unordered set in c++ code example

Example 1: what is unordered_set in c++

The structure unordered_set uses hashing, and its operations work in O(1) time
on average.

Example 2: hashset in c++

template < class Key,                        // unordered_set::key_type/value_type
           class Hash = hash<Key>,           // unordered_set::hasher
           class Pred = equal_to<Key>,       // unordered_set::key_equal
           class Alloc = allocator<Key>      // unordered_set::allocator_type
           > class unordered_set;