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  • Using local classes with STL algorithms

    - by David Rodríguez - dribeas
    I have always wondered why you cannot use locally defined classes as predicates to STL algorithms. In the question: Approaching STL algorithms, lambda, local classes and other approaches, BubbaT mentions says that 'Since the C++ standard forbids local types to be used as arguments' Example code: int main() { int array[] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }; std::vector<int> v( array, array+10 ); struct pair : public std::unary_function<int,bool> { bool operator()( int x ) { return !( x % 2 ); } }; std::remove_if( v.begin(), v.end(), pair() ); // error } Does anyone know where in the standard is the restriction? What is the rationale for disallowing local types?

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  • Number Random Shuffle

    - by stjowa
    Hi, I need a Javascript random number shuffler for my website. Seems simple, but I can not figure out how to do it. Can anyone help me out? I have the following array of numbers: 1 2 3 4 5 6 7 8 9 I would like to be able to have these numbers shuffled randomly. Like the following: 3 6 4 2 9 5 1 8 7 or 4 1 7 3 5 9 2 6 8 So, specifically, I would like a function that takes in an array of numbers (1 - n) and then returns that same array of numbers - shuffled randomly with different calls to the function. Maybe a noob function, but can't seem to figure it out. Thanks! NOTE: Thanks for the clarification on "Shuffle". Have found a lot more online about this with that term.

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  • Why "Algorithms" and "Data Structures" are treated as separate disciplines?

    - by Pavel Shved
    This question was the last straw; and I've been wondering for a long time about it, Why do people think about "Algorithms" and "Data structures" as about something that can be separated from each other? I see a lot of evidence that they're separated in programmers' minds. they request "Data Structures & Algorithms" books they refer to "Data Structures" and "Algorithms" as separate university courses they "know Algorithms", but are "weak in Data Structures" (can't find the link, sorry). etc. In my opinion "Data Structures" are algorithms, since the concept of "Data Structure" is about Algorithms to operate data that go in and out of the structures. But the opinion seems not a mainstream. What do I miss?

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  • .NET Geometry Library

    - by dewald
    Does anyone know of a good (efficient, nice API, etc.) geometry open source library for .NET? Some of the operations needed: Data Structures Vectors (2D and 3D with floats and doubles) Lines (2D and 3D) Rectangles / Squares / Cubes / Boxes Spheres / Circles N-Sided Polygon Matrices (floats and doubles) Algorithms Intersection calculations Area / Volume calculations

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  • Most efficient sorting of calculation on DataTable column calculation

    - by byte
    Lets say you have a DataTable that has columns of "id", "cost", "qty": DataTable dt = new DataTable(); dt.Columns.Add("id", typeof(int)); dt.Columns.Add("cost", typeof(double)); dt.Columns.Add("qty", typeof(int)); And it's keyed on "id": dt.PrimaryKey = new DataColumn[1] { dt.Columns["id"] }; Now what we are interested in is the cost per quantity. So, in other words if you had a row of: id | cost | qty ---------------- 42 | 10.00 | 2 The cost per quantity is 5.00. My question then is, given the preceeding table, assume it's constructed with many thousands of rows, and you're interested in the top 3 cost per quantity rows. The information needed is the id, cost per quantity. You cannot use LINQ. In SQL it would be trivial; how BEST (most efficiently) would you accomplish it in C# without LINQ?

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  • Why is my logic not working correctly for SPOJ TOPOSORT?

    - by Kavish Dwivedi
    The given problem is http://www.spoj.com/problems/TOPOSORT/ The output format is particularly important as : Print "Sandro fails." if Sandro cannot complete all his duties on the list. If there is a solution print the correct ordering, the jobs to be done separated by a whitespace. If there are multiple solutions print the one, whose first number is smallest, if there are still multiple solutions, print the one whose second number is smallest, and so on. What I am doing is simply doing dfs by reversing the edges i.e if job A finishes before job B, there is a directed edge from B to A . I am maintaining the order by sorting the adjacency list I created and storing the nodes which don't have any constraints separately so as to print them later in correct order . There are two flag arrays used , one for marking discovered node and one for marking the node whose all neighbors have been explored. Now my solution is http://www.ideone.com/QCUmKY (the important function is the visit funtion ) and its giving WA after running correct for 10 cases so its really hard to figure out where am I doing it wrong since it runs for all of the test cases which I have done by hand.

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  • Substring and its reverse in a string

    - by christa
    My professor was talking about this in a Dynamic programming class and asked us to think over it. She gave us some examples as well. Given a string, we were to find the longest continuous subsequence whose reverse is also a subsequence present in the given string. Example: INPUT: pqrstuvtsrv OUTPUT: i=3, k=2 rst -> tsr (rst found first at i=3 and for 2 more positions) INPUT: mpqrsrqp OUTPUT: i=2, k=6 pqrsrqp in reverse INPUT: mmpqssss OUTPUT: i=5, k=3 I thought of putting the string and its reverse into 2 different arrays and comparing character by character. But I'm sure this is not the best way to do it. Any suggestions as to what could be the most efficient ?

