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  • How to calculate the state of a graph?

    - by zcb
    Given a graph G=(V,E), each node i is associated with 'Ci' number of objects. At each step, for every node i, the Ci objects will be taken away by the neighbors of i equally. After K steps, output the number of objects of the top five nodes which has the most objects. Some Constrains: |V|<10^5, |E|<2*10^5, K<10^7, Ci<1000 My current idea is: represent the transformation in each step with a matrix. This problem is converted to the calculation of the power of matrix. But this solution is much too slow considering |V| can be 10^5. Is there any faster way to do it?

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  • Length of Encrypted String

    - by Agnel Kurian
    I need to create a database column which will store a string encrypted using Triple DES. How do I determine the length of the encrypted string column? (Answers for algorithms other than Triple DES are also welcome.)

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  • question about siftdown operation on heap

    - by davit-datuashvili
    i have following pseudo code which execute siftdown operation on heap array suppose is x void siftdown(int n) pre heap(2,n) && n>=0 post heap(1,n) i=1; loop /*invariant heap(1,n) except perhaps between i and it's (0,1,or 2) children*/ c=2*i; if (c>n) break; // c is left child of i if (c+1)<=n /* c+1 is rigth child of i if (x[c+1]<x[c]) c++ /* c is lesser child of i if (x[i]<=x[c]) break; swap(c,i) i=c; i have wrote following code is it correct? public class siftdown{ public static void main(String[]args){ int c; int n=9; int a[]=new int[]{19,100,17,2,7,3,36,1,25}; int i=1; while (i<n){ c=2*i; if (c>n) break; //c is the left child of i if (c+1<=n) //c+1 ir rigth child of i if (a[c+1]<a[c]) c++; if (a[i]<=a[c]) break; int t=a[c]; a[c]=a[i]; a[i]=t; i=c; } for (int j=0;j<a.length;j++){ System.out.println(a[j]); } } } // result is 19 2 17 1 7 3 36 100 25

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  • public (static) swap() method vs. redundant (non-static) private ones...

    - by Helper Method
    I'm revisiting data structures and algorithms to refresh my knowledge and from time to time I stumble across this problem: Often, several data structures do need to swap some elements on the underlying array. So I implement the swap() method in ADT1, ADT2 as a private non-static method. The good thing is, being a private method I don't need to check on the parameters, the bad thing is redundancy. But if I put the swap() method in a helper class as a public static method, I need to check the indices every time for validity, making the swap call very unefficient when many swaps are done. So what should I do? Neglect the performance degragation, or write small but redundant code?

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  • algorithms that destruct and copy_construct

    - by FredOverflow
    I am currently building my own toy vector for fun, and I was wondering if there is something like the following in the current or next standard or in Boost? template<class T> void destruct(T* begin, T* end) { while (begin != end) { begin -> ~T(); ++begin; } } template<class T> T* copy_construct(T* begin, T* end, T* dst) { while (begin != end) { new(dst) T(*begin); ++begin; ++dst; } return dst; }

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  • Help to learn Image Search algorithm

    - by R Manu
    I am a beginner in image processing. I want to write an application in C++ or in C# for Searching an image in a list of images Searching for a particular feature (for e.g. face) in a list of images. Can anybody suggest where should I start from? What all should I learn before doing this? Where can I find the correct information regarding this?

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  • How would I use for_each to delete every value in an STL map?

    - by stusmith
    Suppose I have a STL map where the values are pointers, and I want to delete them all. How would I represent the following code, but making use of std::for_each? I'm happy for solutions to use Boost. for( stdext::hash_map<int, Foo *>::iterator ir = myMap.begin(); ir != myMap.end(); ++ir ) { delete ir->second; // delete all the (Foo *) values. } (I've found Boost's checked_delete, but I'm not sure how to apply that to the pair<int, Foo *> that the iterator represents). (Also, for the purposes of this question, ignore the fact that storing raw pointers that need deleting in an STL container isn't very sensible).

