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  • Result of Long Positive Integers & Search and element in array..

    - by AGeek
    Hi, I have two Questions for which I cannot find answers by googling, but I find these questions very important for preparation.. Kindly explain only the logic, I will be able to code. In Search of Efficient Logic..... in terms of Memory and Time. WAP to add two long positive integers. What Data structure / data type we can use to store the numbers and result. What is the best way to search an element from an array in shortest time. Size of the array could be large enough, and any elements could be stored in the array(i.e. no range). Thanks.

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  • Dictionaries with more than one key per value in Python

    - by nickname
    I am attempting to create a nice interface to access a data set where each value has several possible keys. For example, suppose that I have both a number and a name for each value in the data set. I want to be able to access each value using either the number OR the name. I have considered several possible implementations: Using two separate dictionaries, one for the data values organized by number, and one for the data values organized by name. Simply assigning two keys to the same value in a dictionary. Creating dictionaries mapping each name to the corresponding number, and vice versa Attempting to create a hash function that maps each name to a number, etc. (related to the above) Creating an object to encapsulate all three pieces of data, then using one key to map dictionary keys to the objects and simply searching the dictionary to map the other key to the object. None of these seem ideal. The first seems ugly and unmaintainable. The second also seems fragile. The third/fourth seem plausible, but seem to require either much manual specification or an overly complex implementation. Finally, the fifth loses constant-time performance for one of the lookups. In C/C++, I believe that I would use pointers to reference the same piece of data from different keys. I know that the problem is rather similar to a database lookup problem by a non-key column, however, I would like (if possible), to maintain the approximate O(1) performance of Python dictionaries. What is the most Pythonic way to achieve this data structure?

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  • python dictionary with constant value-type

    - by s.kap
    hi there, I bumped into a case where I need a big (=huge) python dictionary, which turned to be quite memory-consuming. However, since all of the values are of a single type (long) - as well as the keys, I figured I can use python (or numpy, doesn't really matter) array for the values ; and wrap the needed interface (in: x ; out: d[x]) with an object which actually uses these arrays for the keys and values storage. I can use a index-conversion object (input -- index, of 1..n, where n is the different-values counter), and return array[index]. I can elaborate on some techniques of how to implement such an indexing-methods with reasonable memory requirement, it works and even pretty good. However, I wonder if there is such a data-structure-object already exists (in python, or wrapped to python from C/++), in any package (I checked collections, and some Google searches). Any comment will be welcome, thanks.

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  • Is there a good collection library for C-language?

    - by matti
    We have to maintain and even develop C-code of our legacy system. Is there good collection library that would support Java/C# (new versions) style collections. Hashtable, HashSet, etc. Of course without objects, but with structs. The HashTable key limitations to "strings" and ints is not a problem. It wouldn't be bad if it's free even for commercial use. I'm back to C from C# and I must say i'm depressed using our own libraries and the language in general. We're using VS2005 and MS C-compiler if that has nothing to do with anything. Thanks & BR -Matti

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  • How to create wordpress-like option table and get values for each row?

    - by Nacho
    Hi guys. I'm looking to create an options table in my db that makes every record a system option, so I can work with a little number of fields. My db has the following structure: 3 columns named id, name, and value The following data is inserted as an example: +--+-----------+--------------------------+ |id|name |value | +--+-----------+--------------------------+ | 1|uri |www.example.com | | 2|sitename |Working it out | | 3|base_folder|/folder1/folder2/ | | 4|slogan |Just a slogan for the site| +--+-----------+--------------------------+ That way I can include a large number of customizable system options very easily. The problem is that I don't know how to retrieve them. How do I get the value of uri and store it as a var? And better yet, how do I get, for exmaple, values of id 1 and 4 only without making a query each time? (I assume multiple queries are useless and a pretty ugly method.) I know the question is pretty basic but I'm lost here. I'd really appreciate your answer!

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  • DB Architecture : Linking to intersection or to main tables?

    - by Jean-Nicolas
    Hi, I'm creating fantasy football system on my website but i'm very confuse about how I should link some of my table. Tables The main table is Pool which have all the info about the ruling of the fantasy draft. A standard table User, which contains the usual stuff. Intersection table called pools_users which contains id,pool_id,user_id because a user could be in more than one pool, and a pool contains more than 1 user. The problem Table Selections = that's the table that is causing problem. That's the selection that the user choose for his pool. This is related to the Player table but thats not relevant for this problem. Should I link this table to the table Pools_users or should I link it with both main table Pool and User. This table contains id,pool_id,user_id,player_id,... What is the best way link my tables? When I want to retrieve my data, I normally want the information to be divided BY users. "This user have those selections, this one those selections, etc).

