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• question about qsort in c++

  - by davit-datuashvili

  i have following code in c++ #include <iostream> using namespace std; void qsort5(int a[],int n){ int i; int j; if (n<=1) return; for (i=1;i<n;i++) j=0; if (a[i]<a[0]) swap(++j,i,a); swap(0,j,a); qsort5(a,j); qsort(a+j+1,n-j-1); } int main() { return 0; } void swap(int i,int j,int a[]) { int t=a[i]; a[i]=a[j]; a[j]=t; } i have problem 1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(13) : error C2780: 'void std::swap(std::basic_string<_Elem,_Traits,_Alloc> &,std::basic_string<_Elem,_Traits,_Alloc> &)' : expects 2 arguments - 3 provided 1> c:\program files\microsoft visual studio 9.0\vc\include\xstring(2203) : see declaration of 'std::swap' 1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(13) : error C2780: 'void std::swap(std::pair<_Ty1,_Ty2> &,std::pair<_Ty1,_Ty2> &)' : expects 2 arguments - 3 provided 1> c:\program files\microsoft visual studio 9.0\vc\include\utility(76) : see declaration of 'std::swap' 1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(13) : error C2780: 'void std::swap(_Ty &,_Ty &)' : expects 2 arguments - 3 provided 1> c:\program files\microsoft visual studio 9.0\vc\include\utility(16) : see declaration of 'std::swap' 1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(14) : error C2780: 'void std::swap(std::basic_string<_Elem,_Traits,_Alloc> &,std::basic_string<_Elem,_Traits,_Alloc> &)' : expects 2 arguments - 3 provided 1> c:\program files\microsoft visual studio 9.0\vc\include\xstring(2203) : see declaration of 'std::swap' 1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(14) : error C2780: 'void std::swap(std::pair<_Ty1,_Ty2> &,std::pair<_Ty1,_Ty2> &)' : expects 2 arguments - 3 provided 1> c:\program files\microsoft visual studio 9.0\vc\include\utility(76) : see declaration of 'std::swap' 1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(14) : error C2780: 'void std::swap(_Ty &,_Ty &)' : expects 2 arguments - 3 provided 1> c:\program files\microsoft visual studio 9.0\vc\include\utility(16) : see declaration of 'std::swap' 1>c:\users\dato\documents\visual studio 2008\projects\qsort5\qsort5\qsort5.cpp(16) : error C2661: 'qsort' : no overloaded function takes 2 arguments 1>Build log was saved at "file://c:\Users\dato\Documents\Visual Studio 2008\Projects\qsort5\qsort5\Debug\BuildLog.htm" please help

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• Calculating holidays

  - by Ralph Shillington

  A number of holidays move around from year to year. For example, in Canada Victoria day (aka the May two-four weekend) is the Monday before May 25th, or Thanksgiving is the 2nd Monday of October (in Canada). I've been using variations on this Linq query to get the date of a holiday for a given year: var year = 2011; var month = 10; var dow = DayOfWeek.Monday; var instance = 2; var day = (from d in Enumerable.Range(1,DateTime.DaysInMonth(year,month)) let sample = new DateTime(year,month,d) where sample.DayOfWeek == dow select sample).Skip(instance-1).Take(1); While this works, and is easy enough to understand, I can imagine there is a more elegant way of making this calculation versus this brute force approach. Of course this doesn't touch on holidays such as Easter and the many other lunar based dates.

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• What is the data structure behind google suggest?

  - by anony

  if we have some search terms with frequency, how do I suggest the top 5 frequently searched words? The data structure used must be easily updatable.(for eg: if I want to update frequency of a term or add a new term etc...)

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• Retrieving the top 100 numbers from one hundred million of numbers

  - by didxga

  One of my friend been asked with a question, Retrieving the max top 100 numbers from one hundred million of numbers, in a recent job interview. Do you have any idea to come up with an efficient way to solve it? regards!

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• Genetic programming in c++, library suggestions?

  - by shuttle87

  I'm looking to add some genetic algorithms to an Operations research project I have been involved in. Currently we have a program that aids in optimizing some scheduling and we want to add in some heuristics in the form of genetic algorithms. Are there any good libraries for generic genetic programming/algorithms in c++? Or would you recommend I just code my own? I should add that while I am not new to c++ I am fairly new to doing this sort of mathematical optimization work in c++ as the group I worked with previously had tended to use a proprietary optimization package. We have a fitness function that is fairly computationally intensive to evaluate and we have a cluster to run this on so parallelized code is highly desirable. So is c++ a good language for this? If not please recommend some other ones as I am willing to learn another language if it makes life easier. thanks!