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  • Distributing players to tables

    - by IVlad
    Consider N = 4k players, k tables and a number of clans such that each member can belong to one clan. A clan can contain at most k players. We want to organize 3 rounds of a game such that, for each table that seats exactly 4 players, no 2 players sitting there are part of the same clan, and, for the later rounds, no 2 players sitting there have sat at the same table before. All players play all rounds. How can we do this efficiently if N can be about ~80 large? I thought of this: for each table T: repeat until 4 players have been seated at T: pick a random player X that is not currently seated anywhere if X has not sat at the same table as anyone currently at T AND X is not from the same clan as anyone currently at T seat X at T break I am not sure if this will always finish or if it can get stuck even if there is a valid assignment. Even if this works, is there a better way to do it?

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  • How to optimize this simple function which translates input bits into words?

    - by psihodelia
    I have written a function which reads an input buffer of bytes and produces an output buffer of words where every word can be either 0x0081 for each ON bit of the input buffer or 0x007F for each OFF bit. The length of the input buffer is given. Both arrays have enough physical place. I also have about 2Kbyte free RAM which I can use for lookup tables or so. Now, I found that this function is my bottleneck in a real time application. It will be called very frequently. Can you please suggest a way how to optimize this function? I see one possibility could be to use only one buffer and do in-place substitution. void inline BitsToWords(int8 *pc_BufIn, int16 *pw_BufOut, int32 BufInLen) { int32 i,j,z=0; for(i=0; i<BufInLen; i++) { for(j=0; j<8; j++, z++) { pw_BufOut[z] = ( ((pc_BufIn[i] >> (7-j))&0x01) == 1? 0x0081: 0x007f ); } } } Please do not offer any compiler specific or CPU/Hardware specific optimization, because it is a multi-platform project.

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  • please help me to implement such kind of sort

    - by davit-datuashvili
    hi i need to write sucj kind of sorting maybe it is similary to radix sort and also (this is not homework because i created it problem myself and please if anobody can help me) problem is like this suppose i have array int x[]=new int[]{4,5,3,2,1}; let write it into binary form 5 -0101 4- 0100 3-0011 2-0010 1-0001 i want to sort this elements by using bitwise operatos or check each bit and if less exchange it can anybody help me for example take 5 and 4 check first rightmost bit 0==0 so continue in the 1 index also 1==1 next the same 0=0 and last one 10 it means that first element is greater then second so exchange it please help me

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  • Find all A^x in a given range

    - by Austin Henley
    I need to find all monomials in the form AX that when evaluated falls within a range from m to n. It is safe to say that the base A is greater than 1, the power X is greater than 2, and only integers need to be used. For example, in the range 50 to 100, the solutions would be: 2^6 3^4 4^3 My first attempt to solve this was to brute force all combinations of A and X that make "sense." However this becomes too slow when used for very large numbers in a big range since these solutions are used in part of much more intensive processing. Here is the code: def monoSearch(min, max): base = 2 power = 3 while 1: while base**power < max: if base**power > min: print "Found " + repr(base) + "^" + repr(power) + " = " + repr(base**power) power = power + 1 base = base + 1 power = 3 if base**power > max: break I could remove one base**power by saving the value in a temporary variable but I don't think that would make a drastic effect. I also wondered if using logarithms would be better or if there was a closed form expression for this. I am open to any optimizations or alternatives to finding the solutions.

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  • Simple loop, which one I would get more performance and which one is recommended? defining a variable inside a loop or outside of it?

    - by Grego
    Variable outside of the loop int number = 0; for(int i = 0; i < 10000; i++){ number = 3 * i; printf("%d",number); } or Variable inside of the loop for(int i = 0; i < 10000; i++){ int number = 3 * i; printf("%d",number); } Which one is recommended and which one is better in performance? Edit: This is just an example to exhibit what I mean, All I wanna know is if defining a variable inside a loop and outside a loop means the same thing , or there's a difference.

