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  • Using static vs. member find method on a STL set?

    - by B Johnson
    I am using a set because, i want to use the quick look up property of a sorted container such as a set. I am wondering if I have to use the find member method to get the benefit of a sorted container, or can I also use the static find method in the STL algorithms? My hunch is that using the static version will use a linear search instead of a binary search like I want.

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  • How to choose an integer linear programming solver ?

    - by Cassie
    Hi all, I am newbie for integer linear programming. I plan to use a integer linear programming solver to solve my combinatorial optimization problem. I am more familiar with C++/object oriented programming on an IDE. Now I am using NetBeans with Cygwin to write my applications most of time. May I ask if there is an easy use ILP solver for me? Or it depends on the problem I want to solve ? I am trying to do some resources mapping optimization. Please let me know if any further information is required. Thank you very much, Cassie.

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  • Fastest way to write large STL vector to file using STL

    - by ljubak
    I have a large vector (10^9 elements) of chars, and I was wondering what is the fastest way to write such vector to a file. So far I've been using next code: vector<char> vs; // ... Fill vector with data ofstream outfile("nanocube.txt", ios::out | ios::binary); ostream_iterator<char> oi(outfile, '\0'); copy(vs.begin(), vs.end(), oi); For this code it takes approximately two minutes to write all data to file. The actual question is: "Can I make it faster using STL and how"?

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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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  • 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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  • STL map--> sort by value?

    - by Charlie Epps
    Hi I wonder how can I implement the STL map sorting by value. For example, I have a map m map<int, int>; m[1] = 10; m[2] = 5; m[4] = 6; m[6] = 1; and then.. I'd like to sort that with the m's value. So, if I print the map, I'd like to get the result like m[6] = 1 m[2] = 5 m[4] = 6 m[1] = 10 this. How can I sort like this way? Is there any way that I can deal with the key and value with sorted values?

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  • Significance of Bresenhams Line of Sight algorithm

    - by GamDroid
    What is the significance of Bresenhams Line of Sight algorithm in chasing and evading in games? As far as i know and implemented this algorithm calulates the straight line between two given points. However while implementing it in game development i stored the points calculated using this algorithm in an array.Then im traversing this array for chasing and evading purpose. This looks to be working good with some angles only.In an pixel based environment/tile based. What if there are some obstacles added in the paths of the two points? then this algorithm will not work right? How well can we use the Bresenhams Line algorithm in game development?

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  • Bewildering SegFault involving STL sort algorithm.

    - by just_wes
    Hello everybody, I am completely perplexed at a seg fault that I seem to be creating. I have: vector<unsigned int> words; and global variable string input; I define my custom compare function: bool wordncompare(unsigned int f, unsigned int s) { int n = k; while (((f < input.size()) && (s < input.size())) && (input[f] == input[s])) { if ((input[f] == ' ') && (--n == 0)) { return false; } f++; s++; } return true; } When I run the code: sort(words.begin(), words.end()); The program exits smoothly. However, when I run the code: sort(words.begin(), words.end(), wordncompare); I generate a SegFault deep within the STL. The GDB back-trace code looks like this: #0 0x00007ffff7b79893 in std::string::size() const () from /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/libstdc++.so.6 #1 0x0000000000400f3f in wordncompare (f=90, s=0) at text_gen2.cpp:40 #2 0x000000000040188d in std::__unguarded_linear_insert<__gnu_cxx::__normal_iterator<unsigned int*, std::vector<unsigned int, std::allocator<unsigned int> > >, unsigned int, bool (*)(unsigned int, unsigned int)> (__last=..., __val=90, __comp=0x400edc <wordncompare(unsigned int, unsigned int)>) at /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_algo.h:1735 #3 0x00000000004018df in std::__unguarded_insertion_sort<__gnu_cxx::__normal_iterator<unsigned int*, std::vector<unsigned int, std::allocator<unsigned int> > >, bool (*)(unsigned int, unsigned int)> (__first=..., __last=..., __comp=0x400edc <wordncompare(unsigned int, unsigned int)>) at /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_algo.h:1812 #4 0x0000000000402562 in std::__final_insertion_sort<__gnu_cxx::__normal_iterator<unsigned int*, std::vector<unsigned int, std::allocator<unsigned int> > >, bool (*)(unsigned int, unsigned int)> (__first=..., __last=..., __comp=0x400edc <wordncompare(unsigned int, unsigned int)>) at /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_algo.h:1845 #5 0x0000000000402c20 in std::sort<__gnu_cxx::__normal_iterator<unsigned int*, std::vector<unsigned int, std::allocator<unsigned int> > >, bool (*)(unsigned int, unsigned int)> (__first=..., __last=..., __comp=0x400edc <wordncompare(unsigned int, unsigned int)>) at /usr/lib/gcc/x86_64-pc-linux-gnu/4.3.4/include/g++-v4/bits/stl_algo.h:4822 #6 0x00000000004012d2 in main (argc=1, args=0x7fffffffe0b8) at text_gen2.cpp:70 I have similar code in another program, but in that program I am using a vector instead of vector. For the life of me I can't figure out what I'm doing wrong. Thanks!