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  • Calculate shortest path through a grocery store

    - by Bart
    Hi, I'm trying to find a way to find the shortest path through a grocery store, visiting a list of locations (shopping list). The path should start at a specified startposition and can end at multiple endpositions (there are multiple checkout counters). Also, I have some predefined constraints on the path, such as "item x on the shopping list needs to be the last, second last, or third last item on the path". There is a function that will return true or false for a given path. Finally, this needs to be calculated with limited cpu power (on a smartphone) and within a second or so. If this isn't possible, then an approximation to the optimal path is also ok. Is this possible? So far I think I need to start by calculating the distance between every item on the list using something like A* or Dijkstra's. After that, should I treat it like the travelling salesman problem? Because in my problem there is a specified startnode, specified endnodes, and some constraints, which are not in the travelling salesman problem. Any help would be appreciated :)

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  • bug/error in basis set path algorithm i can't figure out

    - by Roy McAvoy
    The following looks through a 2d array to find basis set paths. It is supposed to print out the individual paths but not repeat any and end when all paths are found. It however doesn't stop at the last path and has a bug in it somewhere in which the following happens: It goes halfway through the path and then goes to zero and ends the path for some reason. For example the table is filled with the following: all 0s, except for [1][2], [1][3], [2][4], [2][5], [3][5], [4][6], [5][6], [6][0] which all have a 1 in them. The desired paths are P1: 1 2 4 6 0 P2: 1 3 5 6 0 P3: 1 2 5 6 0. The output I get when i run the program is 12460 13560 1250 124 Any and all help on this is much appreciated, this is just the function that scans through the array looking for paths, I can add the entire program if that would be helpful. Thanks.. void find_path(int map[][MAX], int x){ int path =0; int m=1; int blah=0; bool path_found = false; do { for(int n=0;n<(x+1);n++){ if(map[m][n]==-1){ blah=(n+1); if(blah<(x+1)){ for(blah;blah<(x+1);blah++){ if(map[m][blah]==1){ map[m][blah]=-1; path=m; path_found = true; cout<<path; m=blah; n=0; } } } else{ path=m; path_found=false; cout<<path; m=n; if(m==0){ path=0; cout<<path<<endl; m=1; path_found=false; } } } else if(map[m][n]==1){ map[m][n]=-1; path=m; path_found = true; cout<<path; m=n; if(m==0){ path=0; cout<<path<<endl; m=1; path_found=false; } } } } while(m<(x+1) && path_found); }

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  • Rotate array clockwise

    - by user69514
    I have a two dimensional array that I need to rotate 90 degrees clockwise, however I keep getting arrayindexoutofbounds... public int[][] rorateArray(int[][] arr){ //first change the dimensions vertical length for horizontal length //and viceversa int[][] newArray = new int[arr[0].length][arr.length]; //invert values 90 degrees clockwise by starting from button of //array to top and from left to right int ii = 0; int jj = 0; for(int i=0; i<arr[0].length; i++){ for(int j=arr.length-1; j>=0; j--){ newArray[ii][jj] = arr[i][j]; jj++; } ii++; } return newArray; }

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  • tfidf, am I understanding it right?

    - by alskndalsnd
    Hey everyone, I am interested in doing some document clustering, and right now I am considering using TF-IDF for this. If I am not wrong, TFIDF is particularly used for evaluating the relevance of a document given a query. If I do not have a particular query, how can I apply tfidf to clustering?

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  • Most efficent way to create all possible combinations of four lists in Python?

    - by Baresi
    I have four different lists. headers, descriptions, short_descriptions and misc. I want to combine these into all the possible ways to print out: header\n description\n short_description\n misc like if i had (i'm skipping short_description and misc in this example for obvious reasons) headers = ['Hello there', 'Hi there!'] description = ['I like pie', 'Ho ho ho'] ... I want it to print out like: Hello there I like pie ... Hello there Ho ho ho ... Hi there! I like pie ... Hi there! Ho ho ho ... What would you say is the best/cleanest/most efficent way to do this? Is for-nesting the only way to go?