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  • Fast matrix transposition in Python

    - by psihodelia
    Is there any fast method to make a transposition of a rectangular 2D matrix in Python (non-involving any library import).? Say, if I have an array X=[[1,2,3], [4,5,6]] I need an array Y which should be a transposed version of X, so Y=[[1,4],[2,5],[3,6]].

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  • Structure of Astar (A*) graph search data in C#

    - by Shawn Mclean
    How do you structure you graphs/nodes in a graph search class? I'm basically creating a NavMesh and need to generate the nodes from 1 polygon to the other. The edge that joins both polygons will be the node. I'll then run A* on these Nodes to calculate the shortest path. I just need to know how to structure my classes and their properties? I know for sure I wont need to create a fully blown undirected graph with nodes and edges.

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  • how to find out if a shape is passable

    - by jd
    I have a complex polygon (possibly concave) and a few of its edges marked as entry/exit points. there is a possibility that inside this polygon may lie one or more blockades of arbitrary shape. what approaches could I use to determine whether a path of certain width exists between a pair of entry/exit edges? having read through the question it looks like a homework type - it is not. I just wish to have a at least a few leads I could pursue, as this is new to me.

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  • question about function derivatives

    - by davit-datuashvili
    hi i have question for example i have some function int sumefunction(//parameters here let say int x){ return something let say x*x+2*x+3 or does not matter } i am interesting how find derivative of this function ?if i have int f(int x){ return sin(x); } after derivative it must return cos(x) thanks

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  • How to read arbitrary number of values using std::copy?

    - by Miro Kropacek
    Hi, I'm trying to code opposite action to this: std::ostream outs; // properly initialized of course std::set<int> my_set; // ditto outs << my_set.size(); std::copy( my_set.begin(), my_set.end(), std::ostream_iterator<int>( outs ) ); it should be something like this: std::istream ins; std::set<int>::size_type size; ins >> size; std::copy( std::istream_iterator<int>( ins ), std::istream_iterator<int>( ins ) ???, std::inserter( my_set, my_set.end() ) ); But I'm stuck with the 'end' iterator -- input interators can't use std::advance and neither I can use two streams with the same source... Is there any elegant way how to solve this? Of course I can use for loop, but maybe there's something nicer :)

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  • Generate a valid array key from an URL string in PHP

    - by John Riche
    I have a PHP array with some predefined values: $aArray = array( 0 => 'value0', 1 => 'value1' ); I need to create a function where the string input will always return the same, valid, array key so that when I call: GiveMeAKey('http://www.google.com'); // May return 0 or 1 I receive always the same key (I don't care which one) from the array. Obvisously I can't store the relationship in a database and the string passed to the GiveMeAKey method can be any URL. I wonder if there is a way of doing that ?

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  • Pointer mysteriously moves

    - by Armen Ablak
    Hi, I have this code for Node rotation and in a line which is marked something happens and I don't really know what and why :). //Test case 30 \ 16 / 29 RotationRight(node->mParent); //call template<class T> void SplayTree<T>::RotationRight(SplayNode<T> *&node) const { SplayNode<T> *left = node->mLeft; SplayNode<T> *parent = node->mParent; node->mLeft = left->mRight; if(left->HasRight()) left->mRight->mParent = node; left->mRight = node; //node in this line points to 0x00445198 {30} left->mParent = node->mParent; //and in this line it points to 0x00444fb8 {16} (node, not node->mParent) node->mParent = left; node = left; } Well, left-mParent points to node also, so I basically do node = node-mParent. The problem is I can't find a work around - how to unpin in from node and change it's pointing address without changing it's.

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  • question about in -place sort

    - by davit-datuashvili
    for example we have following array char data[]=new char[]{'A','S','O','R','T','I','N','G','E','X','A','M','P','L','E'}; and index array int a[]=new int[]{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14}: void insitu(char data[],int a[],N){ for (int i=0;i<N;i++) { char v=data[i]; int j,int k; for (k=i;a[k]!=i;k=a[j];a[j]=j) { j=k;data[k]=data[a[k]; } data[k]=v; a[k]=k; } i have question what is initialize value of j? when i run this code it asks me to initialize j and what should do? }

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