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  • Easier debugging stl array

    - by bobobobo
    In MSVC++ I have a vector. Whenever you go out of bounds of the vector (in debug mode, launched as "Start Debugging"), when you step out of bounds of the vector the program halts with a dialog box: Microsoft Visual C++ Debug Library ==== Debug Assertion Failed! Expression: Vector subscript out of range Abort | Retry | Ignore So what I want though is the MSVC++ debugger within visual studio to STOP AT THE LINE WHERE THE OUT OF BOUNDS OCCURRED, not give me this dialog box. How can I cause the program to "break" properly and be able to step through code /inspect variables when an out of bounds occurs on an STL vector?

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  • STL map inside map C++

    - by Prasanth Madhavan
    In c++ STL map, i have a definition like map<string, map<int, string> >; and i iterate it using the following code. for( map<string, map<int, string> >::iterator ii=info.begin(); ii!=info.end(); ++ii){ for(map<int, string>::iterator j=ii->second.begin(); j!=ii->second.end();++j){ cout << (*ii).first << " : " << (*j).first << " : "<< (*j).second << endl; } } My doubt is is this the correct way to iterate or is there a better way to do so? The above code works for me. But m looking for a more elegant solution.

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  • Hidden Features and Dark Corners of STL?

    - by Andrei
    C++ developers, all know the basics of C++: Declarations, conditionals, loops, operators, etc. Some of us even mastered the stuff like templates, object model, complex I/O, etc. But what are the most hidden features or tricks or dark corners of C++/STL that even C++ fans, addicts, and experts barely know? I am talking about a seasoned C++ programmer (be she/he a developer, student, fan, all three, etc), who thinks (s)he knows something 99% of us never heard or dreamed about. Something that not only makes his/her work easier, but also cool and hackish. After all, C++ is one of the most used programming languages in the world, thus it should have intricacies that only a few privileged know about and want to share with us. Boost is welcome too! One per post with an example please P.S Examples are important for other developers to copy and paste!

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  • Using objects with STL vector - minimal set of methods

    - by osgx
    Hello What is "minimal framework" (necessary methods) of object, which I will use with STL <vector>? For my assumptions: #include <vector> #include <cstring> using namespace std; class Doit { private: char *a; public: Doit(){a=(char*)malloc(10);} ~Doit(){free(a);} }; int main(){ vector<Doit> v(10); } gives *** glibc detected *** ./a.out: double free or corruption (fasttop): 0x0804b008 *** Aborted and in valgrind: malloc/free: 2 allocs, 12 frees, 50 bytes allocated.

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  • Switching from C++ (with a lot of STL use) to C for interpreter building

    - by wndsr
    I'm switching from C++ to C because I'm rebuilding my toy interpreter. I was used to vectors for dynamic allocation of objects like tokens or instructions of my programs, stacks and mainly strings with all their aspects. Now, in C I'm not going to have all these anymore. I know that I will have to use a lot of memory management, too. I'm completely new to C, I only know the high-level easy-life data structures from the STL, how can I get started with strings and dynamic memory allocation?

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  • STL deque accessing by index is O(1)?

    - by jasonline
    I've read that accessing elements by position index can be done in constant time in a STL deque. As far as I know, elements in a deque may be stored in several non-contiguous locations, eliminating safe access through pointer arithmetic. For example: abc-defghi-jkl-mnop The elements of the deque above consists of a single character. The set of characters in one group indicate it is allocated in contiguous memory (e.g. abc is in a single block of memory, defhi is located in another block of memory, etc.). Can anyone explain how accessing by position index can be done in constant time, especially if the element to be accessed is in the second block? Or does a deque have a pointer to the group of blocks? Update: Or is there any other common implementation for a deque?

