Miscellanious hash set utility functions.
iterator find(const key_type& x) const;
Returns an iterator to the first element in the container that is equal to x, or if x is not in the container, returns end().
count(const key_type& x) const
Returns the number of elements in the container equal to x.
std::pair<iterator, iterator> equal_range(const key_type& x);
Returns a pair of iterators indicating a range in the container such that all elements in the range are equal to x. If no elements equal to x are in the container, an empty range is returned.