Using an unordered set and map

In the previous recipe, we saw how string comparison can be optimized using hashing. After reading it, the following question may arise: can we make a container that will cache hashed values to use faster comparison?

The answer is yes, and we can do much more. We may achieve almost constant search, insertion, and removal times for elements.

Getting ready

Basic knowledge about C++ and STL containers are required. Reading the previous recipe will also help.

How to do it...

This will be the simplest of all recipes:

1. All you need to do is just include the <boost/unordered_map.hpp> header, if you wish to use maps. If we wish to use sets, include the <boost/unordered_set.hpp> header.
2. Now, you are free to use boost::unordered_map instead of std::map and boost::unordered_set instead of std::set:

#include <boost/unordered_set.hpp>
#include <string>
#include <cassert>

void example() {
    boost::unordered_set<std::string> strings;

    strings...