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  • How to change size of STL container in C++

    - by Jaime Pardos
    I have a piece of performance critical code written with pointers and dynamic memory. I would like to rewrite it with STL containers, but I'm a bit concerned with performance. Is there a way to increase the size of a container without initializing the data? For example, instead of doing ptr = new BYTE[x]; I want to do something like vec.insert(vec.begin(), x, 0); However this initializes every byte to 0. Isn't there a way to just make the vector grow? I know about reserve() but it just allocates memory, it doesn't change the size of the vector, and doesn't allows me to access it until I have inserted valid data. Thank you everyone.

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  • How is the syntax for stl iterators implemented?

    - by Liberalkid
    I've been working on writing a library in my spare time to familiarize myself more with c++ and singular value decomposition. I've been working on writing an Iterator class and I'm entirely capable of writing the functionality and I have already for my own currently MatrixIterator class. I'm guessing that it involves namespaces because: vector<int>::iterator Would appear to be an iterator from the namespace vector, but namespaces are another topic which I'm not familiar with. Mainly I'm asking what would it involve to implement an iterator such that it could be referenced in a similar way to the stl iterators. I'm also aware that I could use boost.iterators or something similar to save myself a lot of work, but I'm more interested in learning all of the details that go into something like this.

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  • C++ STL question related to insert iterators and overloaded operators

    - by rshepherd
    #include <list> #include <set> #include <iterator> #include <algorithm> using namespace std; class MyContainer { public: string value; MyContainer& operator=(const string& s) { this->value = s; return *this; } }; int main() { list<string> strings; strings.push_back("0"); strings.push_back("1"); strings.push_back("2"); set<MyContainer> containers; copy(strings.begin(), strings.end(), inserter(containers, containers.end())); } The preceeding code does not compile. In standard C++ fashion the error output is verbose and difficult to understand. The key part seems to be this... /usr/include/c++/4.4/bits/stl_algobase.h:313: error: no match for ‘operator=’ in ‘__result.std::insert_iterator::operator* [with _Container = std::set, std::allocator ]() = __first.std::_List_iterator::operator* [with _Tp = std::basic_string, std::allocator ]()’ ...which I interpet to mean that the assignment operator needed is not defined. I took a look at the source code for insert_iterator and noted that it has overloaded the assignment operator. The copy algorithm must uses the insert iterators overloaded assignment operator to do its work(?). I guess that because my input iterator is on a container of strings and my output iterator is on a container of MyContainers that the overloaded insert_iterator assignment operator can no longer work. This is my best guess, but I am probably wrong. So, why exactly does this not work and how can I accomplish what I am trying to do?

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  • Storing objects in STL vector - minimal set of methods

    - by osgx
    Hello What is "minimal framework" (necessary methods) of object, which I will store in STL <vector>? For my assumptions: #include <vector> #include <cstring> using namespace std; class Doit { private: char *a; public: Doit(){a=(char*)malloc(10);} ~Doit(){free(a);} }; int main(){ vector<Doit> v(10); } gives *** glibc detected *** ./a.out: double free or corruption (fasttop): 0x0804b008 *** Aborted and in valgrind: malloc/free: 2 allocs, 12 frees, 50 bytes allocated.

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  • Obtain container type from (its) iterator type in C++ (STL)

    - by KRao
    It is easy given a container to get the associated iterators, example: std::vector<double>::iterator i; //An iterator to a std::vector<double> I was wondering if it is possible, given an iterator type, to deduce the type of the "corresponding container" (here I am assuming that for each container there is one and only one (non-const) iterator). More precisely, I would like a template metafunction that works with all STL containers (without having to specialize it manually for each single container) such that, for example: ContainerOf< std::vector<double>::iterator >::type evaluates to std::vector<double> Is it possible? If not, why? Thank you in advance for any help!

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  • STL for games, yea or nay?

    - by munificent
    Every programming language has its standard library of containers, algorithms, and other helpful stuff. With languages like C#, Java, and Python, it's practically inconceivable to use the language without its standard lib. Yet, on many C++ games I've worked on, we either didn't use the STL at all, used a tiny fraction of it, or used our own implementation. It's hard to tell if that was a sound decision for our games, or one simply made out of ignorance of the STL. So... is the STL a good fit or not?

