Associative container
和原文的组织方式不同，基于是否ordered来进行分类。
cppreference Ordered associative containers
Associative containers implement sorted data structures that can be quickly searched (O(log n) complexity).
| set | collection of unique keys, sorted by keys (class template) |
| map | collection of key-value pairs, sorted by keys, keys are unique (class template) |
| multiset | collection of keys, sorted by keys (class template) |
| multimap | collection of key-value pairs, sorted by keys (class template) |
cppreference Unordered associative containers
Unordered associative containers implement unsorted (hashed) data structures that can be quickly searched (O(1) amortized, O(n) worst-case complexity).
| unordered_set(C++11) | collection of unique keys, hashed by keys (class template) |
| unordered_map(C++11) | collection of key-value pairs, hashed by keys, keys are unique (class template) |
| unordered_multiset(C++11) | collection of keys, hashed by keys (class template) |
| unordered_multimap(C++11) | collection of key-value pairs, hashed by keys (class template) |