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  • STL vector reserve() and copy()

    - by natersoz
    Greetings, I am trying to perform a copy from one vector (vec1) to another vector (vec2) using the following 2 abbreviated lines of code (full test app follows): vec2.reserve( vec1.size() ); copy(vec1.begin(), vec1.end(), vec2.begin()); While the call to vec2 sets the capacity of vector vec2, the copying of data to vec2 seems to not fill in the values from vec1 to vec2. Replacing the copy() function with calls to push_back() works as expected. What am I missing here? Thanks for your help. vectest.cpp test program followed by resulting output follows. Compiler: gcc 3.4.4 on cygwin. Nat /** * vectest.cpp */ #include <iostream> #include <vector> using namespace std; int main() { vector<int> vec1; vector<int> vec2; vec1.push_back(1); vec1.push_back(2); vec1.push_back(3); vec1.push_back(4); vec1.push_back(5); vec1.push_back(6); vec1.push_back(7); vec2.reserve( vec1.size() ); copy(vec1.begin(), vec1.end(), vec2.begin()); cout << "vec1.size() = " << vec1.size() << endl; cout << "vec1.capacity() = " << vec1.capacity() << endl; cout << "vec1: "; for( vector<int>::const_iterator iter = vec1.begin(); iter < vec1.end(); ++iter ) { cout << *iter << " "; } cout << endl; cout << "vec2.size() = " << vec2.size() << endl; cout << "vec2.capacity() = " << vec2.capacity() << endl; cout << "vec2: "; for( vector<int>::const_iterator iter = vec2.begin(); iter < vec2.end(); ++iter ) { cout << *iter << endl; } cout << endl; } output: vec1.size() = 7 vec1.capacity() = 8 vec1: 1 2 3 4 5 6 7 vec2.size() = 0 vec2.capacity() = 7 vec2:

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  • [c++/STL] Selective iterator

    - by rubenvb
    FYI: no boost, yes it has this, I want to reinvent the wheel ;) Is there some form of a selective iterator (possible) in C++? What I want is to seperate strings like this: some:word{or other to a form like this: some : word { or other I can do that with two loops and find_first_of(":") and ("{") but this seems (very) inefficient to me. I thought that maybe there would be a way to create/define/write an iterator that would iterate over all these values with for_each. I fear this will have me writing a full-fledged custom way-too-complex iterator class for a std::string. So I thought maybe this would do: std::vector<size_t> list; size_t index = mystring.find(":"); while( index != std::string::npos ) { list.push_back(index); index = mystring.find(":", list.back()); } std::for_each(list.begin(), list.end(), addSpaces(mystring)); This looks messy to me, and I'm quite sure a more elegant way of doing this exists. But I can't think of it. Anyone have a bright idea? Thanks PS: I did not test the code posted, just a quick write-up of what I would try

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  • The best algorithm enhancing alpha-beta?

    - by Risa
    I'm studying AI. My teacher gave us source code of a chess-like game and asked us to enhance it. My exercise is to improve the alpha/beta algorithm implementing in that game. The programmer already uses transposition tables, MTD(f) with alpha/beta+memory (MTD(f) is the best algorithm I know by far). So is there any better algorithm to enhance alpha-beta search or a good way to implement MTD(f) in coding a game?

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  • Matchmaking algorithm with a set of filters

    - by Yuriy Pogrebnyak
    I'm looking for matchmaking algorithm for 1x1 online game. Players must be matched not by their skill or level, as usual, but by some specific filters. Each player sends request, where he specifies some set of parameters (generally, 2-4 parameters). If some parameter is specified, player can be matched only with those who has sent this parameter with exactly the same value, or those who hasn't specified this parameter. I need this algorithm to be thread-safe and preferably fast. It would be great if it'll work for 3-4 or even more parameters, but also I'm looking for algorithm that works with only one parameter (in my case it's game bet). Also I'd appreciate ideas on how to implement or improve this algorithm on my server platform - ASP.NET. One more problem I'm facing is that finding match can't be executed right after user sends request, because if other user sends request before matching for previous is finished, they won't be matched even is they possibly could. So it seems that match finding should be started on schedule, and I need help on how to optimize it and how to choose time interval for starting new match finding. P.S. I've also posted this question on stackoverflow