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  • STL for games, yea or nay?

    - by munificent
    Every programming language has its standard library of containers, algorithms, and other helpful stuff. With languages like C#, Java, and Python, it's practically inconceivable to use the language without its standard lib. Yet, on many C++ games I've worked on, we either didn't use the STL at all, used a tiny fraction of it, or used our own implementation. It's hard to tell if that was a sound decision for our games, or one simply made out of ignorance of the STL. So... is the STL a good fit or not?

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  • VS2008 -> VS2010 leads to cryptic STL errors

    - by Jakobud
    The following C++ library was successfully compiled in VS2008 http://sourceforge.net/projects/xmlrpcc4win/files/xmlrpcc4win/XmlRpcC4Win1.0.8.zip/download When I open it in VS2010, it goes through the conversion wizard process without any errors. Now, when I attempt to compile it in VS2010, I get some weird STL errors like these: 1>TimXmlRpc.cpp(1018): error C2039: 'back_insert_iterator' : is not a member of 'std' 1>TimXmlRpc.cpp(1018): error C2065: 'back_insert_iterator' : undeclared identifier 1>TimXmlRpc.cpp(1018): error C2275: 'XmlRpcValue::BinaryData' : illegal use of this type as an expression 1>TimXmlRpc.cpp(1018): error C2065: 'ins' : undeclared identifier 1>TimXmlRpc.cpp(1018): error C2039: 'back_inserter' : is not a member of 'std' 1>TimXmlRpc.cpp(1018): error C3861: 'back_inserter': identifier not found 1>TimXmlRpc.cpp(1019): error C2065: 'ins' : undeclared identifier 1>TimXmlRpc.cpp(1031): error C2039: 'back_insert_iterator' : is not a member of 'std' 1>TimXmlRpc.cpp(1031): error C2065: 'back_insert_iterator' : undeclared identifier 1>TimXmlRpc.cpp(1031): error C2275: 'std::vector<_Ty>' : illegal use of this type as an expression 1> with 1> [ 1> _Ty=char 1> ] 1>TimXmlRpc.cpp(1031): error C2065: 'ins' : undeclared identifier 1>TimXmlRpc.cpp(1031): error C2039: 'back_inserter' : is not a member of 'std' 1>TimXmlRpc.cpp(1031): error C3861: 'back_inserter': identifier not found 1>TimXmlRpc.cpp(1032): error C2065: 'ins' : undeclared identifier I'm not sure what to make of some of these. For instance, back_insert_iterator is in fact a member of std, but VS doesn't seem to think it is. How do I fix errors like these? They just don't seem to make much sense so I'm not sure where to begin. Perhaps its something in my project settings? For example, here is line 1018, which gives the std error: std::back_insert_iterator<BinaryData> ins = std::back_inserter(*(u.asBinary)); If anyone could give me some direction I'd appreciate it. I'm new enough to C++ that I'm having a tough time figuring out this one.

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  • maps, iterators, and complex structs - STL errors

    - by Austin Hyde
    So, I have two structs: struct coordinate { float x; float y; } struct person { int id; coordinate location; } and a function operating on coordinates: float distance(const coordinate& c1, const coordinate& c2); In my main method, I have the following code: map<int,person> people; // populate people map<int,map<float,int> > distance_map; map<int,person>::iterator it1,it2; for (it1=people.begin(); it1!=people.end(); ++it1) { for (it2=people.begin(); it2!=people.end(); ++it2) { float d = distance(it1->second.location,it2->second.location); distance_map[it1->first][d] = it2->first; } } However, I get the following error upon build: stl_iterator_base_types.h: In instantiation of ‘std::iterator_traits<coordinate>’: stl_iterator_base_types.h:129: error: no type named ‘iterator_category’ in ‘struct coordinate’ stl_iterator_base_types.h:130: error: no type named ‘value_type’ in ‘struct coordinate’ stl_iterator_base_types.h:131: error: no type named ‘difference_type’ in ‘struct coordinate’ stl_iterator_base_types.h:132: error: no type named ‘pointer’ in ‘struct coordinate’ stl_iterator_base_types.h:133: error: no type named ‘reference’ in ‘struct coordinate’ And it blames it on the line: float d = distance(it1->second.location,it2->second.location); Why does the STL complain about my code?

