1. std::list.
2. std::forward_list.
3. std::map.
4. std::multimap.
5. std::set.
6. std::unordered_map.
7. std::unordered_multimap.
8. std::unordered_set.
9. Erase-remove idiom on std::vector.
10. Filtering duplicates.
11. Fast or safe way to access std::array or std::vector.
12. Word frequency counter.