Select random element in an unordered_map

Question

I define an unordered_map like this:

std::unordered_map edges;

Is there a efficient way to choose a rando

Answer 1

The solution of

std::unordered_map edges;
auto random_it = std::next(std::begin(edges), rand_between(0, edges.size()));

is extremely slow....

A much faster solution will be:

• when assigning edges, simutaneously emplaces its keys to std::vector vec
• random an int index ranging from 0 to vec.size() - 1
• then get edges[vec[index]]