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  • shared memory STL maps

    - by user306963
    Hello, I am writing an Apache module in C++. I need to store the common data that all childs need to read as a portion of shared memory. Structure is kind of map of vectors, so I want to use STL map and vectors for it. I have written a shared allocator and a shared manager for the purpose, they work fine for vectors but not for maps, below is the example: typedef vector<CustomersData, SharedAllocator<CustomersData> > CustomerVector; CustomerVector spData; //this one works fine typedef SharedAllocator< pair< const int, CustomerVector > > PairAllocator; typedef map< int, CustomerVector, less<int>, PairAllocator > SharedMap; SharedMap spIndex; //this one doesn't work I get compile time errors when I try to use the second object (spIndex), which are someting like: ../SpatialIndex.h:97: error: '((SpatialIndex*)this)-SpatialIndex::spIndex' does not have class type It looks like the compiler cannot determine a type for SharedMap template type, which is strange in my opinion, it seems to me that all the template parameters have been specified. Can you help? Thanks Benvenuto

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  • Idiomatic STL: Iterating over a list and inserting elements

    - by mkilling
    I'm writing an algorithm that iterates over a list of points, calculates the distance between them and inserts additional points if the distance is too great. However I seem to be lacking the proper familiarity with STL to come up with an elegant solution. I'm hoping that I can learn something, so I'll just show you my code. You might have some hints for me. for (std::list<PathPoint>::iterator it = ++points_.begin(); it != points_.end(); it++) { Vector curPos = it->getPosition(); Vector prevPos = (--it)->getPosition(); Vector vecFromPrev = curPos - prevPos; float distance = vecFromPrev.abs(); it++; if (distance > MAX_DISTANCE_BETWEEN_POINTS) { int pointsToInsert = (int)(distance / MAX_DISTANCE_BETWEEN_POINTS); Vector curPos = prevPos; for (int i = 0; i < pointsToInsert; i++) { curPos += vecFromPrev / pointsToInsert; it = points_.insert(it, PathPoint(curPos, false)); it++; } } }

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  • How to load/save C++ class instance (using STL containers) to disk

    - by supert
    I have a C++ class representing a hierarchically organised data tree which is very large (~Gb, basically as large as I can get away with in memory). It uses an STL list to store information at each node plus iterators to other nodes. Each node has only one parent, but 0-10 children. Abstracted, it looks something like: struct node { public: node_list_iterator parent; // iterator to a single parent node double node_data_array[X]; map<int,node_list_iterator> children; // iterators to child nodes }; class strategy { private: list<node> tree; // hierarchically linked list of nodes struct some_other_data; public: void build(); // build the tree void save(); // save the tree from disk void load(); // load the tree from disk void use(); // use the tree }; I would like to implement the load() and save() to disk, and it should be fairly fast, however the obvious problems are: I don't know the size in advance; The data contains iterators, which are volatile; My ignorance of C++ is prodigious. Could anyone suggest a pure C++ solution please?

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  • C++ STL question related to insert iterators and sets

    - by rshepherd
    #include #include #include #include using namespace std; class MyContainer { public: string value; MyContainer& operator=(const string& s) { this->value = s; return *this; } }; int main() { list<string> strings; strings.push_back("0"); strings.push_back("1"); strings.push_back("2"); set<MyContainer> containers; copy(strings.begin(), strings.end(), inserter(containers, containers.end())); } The preceeding code does not compile. In typical STL style the error output is verbose and difficult to understand. The key part seems to be this... /usr/include/c++/4.4/bits/stl_algobase.h:313: error: no match for ‘operator=’ in ‘__result.std::insert_iterator::operator* [with _Container = std::set, std::allocator ]() = __first.std::_List_iterator::operator* [with _Tp = std::basic_string, std::allocator ]()’ ...which I interpet to mean that the assignment operator needed is not defined. I took a look at the source code for insert_iterator and noted that it has overloaded the assignment operator. The copy algorithm must uses the insert iterators overloaded assignment operator to do its work(?). I guess that because my input iterator is on a container of strings and my output iterator is on a container of MyContainers that the overloaded insert_iterator assignment operator can no longer work. This is my best guess, but I am probably wrong. So, why exactly does this not work and how can I accomplish what I am trying to do?