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• Why does Java's hashCode() in String use 31 as a multiplier?

  - by jacobko

  In Java, the hash code for a String object is computed as s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1] using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. Why is 31 used as a multiplier? I understand that the multiplier should be a relatively large prime number. So why not 29, or 37, or even 97?

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• how to develop a program to minimize errors in human transcription of hand written surveys

  - by Alex. S.

  I need to develop custom software to do surveys. Questions may be of multiple choice, or free text in a very few cases. I was asked to design a subsystem to check if there is any error in the manual data entry for the multiple choices part. We're trying to speed up the user data entry process and to minimize human input differences between digital forms and the original questionnaires. The surveys are filled with handwritten marks and text by human interviewers, so it's possible to find hard to read marks, or also the user could accidentally select a different value in some question, and we would like to avoid that. The software must include some automatic control to detect possible typing differences. Each answer of the multiple choice questions has the same probability of being selected. This question has two parts: The GUI. The most simple thing I have in mind is to implement the most usable design of the questions display: use of large and readable fonts and space generously the choices. Is there something else? For faster input, I would like to use drop down lists (favoring keyboard over mouse). Given the questions are grouped in sections, I would like to show the answers selected for the questions of that section, but this could slow down the process. Any other ideas? The error checking subsystem. What else can I do to minimize or to check human typos in the multiple choice questions? Is this a solvable problem? is there some statistical methodology to check values that were entered by the users are the same from the hand filled forms? For example, let's suppose the survey has 5 questions, and each has 4 options. Let's say I have n survey forms filled in paper by interviewers, and they're ready to be entered in the software, then how to minimize the accidental differences that can have the manual transcription of the n surveys, without having to double check everything in the 5 questions of the n surveys? My first suggestion is that at the end of the processing of all the hand filled forms, the software could choose some forms randomly to make a double check of the responses in a few instances, but on what criteria can I make this selection? This validation would be enough to cover everything in a significant way? The actual survey is nation level and it has 56 pages with over 200 questions in total, so it will be a lot of hand written pages by many people, and the intention is to reduce the likelihood of errors and to optimize speed in the data entry process. The surveys must filled in paper first, given the complications of taking laptops or handhelds with the interviewers.

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• Ideas for designing an automated content tagging system needed

  - by Benjamin Smith

  I am currently designing a website that amongst other is required to display and organise small amounts of text content (mainly quotes, article stubs, etc.). I currently have a database with 250,000+ items and need to come up with a method of tagging each item with relevant tags which will eventually allow for easy searching/browsing of the content for users. A very simplistic idea I have (and one that I believe is employed by some sites that I have been looking to for inspiration (http://www.brainyquote.com/quotes/topics.html)), is to simply search the database for certain words or phrases and use these words as tags for the content. This can easily be extended so that if for example a user wanted to show all items with a theme of love then I would just return a list of items with words and phrases relating to this theme. This would not be hard to implement but does not provide very good results. For example if I were to search for the month 'May' in the database with the aim of then classifying the items returned as realting to the topic of Spring then I would get back all occurrences of the word May, regardless of the semantic meaning. Another shortcoming of this method is that I believe it would be quite hard to automate the process to any large scale. What I really require is a library that can take an item, break it down and analyse the semantic meaning and also return a list of tags that would correctly classify the item. I know this is a lot to ask and I have a feeling I will end up reverting to the aforementioned method but I just thought I should ask if anyone knew of any pre-existing solution. I think that as the items in the database are short then it is probably quite a hard task to analyse any meaning from them however I may be mistaken. Another path to possibly go down would be to use something like amazon turk to outsource the task which may produce good results but would be expensive. Eventually I would like users to be able to (and want to!) tag content and to vote for the most relevant tags, possibly using a gameification mechanic as motivation however this is some way down the line. A temporary fix may be the best thing if this were the route I decided to go down as I could use the rough results I got as the starting point for a more in depth solution. If you've read this far, thanks for sticking with me, I know I'm spitballing but any input would be really helpful. Thanks.