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  • Find all substrings of a string - StringIndexOutOfBoundsException

    - by nazar_art
    I created class Word. Word has a constructor that takes a string argument and one method getSubstrings which returns a String containing all substring of word, sorted by length. For example, if the user provides the input "rum", the method returns a string that will print like this: r u m ru um rum I want to concatenate the substrings in a String, separating them with a newline ("\n"). Then return the string. Code: public class Word { String word; public Word(String word) { this.word = word; } /** * Gets all the substrings of this Word. * @return all substrings of this Word separated by newline */ public String getSubstrings() { String str = ""; int i, j; for (i = 0; i < word.length(); i++) { for (j = 0; j < word.length(); j++) { str = word.substring(i, i + j); str += "\n"; } } return str; } But it throws exception: java.lang.StringIndexOutOfBoundsException: String index out of range: -1 at java.lang.String.substring(String.java:1911) I stuck at this point. Maybe, you have other suggestions according this method signature public String getSubstrings(). How to solve this issue?

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  • LZMA for Delphi

    - by SaCi
    I got a LZMA library on 7-zip site, but that didn't worked. I'm not using files, just stream. And for some why the library on 7-zip site just write the header on the stream but not compress the stream. Some one faced the some problem ? Have some example ? Know other LZMA library for Delphi ? Tks

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  • What is better, a STL list or a STL Map for 20 entries, considering order of insertion is as importa

    - by Abhijeet
    I have the following scenario.The implementation is required for a real time application. 1)I need to store at max 20 entries in a container(STL Map, STL List etc). 2)If a new entry comes and 20 entries are already present i have to overwrite the oldest entry with the new entry. Considering point 2, i feel if the container is full (Max 20 entries) 'list' is the best bet as i can always remove the first entry in the list and add the new one at last (push_back). However, search won't be as efficient. For only 20 entries, does it really make a big difference in terms of searching efficiency if i use a list in place of a map? Also considering the cost of insertion in map i feel i should go for a list? Could you please tell what is a better bet for me ?

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  • Mysql results sorted by list which is unique for each user

    - by ADAM
    Ive got a table of thousands of products and 50 or so authenticated users. These users all show the products on their own web sites and they all require the ability to have them ordered differently. Im guesing i need some kind of seperate table for the orders which contains the product_id, user_id and order column? How do i do this the most efficiently in mysql so as to be very fast, and not slow down if i get millions of products in the database. Is it even wise to do it in mysql or should i be using some kind of other index like solr/lucene? My Product table is called "products" My User table is called "users" A good example of the functionality i need is google search where you can order/supress the results if you are logged in. edit: the product results will be paginated and the users have the authority to edit the products, so its not just ready only

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  • How to determine visibility in 2D

    - by Jack
    Hello, I'm developing an AI sandbox and I would like to calculate what every living entity can see. The rule is to simply hide what's behind the edges of the shapes from the point of view of the entity. The image clarifies everything: I need it either as an input to the artificial intelligence either graphically, to show it for a specific entity while it moves.. Any cool ideas?

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  • How to find two most distant points?

    - by depesz
    This is a question that I was asked on a job interview some time ago. And I still can't figure out sensible answer. Question is: you are given set of points (x,y). Find 2 most distant points. Distant from each other. For example, for points: (0,0), (1,1), (-8, 5) - the most distant are: (1,1) and (-8,5) because the distance between them is larger from both (0,0)-(1,1) and (0,0)-(-8,5). The obvious approach is to calculate all distances between all points, and find maximum. The problem is that it is O(n^2), which makes it prohibitively expensive for large datasets. There is approach with first tracking points that are on the boundary, and then calculating distances for them, on the premise that there will be less points on boundary than "inside", but it's still expensive, and will fail in worst case scenario. Tried to search the web, but didn't find any sensible answer - although this might be simply my lack of search skills.

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  • Word Jumble Algorithm

    - by MasterMax1313
    Given a word jumble (i.e. ofbaor), what would be an approach to unscramble the letters to create a real word (i.e. foobar)? I could see this having a couple of approaches, and I think I know how I'd do it in .NET, but I curious to see what some other solutions look like (always happy to see if my solution is optimal or not). This isn't homework or anything like that, I just saw a word jumble in the local comics section of the paper (yes, good ol' fashioned newsprint), and the engineer in me started thinking.

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  • how to manage a "resource" array efficiently

    - by Haiyuan Zhang
    The senario of my question is that one need to use a fixed size of array to keep track of certain number of "objects" . The object here can be as simply as a integer or as complex as very fancy data structure. And "keep track" here means to allocate one object when other part of the app need one instance of object and recyle it for future allocation when one instance of the object is returned .Finally ,let me use c++ to put my problme in a more descriptive way . #define MAX 65535 /* 65535 just indicate that many items should be handled . performance demanding! */ typedef struct { int item ; }Item_t; Item_t items[MAX] ; class itemManager { private : /* up to you.... */ public : int get() ; /* get one index to a free Item_t in items */ bool put(int index) ; /* recyle one Item_t indicate by one index in items */ } how will you implement the two public functions of itemManager ? it's up to you to add any private member .

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