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  • Fast block placement algorithm, advice needed?

    - by James Morris
    I need to emulate the window placement strategy of the Fluxbox window manager. As a rough guide, visualize randomly sized windows filling up the screen one at a time, where the rough size of each results in an average of 80 windows on screen without any window overlapping another. It is important to note that windows will close and the space that closed windows previously occupied becomes available once more for the placement of new windows. The window placement strategy has three binary options: Windows build horizontal rows or vertical columns (potentially) Windows are placed from left to right or right to left Windows are placed from top to bottom or bottom to top Why is the algorithm a problem? It needs to operate to the deadlines of a real time thread in an audio application. At this moment I am only concerned with getting a fast algorithm, don't concern yourself over the implications of real time threads and all the hurdles in programming that that brings. So far I have two choices which I have built loose prototypes for: 1) A port of the Fluxbox placement algorithm into my code. The problem with this is, the client (my program) gets kicked out of the audio server (JACK) when I try placing the worst case scenario of 256 blocks using the algorithm. This algorithm performs over 14000 full (linear) scans of the list of blocks already placed when placing the 256th window. 2) My alternative approach. Only partially implemented, this approach uses a data structure for each area of rectangular free unused space (the list of windows can be entirely separate, and is not required for testing of this algorithm). The data structure acts as a node in a doubly linked list (with sorted insertion), as well as containing the coordinates of the top-left corner, and the width and height. Furthermore, each block data structure also contains four links which connect to each immediately adjacent (touching) block on each of the four sides. IMPORTANT RULE: Each block may only touch with one block per side. The problem with this approach is, it's very complex. I have implemented the straightforward cases where 1) space is removed from one corner of a block, 2) splitting neighbouring blocks so that the IMPORTANT RULE is adhered to. The less straightforward case, where the space to be removed can only be found within a column or row of boxes, is only partially implemented - if one of the blocks to be removed is an exact fit for width (ie column) or height (ie row) then problems occur. And don't even mention the fact this only checks columns one box wide, and rows one box tall. I've implemented this algorithm in C - the language I am using for this project (I've not used C++ for a few years and am uncomfortable using it after having focused all my attention to C development, it's a hobby). The implementation is 700+ lines of code (including plenty of blank lines, brace lines, comments etc). The implementation only works for the horizontal-rows + left-right + top-bottom placement strategy. So I've either got to add some way of making this +700 lines of code work for the other 7 placement strategy options, or I'm going to have to duplicate those +700 lines of code for the other seven options. Neither of these is attractive, the first, because the existing code is complex enough, the second, because of bloat. The algorithm is not even at a stage where I can use it in the real time worst case scenario, because of missing functionality, so I still don't know if it actually performs better or worse than the first approach. What else is there? I've skimmed over and discounted: Bin Packing algorithms: their emphasis on optimal fit does not match the requirements of this algorithm. Recursive Bisection Placement algorithms: sounds promising, but these are for circuit design. Their emphasis is optimal wire length. Both of these, especially the latter, all elements to be placed/packs are known before the algorithm begins. I need an algorithm which works accumulatively with what it is given to do when it is told to do it. What are your thoughts on this? How would you approach it? What other algorithms should I look at? Or even what concepts should I research seeing as I've not studied computer science/software engineering? Please ask questions in comments if further information is needed. [edit] If it makes any difference, the units for the coordinates will not be pixels. The units are unimportant, but the grid where windows/blocks/whatever can be placed will be 127 x 127 units.

