How can I optimize an unordered_map in C++11?

How can I optimize an unordered_map in C++11?

To optimize an unordered_map in C++11, consider using a custom hash function and reserving space to minimize reallocations.

What are the benefits of using a custom hash function?

A custom hash function can improve performance by reducing collisions, leading to faster access times.

How do I implement a custom hash function?

You can implement a custom hash function by defining a struct with an overloaded operator() that computes the hash value.

Can you provide an example of a custom hash function?

Sure! Here's a simple example:

struct CustomHash {
    size_t operator()(const std::string& key) const {
        return std::hash<std::string>()(key) ^ (key.size() << 1);
    }
};

This combines the standard hash with a bit manipulation for better distribution.