadd of transaction.sale_price ? ? ?

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• MySQL indexes: how do they work?

  - by bob-the-destroyer

  I'm a complete newbie with MySQL indexes. I have several MyISAM tables on MySQL 5.0x having utf8 charsets and collations with 100k+ records each. The primary keys are generally integer. Many columns on each table may have duplicate values. I need to quickly count, sum, average, or otherwise perform custom calculations on any number of fields in each table or joined on any number of others. I found this page giving an overview of MySQL index usage: http://dev.mysql.com/doc/refman/5.0/en/mysql-indexes.html, but I'm still not sure I'm using indexes right. Just when I think I've made the perfect index out of a collection of fields I want to calculate against, I get the "index must be under 1000 bytes" error. Can anyone explain how to most efficiently create and use indexes to speed up queries? Caveat: upgrading Mysql is not possible in this case. Using Navicat Light for db administration, but this app isn't required.

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• charts, forms and credit card payment in drupal

  - by mingos

  Hey. I've got this client who's a dietician and wants a site with some functionality I'm not sure how to implement: custom forms that calculate some stuff (like ideal body weight, based on a bazillion factors), the user is supposed to be able to pay for the consultation with a credit card - which lets him access more consultation forms, bi-weekly results from how a user's diet is going (weight reduction and so on) should be displayed using a series of charts, preferably in the user's account page. I use Drupal exclusively, so the question is whether such functionality can be implemented using existing modules? Which modules would you recommend? Can this be achieved without writing custom modules (I've never written a Drupal module)? Thanks in advance for your suggestions.

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• Nesting maximum amount of shapes on a surface

  - by Fuu

  In industry, there is often a problem where you need to calculate the most efficient use of material, be it fabric, wood, metal etc. So the starting point is X amount of shapes of given dimensions, made out of polygons and/or curved lines, and target is another polygon of given dimensions. I assume many of the current CAM suites implement this, but having no experience using them or of their internals, what kind of computational algorithm is used to find the most efficient use of space? Can someone point me to a book or other reference that discusses this topic?

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• Excel 2003 - ADDRESS() function issues

  - by hairdresser-101

  I finally thought I had found a way to acutally use excel productively but the code that I followed does not appear to work. I'm thinking that the code is very limited and can't do what I want but I thought I'd ask to confirm - maybe it is my function that is the problem. I want to calculate the sum of a row of values for the previous month based on how many days we are into this month (i.e. It is the 20th of April so I want to sum the first 20 days of March to compare against.) =SUM(G4:ADDRESS(ROW(),7+$BR$3,4)) I basically want to SUM(G4:AA4) and have used the address function to return the cell reference AA4 by taking G4 and adding 20 to the column count. ADDRESS(ROW(),7+$BR$3,4) This successfully returns AA7 as expected HOWEVER, when I try to use the returning value in the SUM() function it throws an error... Am I not able to use this reference in my calculation?

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• translating ROI code in c#

  - by sayyad

  Hi, I am trying to translate this code in c# using emgucv. I have some questions.Could yome body help me line by line. cvSetImageROI(img1, cvRect(10, 15, 150, 250)); I have four points (PoinstF). Should I calculate rectangle or there is some way with four points. CvInvoke.cvSetImageROI(img1, ------------(how can I declare cvReCt(10, 15, 150, 250)); //c# IplImage *img2 = cvCreateImage(cvGetSize(img1), img1-depth, img1-nChannels); //c# Image img2; // i supose i needn't to allocate memory.//c# cvCopy(img1, img2, NULL); CvInvoke.cvCopy(img1, img2, IntPtr.Zero);//c# cvResetImageROI(img1); shoul i ResetImageROI.//c# thanx and best regards,

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• Recursive function causing a stack overflow

  - by dbyrne

  I am trying to write a simple sieve function to calculate prime numbers in clojure. I've seen this question about writing an efficient sieve function, but I am not to that point yet. Right now I am just trying to write a very simple (and slow) sieve. Here is what I have come up with: (defn sieve [potentials primes] (if-let [p (first potentials)] (recur (filter #(not= (mod % p) 0) potentials) (conj primes p)) primes)) For small ranges it works fine, but causes a stack overflow for large ranges: user=> (sieve (range 2 30) []) [2 3 5 7 11 13 17 19 23 29] user=> (sieve (range 2 15000) []) java.lang.StackOverflowError (NO_SOURCE_FILE:0) I thought that by using recur this would be a non-stack-consuming looping construct? What am I missing?

