unordered-set

Is there an easy way to add all the elements of a vector to an unordered_set ? They are of the same type. Right now, I am using a for loop and was wondering if there is a better way to do it If you're constructing the unordered_set then: std::vector<int> v; std::unordered_set<int> s(v.begin(), v.end()); Forgive me if my syntax has any minor bugs, but you can try the std::copy function , its meant for this purpose. std::vector<int> v; std::unordered_set<int> s; std::copy(v.begin(),v.end(),std::inserter(s,s.end())); 来源： https://stackoverflow.com/questions/12850927/adding-elements-of-a-vector-to

In my application I have the following requirements - The data structure will be populated just once with some values (not key/value pairs). The values may be repeated but I want the data structure to store them once only. I will be iterating 100s of times through all the elements of the data structure created above. The order in which the elements appear in the iteration is immaterial. Constraint 1 suggests that I will either have to use set or unordered_set as data is not in the form of key value pairs. Now set insertion is costlier than unordered_set insertion but the data structure is

How can I store objects of a class in an unordered_set ? My program needs to frequently check if an object exists in this unordered_set and if it does, then do some update on that object. I have looked up online on how to use unordered_set , but sadly most tutorials are about using it on int or string types. But how can I use it on a class? How can I define a hash function to make the node_id in the following example the key of the unordered_set ? #include <iostream> #include <unordered_set> using namespace std; // How can I define a hash function that makes 'node' use 'node_id' as key? struct

I'll start by illustrating a simple use case example: Consider the problem of a social security ID database, where in C++ code is modelled as a std::unordered_map where its key is the social security ID of a person and its value is a std::string with the full-name of that person (e.g., std::unordered_map<int, std::string> DB; ). Consider also, that there's a request for printing this database sorted in ascending order based on the person's ID (i.e., std::unordered_map 's key). Naively, one would think to use std::sort in order to sort the std::unordered_map according to the requested criteria

Here is my code, wondering any ideas to make it faster? My implementation is brute force, which is for any elements in a, try to find if it also in b, if so, put in result set c. Any smarter ideas is appreciated. #include <iostream> #include <unordered_set> int main() { std::unordered_set<int> a = {1,2,3,4,5}; std::unordered_set<int> b = {3,4,5,6,7}; std::unordered_set<int> c; for (auto i = a.begin(); i != a.end(); i++) { if (b.find(*i) != b.end()) c.insert(*i); } for (int v : c) { std::printf("%d \n", v); } } Asymptotically, your algorithm is as good as it can get. In practice, I'd add a

I have a set like this: set<weak_ptr<Node>, owner_less<weak_ptr<Node> > > setName; It works fine. But I would like to change it to an unordered set. However, I get about six pages of errors when I do that. Any ideas how to do that? After looking through all the pages of error messages I found to lines that might help. /usr/include/c++/4.7/bits/functional_hash.h:60:7: error: static assertion failed: std::hash is not specialized for this type /usr/include/c++/4.7/bits/stl_function.h: In instantiation of ‘bool std::equal_to<_Tp>::operator()(const _Tp&, const _Tp&) const [with _Tp = std::weak_ptr