Glossary: Coding Interviews in C++

Hash map / hash set

Also written: hash map, hash set, unordered_map, unordered_set

Structures that look up, add or count items in O(1) on average, so "have I seen this?" or "how many of each?" needs no nested loop. In C++ they are `std::unordered_map` and `std::unordered_set`.