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  • The C++ Standard Template Library as a BDB Database (part 1)

    - by Gregory Burd
    If you've used C++ you undoubtedly have used the Standard Template Libraries. Designed for in-memory management of data and collections of data this is a core aspect of all C++ programs. Berkeley DB is a database library with a variety of APIs designed to ease development, one of those APIs extends and makes use of the STL for persistent, transactional data storage. dbstl is an STL standard compatible API for Berkeley DB. You can make use of Berkeley DB via this API as if you are using C++ STL classes, and still make full use of Berkeley DB features. Being an STL library backed by a database, there are some important and useful features that dbstl can provide, while the C++ STL library can't. The following are a few typical use cases to use the dbstl extensions to the C++ STL for data storage. When data exceeds available physical memory.Berkeley DB dbstl can vastly improve performance when managing a dataset which is larger than available memory. Performance suffers when the data can't reside in memory because the OS is forced to use virtual memory and swap pages of memory to disk. Switching to BDB's dbstl improves performance while allowing you to keep using STL containers. When you need concurrent access to C++ STL containers.Few existing C++ STL implementations support concurrent access (create/read/update/delete) within a container, at best you'll find support for accessing different containers of the same type concurrently. With the Berkeley DB dbstl implementation you can concurrently access your data from multiple threads or processes with confidence in the outcome. When your objects are your database.You want to have object persistence in your application, and store objects in a database, and use the objects across different runs of your application without having to translate them to/from SQL. The dbstl is capable of storing complicated objects, even those not located on a continous chunk of memory space, directly to disk without any unnecessary overhead. These are a few reasons why you should consider using Berkeley DB's C++ STL support for your embedded database application. In the next few blog posts I'll show you a few examples of this approach, it's easy to use and easy to learn.

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  • Control diamond square algorithm to generate islands/pangea.

    - by Gabriel A. Zorrilla
    I generated a height map with the diamond square algorithm. The thing is i do not manage to create islands, this is, restrict the height other than water level range to a certain value in the center of the map. I manualy seeded a circle in the middle of the map but the rest of the map still receives heights over the water level. I dont fully understand the Perlin noise algorithm so i'd like to work with my current implementation of the diamond square algorithm which took me 3 days to interpret and code in PHP. :P

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  • word disambiguation algorithm (Lesk algorithm)

    - by anyssnordin
    Hii.. Can anybody help me to find an algorithm in Java code to find synonyms of a search word based on the context and I want to implement the algorithm with WordNet database. For example, "I am running a Java program". From the context, I want to find the synonyms for the word "running", but the synonyms must be suitable according to a context.

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  • is c++ STL algorithms and containers same across platforms and performance?

    - by Abhilash M
    After learning good amount of c++, i'm now into STL containers and algorithms template library, my major concerns are, 1) Is this library same across different platforms like MS, linux n other os? 2) will quality or efficiency of program c++ module decrease with more use of STL containers and algorithms, i think i can't customize it to all needs. 3) Is this template library good to use in linux system programming, kernel modules? 4) lastly can i use this in programming contests, because it relives a lot of coding and pressure off shoulders.

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  • Hopcroft–Karp algorithm in Python

    - by Simon
    I am trying to implement the Hopcroft Karp algorithm in Python using networkx as graph representation. Currently I am as far as this: #Algorithms for bipartite graphs import networkx as nx import collections class HopcroftKarp(object): INFINITY = -1 def __init__(self, G): self.G = G def match(self): self.N1, self.N2 = self.partition() self.pair = {} self.dist = {} self.q = collections.deque() #init for v in self.G: self.pair[v] = None self.dist[v] = HopcroftKarp.INFINITY matching = 0 while self.bfs(): for v in self.N1: if self.pair[v] and self.dfs(v): matching = matching + 1 return matching def dfs(self, v): if v != None: for u in self.G.neighbors_iter(v): if self.dist[ self.pair[u] ] == self.dist[v] + 1 and self.dfs(self.pair[u]): self.pair[u] = v self.pair[v] = u return True self.dist[v] = HopcroftKarp.INFINITY return False return True def bfs(self): for v in self.N1: if self.pair[v] == None: self.dist[v] = 0 self.q.append(v) else: self.dist[v] = HopcroftKarp.INFINITY self.dist[None] = HopcroftKarp.INFINITY while len(self.q) > 0: v = self.q.pop() if v != None: for u in self.G.neighbors_iter(v): if self.dist[ self.pair[u] ] == HopcroftKarp.INFINITY: self.dist[ self.pair[u] ] = self.dist[v] + 1 self.q.append(self.pair[u]) return self.dist[None] != HopcroftKarp.INFINITY def partition(self): return nx.bipartite_sets(self.G) The algorithm is taken from http://en.wikipedia.org/wiki/Hopcroft%E2%80%93Karp_algorithm However it does not work. I use the following test code G = nx.Graph([ (1,"a"), (1,"c"), (2,"a"), (2,"b"), (3,"a"), (3,"c"), (4,"d"), (4,"e"),(4,"f"),(4,"g"), (5,"b"), (5,"c"), (6,"c"), (6,"d") ]) matching = HopcroftKarp(G).match() print matching Unfortunately this does not work, I end up in an endless loop :(. Can someone spot the error, I am out of ideas and I must admit that I have not yet fully understand the algorithm, so it is mostly an implementation of the pseudo code on wikipedia

