C++ unordered_set of vectors
c++, c++11, vector
Solution
Sure you can. You'll have to come up with a hash though, since the default one (`std::hash<std::vector<int>>`) will not be implemented. For example, based on this answer, we can build:
struct VectorHash {
size_t operator()(const std::vector<int>& v) const {
std::hash<int> hasher;
size_t seed = 0;
for (int i : v) {
seed ^= hasher(i) + 0x9e3779b9 + (seed<<6) + (seed>>2);
}
return seed;
}
};
And then:
using MySet = std::unordered_set<std::vector<int>, VectorHash>;
You could also, if you so choose, instead add a specialization to `std::hash<T>` for this type (note this could be undefined behavior with `std::vector<int>`, but is definitely okay with a user-defined type):
namespace std {
template <>
struct hash<std::vector<int>> {
size_t operator()(const vector<int>& v) const {
// same thing
}
};
}
using MySet = std::unordered_set<std::vector<int>>;
Problem
Can I create a unordered_set of vectors in C++? something like this ``` std::unordered_set<std::vector<int>> s1; ``` because I know that is possible with the "set" class of the std lib but seems that it doesn't work for the unordered version thanks Update: this is the exactly code that I'm trying to use ``` typedef int CustomerId; typedef std::vector<CustomerId> Route; typedef std::unordered_set<Route> Plan; // ... in the main Route r1 = { 4, 5, 2, 10 }; Route r2 = { 1, 3, 8 , 6 }; Route r3 = { 9, 7 }; Plan p = { r1, r2 }; ``` and it's all right if I use set, but I receive a compilation error when try to use the unordered version ``` main.cpp:46:11: error: non-aggregate type 'Route' (aka 'vector<CustomerId>') cannot be initialized with an initializer list Route r3 = { 9, 7 }; ```