C++ unordered_set Features Explained

An unordered_set is a container in the C++ standard library that offers a collection of unique elements without a specific order. Here are some features of unordered_set:

1. Lack of order: The elements in an unordered_set do not have a fixed order; they are stored and accessed based on the result of a hash function. This makes the order of elements in an unordered_set unpredictable.
2. Uniqueness: The elements in an unordered set are unique, any duplicate elements will automatically be ignored. This is ensured by using a hash function and an equality operator.
3. Quickly find: Because unordered_set uses a hash table to store elements, the average time complexity for the find operation is constant.
4. The efficiency of insertion and deletion is high: Because unordered_set uses a hash table to store elements, the time complexity of insertion and deletion operations is also constant.
5. Elements cannot be accessed directly: the elements in an unordered_set are unordered, so they cannot be accessed directly using an index or iterator. Elements can only be accessed through lookup or iterating through the set.
6. High memory usage: Due to unordered_set using a hash table to store elements, it requires extra memory to store the index of the hash table. Therefore, unordered_set has a larger memory footprint compared to other containers.

It is important to note that unordered_set was introduced in C++11, so ensure that the compiler supports the C++11 standard when using it.