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  • C++ STL make_heap and pop_heap not working.

    - by Henrique
    I need to use a Heap, so i've searched about the STL one, but it doesn't seem to work, i wrote some code to explain what i mean: #include <stdio.h> #include <stdlib.h> #include <vector> #include <algorithm> struct data { int indice; int tamanho; }; bool comparator2(const data* a, const data* b) { return (a->tamanho < b->tamanho); } int main() { std::vector<data*> mesas; data x1, x2, x3, x4, x5; x1.indice = 1; x1.tamanho = 3; x2.indice = 2; x2.tamanho = 5; x3.indice = 3; x3.tamanho = 2; x4.indice = 4; x4.tamanho = 6; x5.indice = 5; x5.tamanho = 4; mesas.push_back(&x1); mesas.push_back(&x2); mesas.push_back(&x3); mesas.push_back(&x4); mesas.push_back(&x5); make_heap(mesas.begin(), mesas.end(), comparator2); for(int i = 0 ; i < 5 ; i++) { data* mesa = mesas.front(); pop_heap(mesas.begin(),mesas.end()); mesas.pop_back(); printf("%d, %d\n", mesa->indice, mesa->tamanho); } return 0; }; and this is what i get: 4, 6 2, 5 1, 3 3, 2 5, 4 So it's not working as a heap, as the maximum element on the vector is not being returned right. Or am i doing something wrong?

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  • Is it a good idea to create an STL iterator which is noncopyable?

    - by BillyONeal
    Most of the time, STL iterators are CopyConstructable, because several STL algorithms require this to improve performance, such as std::sort. However, I've been working on a pet project to wrap the FindXFile API (previously asked about), but the problem is it's impossible to implement a copyable iterator around this API. A find handle cannot be duplicated by any means -- DuplicateHandle specifically forbids passing handles to it. And if you just maintain a reference count to the find handle, then a single increment by any copy results in an increment of all copies -- clearly that is not what a copy constructed iterator is supposed to do. Since I can't satisfy the traditional copy constructible requirement for iterators here, is it even worth trying to create an "STL style" iterator? On one hand, creating some other enumeration method is going to not fall into normal STL conventions, but on the other, following STL conventions are going to confuse users of this iterator if they try to CopyConstruct it later. Which is the lesser of two evils?

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  • What is the right approach when using STL container for median calculation?

    - by sharkin
    Let's say I need to retrieve the median from a sequence of 1000000 random numeric values. If using anything but STL::list, I have no (built-in) way to sort sequence for median calculation. If using STL::list, I can't randomly access values to retrieve middle (median) of sorted sequence. Is it better to implement sorting myself and go with e.g. STL::vector, or is it better to use STL::list and use STL::list::iterator to for-loop-walk to the median value? The latter seems less overheadish, but also feels more ugly.. Or are there more and better alternatives for me?

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  • Algorithm design, "randomising" timetable schedule in Python although open to other languages.

    - by S1syphus
    Before I start I should add I am a musician and not a native programmer, this was undertook to make my life easier. Here is the situation, at work I'm given a new csv file each which contains a list of sound files, their length, and the minimum total amount of time they must be played. I create a playlist of exactly 60 minutes, from this excel file. Each sample played the by the minimum number of instances, but spread out from each other; so there will never be a period where for where one sound is played twice in a row or in close proximity to itself. Secondly, if the minimum instances of each song has been used, and there is still time with in the 60 min, it needs to fill the remaining time using sounds till 60 minutes is reached, while adhering to above. The smallest duration possible is 15 seconds, and then multiples of 15 seconds. Here is what I came up with in python and the problems I'm having with it, and as one user said its buggy due to the random library used in it. So I'm guessing a total rethink is on the table, here is where I need your help. Whats is the best way to solve the issue, I have had a brief look at things like knapsack and bin packing algorithms, while both are relevant neither are appropriate and maybe a bit beyond me.

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