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• calculating a gps coordinate given a point, bearing and distance

  - by user530509

  Hello, I have a problem which draws my back in some project for some time now. Im basically looking to trap a polygon using x,y points drawn by some script ive written. lat1,lon1 are the center gps cords of the polygon and im looking for its surrounding polygon. here is a part of my code in python: def getcords(lat1,lon1,dr,bearing): lat2=asin(sin(lat1)*cos(dr)+cos(lat1)*sin(dr)*cos(bearing)) lon2=lon1+atan2(sin(bearing)*sin(dr)*cos(lat1),cos(dr)-sin(lat1)*sin(lat2)) return [lat2,lon2] my input goes like this: lat1,lon1 - are given in decimal degrees. -dr is the angular computed by dividing the distance in miles by the earth's -raiuds(=3958.82) -bearing between 0-360 degrees. however for the input getcorsds1(42.189275,-76.85823,0.5/3958.82,30) i get [-1.3485899508698462, -76.8576637627568], however [42.2516666666667,-76.8097222222222] is the right answer. as for the angular distance i calculate it simply by dividing the distance in miles by the earth's raiuds(=3958.82). anybody?

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• HTML 5 Canvas - Get pixel data for a path

  - by Mikey S.

  I wonder if is there any way I can get pixel data for the currently drawn path in the canvas tag. I can calculate the pixel data on my own when drawing simple shapes like square or a line, but things get messy with more complicated shapes like ellipse or even a simple circle. The reason i'm asking this is because I'm working on a web application which involves sending canvas pixels data to the server when I add a path to the canvas. The server needs to keep it's own copy of the entire canvas, and I really don't want to send the ENTIRE canvas image every single change, but only the delta for efficiency reasons... Thanks.

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• Compiler error when casting to function pointer

  - by detly

  I'm writing a bootloader for the PIC32MX, using HiTech's PICC32 compiler (similar to C90). At some point I need to jump to the real main routine, so somewhere in the bootloader I have void (*user_main) (void); user_main = (void (*) (void)) 0x9D003000; user_main(); (Note that in the actual code, the function signature is typedef'd and the address is a macro.) I would rather calculate that (virtual) address from the physical address, and have something like: void (*user_main) (void); user_main = (void (*) (void)) (0x1D003000 | 0x80000000); user_main(); ...but when I try that I get a compiler error: Error #474: ; 0: no psect specified for function variable/argument allocation Have I tripped over some vagarity of C syntax here? This error doesn't reference any particular line, but if I comment out the user_main() call, it goes away. (This might be the compiler removing a redundant code branch, but the HiTech PICC32 isn't particularly smart in Lite mode, so maybe not.)

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• Calculating the pixel size of a string with Python

  - by Aristide

  I have a Python script which needs to calculate the exact size of arbitrary strings displayed in arbitrary fonts in order to generate simple diagrams. I can easily do it with Tkinter. The problem is the results seem to depend on the version of Python and/or the system. import Tkinter as tk import tkFont root = tk.Tk() times12 = tkFont.Font(family="times",size=12) print times12.metrics("linespace"), print times12.measure("Hello world") times24 = tkFont.Font(family="times",size=24) print times24.metrics("linespace"), print times24.measure("Hello world") Python 2.5 on Mac OS X gives the actual pixel measurements: 12 57 24 116 Python 2.6.1 on Mac OS X gives: 14 58 27 115 Python 2.6.3 on Windows XP gives: 19 71 36 154 Such a need being quite common, I suspect I did something wrong. Any idea?

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• Calculating the union of 2 longitudal intervals (that may wrap around 180 degrees)

  - by timpatt

  The story: I have a LatLongBounds class that represents an area on the surface of the earth by a latitudinal interval (bounded by north & south - not important to this question) and a longitudinal interval (bounded by east and west; both normalized to a range [-180, 180] - negative being a westerly direction). In order to be able to represent an area that straddles the 180 degree meridian the value of west may be set to be greater than east (eg. the range west = 170, east = -170 will straddle said meridian). In effect the longitudinal interval may wrap around at 180 degrees (or equivalently -180 degrees). My Question: Does anyone have any suggestions as to how I can calculate the union of two longitudinal intervals that may wrap around at 180 degrees. Thanks.

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