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  • 0/1 Knapsack with irrational weights

    - by user356106
    Consider the 0/1 knapsack problem. The standard Dynamic Programming algorithm applies only when the capacity as well as the weights to fill the knapsack with are integers/ rational numbers. What do you do when the capacity/weights are irrational? The issue is that we can't memoize like we do for integer weights because we may need potentially infinite decimal places for irrational weights - leading to an infinitely large number of columns for the Dynamic Programming Table . Is there any standard method for solving this? Any comments on the complexity of this problem? Any heuristics? What about associated recurrences like (for example): f(x)=1, for x< sqrt(2) f(x)=f(x-sqrt(2))+sqrt(3)

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  • Extending existing data structure in Scala.

    - by Lukasz Lew
    I have a normal tree defined in Scala. sealed abstract class Tree case class Node (...) extends Tree case class Leaf (...) extends Tree Now I want to add a member variable to all nodes and leaves in the tree. Is it possible with extend keyword or do I have to modify the tree classes by adding [T]?

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  • Item in multiple lists

    - by Evan Teran
    So I have some legacy code which I would love to use more modern techniques. But I fear that given the way that things are designed, it is a non-option. The core issue is that often a node is in more than one list at a time. Something like this: struct T { T *next_1; T *prev_1; T *next_2; T *prev_2; int value; }; this allows the core have a single object of type T be allocated and inserted into 2 doubly linked lists, nice and efficient. Obviously I could just have 2 std::list<T*>'s and just insert the object into both...but there is one thing which would be way less efficient...removal. Often the code needs to "destroy" an object of type T and this includes removing the element from all lists. This is nice because given a T* the code can remove that object from all lists it exists in. With something like a std::list I would need to search for the object to get an iterator, then remove that (I can't just pass around an iterator because it is in several lists). Is there a nice c++-ish solution to this, or is the manually rolled way the best way? I have a feeling the manually rolled way is the answer, but I figured I'd ask.

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  • What's beyond c,c++ and data structure?

    - by sagacious
    I have learnt c and c++ programming languages.i have learnt data structure too. Now i'm confused what to do next?my aim is to be a good programmer. i want to go deeper into the field of programming and making the practical applications of what i have learnt. So,the question takes the form-what to do next?Or is there any site where i can see advantage of every language with it's features? sorry,if there's any language error and thanks in advance.

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  • Appropriate data structure for a buffer of the packets

    - by psihodelia
    How to implement a buffer of the packets where each packet is of the form: typedef struct{ int32 IP; //4-byte IP-address int16 ID; //unique sequence id }t_Packet; What should be the most appropriate data structure which: (1) allows to collect at least 8000 such packets (fast Insert and Delete operations) (2) allows very fast filtering using IP address, so that only packets with given IP will be selected (3) allows very fast find operation using ID as a key (4) allows very fast (2), then (3) within filtered results ? RAM size does matter, e.g. no huge lookup table is possible to use.

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  • Rowwise iteration of a dictionay object

    - by mono
    I have a dictionary object like: Dictionary<string, HashSet<int>> dict = new Dictionary<string, HashSet<int>>(); dict.Add("foo", new HashSet<int>() { 15,12,16,18}); dict.Add("boo", new HashSet<int>() { 16,47,45,21 }); I have to print in such a way such that result would be as following at each iteration: It1: foo boo //only the key in a row It2: 15 16 It3: 16 47 Can anyone help me to achieve this. Thanks.