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• Pointer-based binary heap implementation

  - by Derek Chiang

  Is it even possible to implement a binary heap using pointers rather than an array? I have searched around the internet (including SO) and no answer can be found. The main problem here is that, how do you keep track of the last pointer? When you insert X into the heap, you place X at the last pointer and then bubble it up. Now, where does the last pointer point to? And also, what happens when you want to remove the root? You exchange the root with the last element, and then bubble the new root down. Now, how do you know what's the new "last element" that you need when you remove root again?

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• Convert arbitrary size of byte[] to BigInteger[] and then safely convert back to exactly the same by

  - by PatlaDJ

  I believe conversion exactly to BigInteger[] would be optimal in my case. Anyone had done or found this written in Java and willing to share? So imagine I have arbitrary size byte[] = {0xff,0x3e,0x12,0x45,0x1d,0x11,0x2a,0x80,0x81,0x45,0x1d,0x11,0x2a,0x80,0x81} How do I convert it to array of BigInteger's and then be able to recover it back the original byte array safely? ty in advance.

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• How can I test if a point lies within a 3d shape with its surface defined by a point cloud?

  - by Ben

  Hi I have a collection of points which describe the surface of a shape that should be roughly spherical, and I need a method with which to determine if any other given point lies within this shape. I've previously been approximating the shape as an exact sphere, but this has proven too inaccurate and I need a more accurate method. Simplicity and speed is favourable over complete accuracy, a good approximation will suffice. I've come across techniques for converting a point cloud to a 3d mesh, but most things I have found have been very complicated, and I am looking for something as simple as possible. Any ideas? Many thanks, Ben.

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• incremental way of counting quantiles for large set of data

  - by Gacek

  I need to count the quantiles for a large set of data. Let's assume we can get the data only through some portions (i.e. one row of a large matrix). To count the Q3 quantile one need to get all the portions of the data and store it somewhere, then sort it and count the quantile: List<double> allData = new List<double>(); foreach(var row in matrix) // this is only example. In fact the portions of data are not rows of some matrix { allData.AddRange(row); } allData.Sort(); double p = 0.75*allData.Count; int idQ3 = (int)Math.Ceiling(p) - 1; double Q3 = allData[idQ3]; Now, I would like to find a way of counting this without storing the data in some separate variable. The best solution would be to count some parameters od mid-results for first row and then adjust it step by step for next rows. Note: These datasets are really big (ca 5000 elements in each row) The Q3 can be estimated, it doesn't have to be an exact value. I call the portions of data "rows", but they can have different leghts! Usually it varies not so much (+/- few hundred samples) but it varies! This question is similar to this one: http://stackoverflow.com/questions/1058813/on-line-iterator-algorithms-for-estimating-statistical-median-mode-skewness But I need to count quantiles. ALso there are few articles in this topic, i.e.: http://web.cs.wpi.edu/~hofri/medsel.pdf http://portal.acm.org/citation.cfm?id=347195&dl But before I would try to implement these, I wanted to ask you if there are maybe any other, qucker ways of counting the 0.25/0.75 quantiles?

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• How to reverse a number as an integer and not as a string?

  - by Pritam

  I came across a question "How can one reverse a number as an integer and not as a string?" Could anyone please help me to find out the answer.

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• question about api functions

  - by davit-datuashvili

  i have question we have API functions in java can user create it's own function and add to his java IDE? for example i am using netbeans can i create my own function add to netbean IDE?let say create binary function or something else thanks

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• Finding the largest subtree in a BST

  - by rakeshr

  Given a binary tree, I want to find out the largest subtree which is a BST in it. Naive approach: I have a naive approach in mind where I visit every node of the tree and pass this node to a isBST function. I will also keep track of the number of nodes in a sub-tree if it is a BST. Is there a better approach than this ?

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• Solving simultaneous equations

  - by Milo

  Here is my problem: Given x, y, z and ratio where z is known and ratio is known and is a float representing a relative value, I need to find x and y. I know that: x / y == ratio y - x == z What I'm trying to do is make my own scroll pane and I'm figuring out the scrollbar parameters. So for example, If the scrollbar must be able to scroll 100 values (z) and the thumb must consume 80% of the bar (ratio = 0.8) then x would be 400 and y would be 500. Thanks

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• hi question about mathematics

  - by davit-datuashvili

  hi i have one question i know site mathoverflow.com and have posted question but unfortunately no one give me answer if i post here can anybody help me? it is not homework because i know somebody will say it is homework what u have tried but this is not so i dont know how solve please if it is possible i will post here ok?