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  • Space partitioning algorithm

    - by Karol Kolenda
    I have a set of points which are contained within the rectangle. I'd like to split the rectangles into subrectangles based on point density (giving a number of subrectangles or desired density, whichever is easiest). The partitioning doesn't have to be exact (almost any approximation better than regular grid would do), but the algorithm have to cope with the large number of points - approx. 200 millions. The desired number of subrectangles however is substantially lower (around 1000). Does anyone knows any algorithm which may help me with this particular task?

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  • Polygonal Triangulation - algorithm with O(n log n) complexity

    - by Arthur Wulf White
    I wish to triangulate a polygon I only have the outline of (p0, p1, p2 ... pn) like described in this question: polygon triangulation algorithm and this webpage: http://cgm.cs.mcgill.ca/~godfried/teaching/cg-projects/97/Ian/algorithm2.html I do not wish to learn the subject and have a deep understanding of it at the moment. I only want to see an effective algorithm that can be used out of the box. The one described in the site seems to be of somewhat high complexity O(n) for finding one ear. I heard this could be done in O(n log n) time. Is there any well known easy to use algorithm that I can translate port to use in my engine that runs with somewhat reasonable complexity? The reason I need to triangulate is that I wish to feel out a 2d-outline and render it 3d. Much like we fill out a 2d-outline in paint. I could use sprites. This would not serve cause I am planning to play with the resulting model on the z-axis, giving it different heights in the different areas. I would love to try the books that were mentioned, although I suspect that is not the answer most readers are hoping for when they read this Q & A format. Mostly I like to see a code snippet I can cut and paste with some modifications and start running.

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  • Non-perfect maze generation algorithm

    - by Shylux
    I want to generate a maze with the following properties: The maze is non-perfect. Means it has loops and multiple ways to reach the exit. The maze should be random. The algorithm should output different mazes for different input parameters The maze doesn't have to be braided. Means dead-ends are allowed and appreciated. I just can't find the right resources on google. The closest i found was this description of the different types of algorithms: http://www.astrolog.org/labyrnth/algrithm.htm. All other algorithms were for perfect mazes. Can anyone give me a website where i can look this up or maybe an algorithm directly?

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  • Quick 2D sight area calculation algorithm?

    - by Rogach
    I have a matrix of tiles, on some of that tiles there are objects. I want to calculate which tiles are visible to player, and which are not, and I need to do it quite efficiently (so it would compute fast enough even when I have a big matrices (100x100) and lots of objects). I tried to do it with Besenham's algorithm, but it was slow. Also, it gave me some errors: ----XXX- ----X**- ----XXX- -@------ -@------ -@------ ----XXX- ----X**- ----XXX- (raw version) (Besenham) (correct, since tunnel walls are still visible at distance) (@ is the player, X is obstacle, * is invisible, - is visible) I'm sure this can be done - after all, we have NetHack, Zangband, and they all dealt with this problem somehow :) What algorithm can you recommend for this? EDIT: Definition of visible (in my opinion): tile is visible when at least a part (e.g. corner) of the tile can be connected to center of player tile with a straight line which does not intersect any of obstacles.

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  • Dijkstra's Bankers Algorithm

    - by idea_
    Could somebody please provide a step-through approach to solving the following problem using the Banker's Algorithm? How do I determine whether a "safe-state" exists? What is meant when a process can "run to completion"? In this example, I have four processes and 10 instances of the same resource. Resources Allocated | Resources Needed Process A 1 6 Process B 1 5 Process C 2 4 Process D 4 7

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