stl-algorithm

I have sets of pairs of int like set<pair<int,int> > x1, x2, ... xn ( n can be between 2 and 20). What is the fastest way to find union of those sets ? Sorry If I wasn't make clear at the beginning, I meant fast in performance, memory allocation is not a problem. Unfortunately, I believe that you are limited to a linear O(N) solution, as all a union would be is a combination of the elements in both sets. template<typename S> S union_sets(const S& s1, const S& s2) { S result = s1; result.insert(s2.cbegin(), s2.cend()); return result; } Assuming that the result needs to be a set too, then you

When thinking about this question I start to wondering if std::copy() and/or std::fill are specialized (I really mean optimized) for std::vector<bool> . Is this required by C++ standard or, perhaps, it is common approach by C++ std library vendors? Simple speaking, I wonder to know if the following code: std::vector<bool> v(10, false); std::fill(v.begin(), v.end(), true); is in any way better/different than that: std::vector<bool> v(10, false); for (auto it = v.begin(); it != v.end(); ++it) *it = true; To be very strict - can, let say: std::fill<std::vector<bool>::iterator>() go into internal

This question with an added constraint. I'm willing to allow not-uniform selection as long as it's not to lop sided. Given that " sets are typically implemented as binary search trees " and I expect they will contain some kind of depth or size information for balancing, I would expect you could do some sort of weighted random walk of the tree. However I don't know of any remotely portable way to do that. Edit: The constraint is NOT for the amortized time. Introduce array with size equal to set. Make array elements hold addresses of every element in set. Generate random integer R bounded by

From the standard, std::includes : Returns: true if [first2, last2) is empty or if every element in the range [first2, last2) is contained in the range [first1, last1) . Returns false otherwise. Note: as this is under [alg.set.operations] , the ranges must be sorted Taking this literally, if we let R1=[first1, last1) and R2=[first2, last2) , this is evaluating: ∀a∈R2 a∈R1 However, this is not what is actually being evaluated. For R1={1} and R2={1,1,1} , std::includes(R1, R2) returns false: #include <algorithm> #include <iomanip> #include <iostream> #include <vector> int main() { std::vector

This question already has an answer here: Nice way to append a vector to itself 4 answers Inspired by this question , asking how to append a vector to itself, my first thought was the following (and yes, I realize insert is a better option now): #include <algorithm> #include <iostream> #include <iterator> #include <vector> int main() { std::vector<int> vec {1, 2, 3}; std::copy (std::begin (vec), std::end (vec), std::back_inserter (vec)); for (const auto &v : vec) std::cout << v << ' '; } However, this prints: 1 2 3 1 * 3 The * is a different number every time the program is run. The fact that