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• Revisions: algorithm and data structure

  - by SODA

  Hi, I need ideas for structuring and processing data with revisions. For example, I have a database of objects (e.g. cars). Each object has a number of properties, which can be arbitrary, so there's no a set schema to describe these objects. These objects are probably saved as key-value pairs. Now I need to change property of an object. I don't want to completely rewrite it - I want to be able to go back and see history of changes to these properties, that's why I want to add new property and keep the old one (so I guess a timestamp would do the job of telling which property is the latest). At the same time I want to be able to get info about any object in a snap, with only latest versions of each of the properties. Any ideas what would be the best approach? At least please point me in the right direction. Thanks!

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• What is the difference between tree depth and height?

  - by Gabriel Šcerbák

  This is a simple question from algorithms theory. The difference between them is that in one case you count number of nodes and in other number of edges on the shortest path between root and concrete node. Which is which?

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• question bitonic sequence

  - by davit-datuashvili

  A sequence is bitonic if it monotonically increases and then monotonically de- creases, or if it can be circularly shifted to monotonically increase and then monotonically decrease. For example the sequences 1, 4, 6, 8, 3, -2 , 9, 2, -4, -10, -5 , and 1, 2, 3, 4 are bitonic, but 1, 3, 12, 4, 2, 10 is not bitonic. please help me to determine if given sequence is bitonic?

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• Clamping a vector to a minimum and maximum?

  - by user146780

  I came accross this: t = Clamp(t/d, 0, 1) but I'm not sure how to perform this operation on a vector. What are the steps to clamp a vector if one was writing their own vector implementation? Thanks clamp clamping a vector to a minimum and a maximum ex: pc = # the point you are coloring now p0 = # start point p1 = # end point v = p1 - p0 d = Length(v) v = Normalize(v) # or Scale(v, 1/d) v0 = pc - p0 t = Dot(v0, v) t = Clamp(t/d, 0, 1) color = (start_color * t) + (end_color * (1 - t))

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• Interview question: How do I detect a loop in this linked list?

  - by jjujuma

  Say you have a linked list structure in Java. It's made up of Nodes: class Node { Node next; // some user data } and each Node points to the next node, except for the last Node, which has null for next. Say there is a possibility that the list can contain a loop - i.e. the final Node, instead of having a null, has a reference to one of the nodes in the list which came before it. What's the best way of writing boolean hasLoop(Node first) which would return true if the given Node is the first of a list with a loop, and false otherwise? How could you write so that it takes a constant amount of space and a reasonable amount of time? Here's a picture of what a list with a loop looks like: Node->Node->Node->Node->Node->Node--\ \ | ----------------

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• How to find the longest palindrome in a given string?

  - by Hun1Ahpu

  I know how to do this in O(n^2). But it seems like there exist a better solution. I've found this, and there is a link to O(n) answer, but it's written in Haskell and not clear for me. It would be great to get an answer in c# or similar.

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• Way to store a large dictionary with low memory footprint + fast lookups (on Android)

  - by BobbyJim

  I'm developing an android word game app that needs a large (~250,000 word dictionary) available. I need: reasonably fast look ups e.g. constant time preferable, need to do maybe 200 lookups a second on occasion to solve a word puzzle and maybe 20 lookups within 0.2 second more often to check words the user just spelled. EDIT: Lookups are typically asking "Is in the dictionary?". I'd like to support up to two wildcards in the word as well, but this is easy enough by just generating all possible letters the wildcards could have been and checking the generated words (i.e. 26 * 26 lookups for a word with two wildcards). as it's a mobile app, using as little memory as possible and requiring only a small initial download for the dictionary data is top priority. My first naive attempts used Java's HashMap class, which caused an out of memory exception. I've looked into using the SQL lite databases available on android, but this seems like overkill. What's a good way to do what I need?

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• Dot Game and Dynamic Programming

  - by Albert Diego

  I'm trying to solve a variant of the dot game with dynamic programming. The regular dot game is played with a line of dots. Each player takes either one or two dots at their respective end of the line and the person who is left with no dots to take wins. In this version of the game, each dot has a different value. Each player takes alternate turns and takes either dot at either end of the line. I want to come up with a way to use dynamic programming to find the max amount that the first player is guaranteed to win. I'm having problems grasping my head around this and trying to write a recurrence for the solution. Any help is appreciated, thanks!

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