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  • Store address dynamic array in c

    - by user280642
    I'm trying to save the address of a dynamic array index. struct sstor *dlist; struct node *q; q->item = &(dlist->item[(dlist->sz)-1]); // Problem? This is my node struct node { char **item; struct node *next; struct node *prev; }; This is my array struct sstor { int sz; int maxsz; char item[][1024]; }; I'm still new to pointers. The line below gives the error: assignment from incompatible pointer type q->item = &(dlist->item[(dlist->sz)-1]);

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  • c++ templates and inheritance

    - by Armen Ablak
    Hey, I'm experiencing some problems with breaking my code to reusable parts using templates and inheritance. I'd like to achieve that my tree class and avltree class use the same node class and that avltree class inherits some methods from the tree class and adds some specific ones. So I came up with the code below. Compiler throws an error in tree.h as marked below and I don't really know how to overcome this. Any help appreciated! :) node.h: #ifndef NODE_H #define NODE_H #include "tree.h" template <class T> class node { T data; ... node() ... friend class tree<T>; }; #endif tree.h #ifndef DREVO_H #define DREVO_H #include "node.h" template <class T> class tree { public: //signatures tree(); ... void insert(const T&); private: node<T> *root; //missing type specifier - int assumed. Note: C++ does not support default-int }; //implementations #endif avl.h #ifndef AVL_H #define AVL_H #include "tree.h" #include "node.h" template <class T> class avl: public tree<T> { public: //specific int findMin() const; ... protected: void rotateLeft(node<T> *)const; private: node<T> *root; }; #endif avl.cpp (I tried separating headers from implementation, it worked before I started to combine avl code with tree code) #include "drevo" #include "avl.h" #include "vozlisce.h" template class avl<int>; //I know that only avl with int can be used like this, but currently this is doesn't matter :) //implementations ...

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  • The C vs. C++ way

    - by amc
    Hi, So I have to write a program that will iterate through an image and record the pixel locations corresponding to each color pixel that appears in it. For example, given http://www.socuteurl.com/fishywishykissy I need to find the coordinates of all yellow, purple, dark pink, etc pixels. In C++ I would use a hash table to do this. I would iterate through the image, check each pixel's value, look up that value and either add to a vector of pixel coordinates if it were found or add a new entry to the table if the value were not already there. The problem is that I may need to write this program in pure C instead of C++. How would I go about doing this in C? I feel like implementing a hash table would be pretty obnoxious and error-prone: should I avoid doing that? I'm pretty inexperienced with C and have a fair amount of C++ experience, if that matters. Thanks.

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  • Python what's the data structure for triple data

    - by Paul
    I've got a set of data that has three attributes, say A, B, and C, where A is kind of the index (i.e., A is used to look up the other two attributes.) What would be the best data structure for such data? I used two dictionaries, with A as the index of each. However, there's key errors when the query to the data doesn't match any instance of A.

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  • C++ priority queue structure userd ?

    - by John Retallack
    While searching for some functions in C++ STL documentation I read that push and pop for priority queues needs constant time. "Constant (in the priority_queue). Although notice that push_heap operates in logarithmic time." My question is what kind of data structure is used to mantain a priority queue with O(1) for push and pop ?

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  • C++ stl collections or linked lists

    - by Lucas
    I'm developing a OpenGL based simulation in C++. I'm optmizing my code now and i see throughout the code the frequently use of std:list and std:vector. What is the more performatic: to continue using C++ stl data structs or a pointer based linked list? The main operation that involve std::list and std::vector is open a iterator and loop through all items in the data structs and apply some processing

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  • Sorted queue with dropping out elements

    - by ffriend
    I have a list of jobs and queue of workers waiting for these jobs. All the jobs are the same, but workers are different and sorted by their ability to perform the job. That is, first person can do this job best of all, second does it just a little bit worse and so on. Job is always assigned to the person with the highest skills from those who are free at that moment. When person is assigned a job, he drops out of the queue for some time. But when he is done, he gets back to his position. So, for example, at some moment in time worker queue looks like: [x, x, .83, x, .7, .63, .55, .54, .48, ...] where x's stand for missing workers and numbers show skill level of left workers. When there's a new job, it is assigned to 3rd worker as the one with highest skill of available workers. So next moment queue looks like: [x, x, x, x, .7, .63, .55, .54, .48, ...] Let's say, that at this moment worker #2 finishes his job and gets back to the list: [x, .91, x, x, .7, .63, .55, .54, .48, ...] I hope the process is completely clear now. My question is what algorithm and data structure to use to implement quick search and deletion of worker and insertion back to his position. For the moment the best approach I can see is to use Fibonacci heap that have amortized O(log n) for deleting minimal element (assigning job and deleting worker from queue) and O(1) for inserting him back, which is pretty good. But is there even better algorithm / data structure that possibly take into account the fact that elements are already sorted and only drop of the queue from time to time?

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