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## Class template multiset

boost::container::multiset

## Synopsis

    // In header: <boost/container/set.hpp>

    template<typename Key, typename Compare = std::less<Key>,
             typename Allocator = new_allocator<Key>,
             typename Options = tree_assoc_defaults>
    class multiset {
    public:
      // types
      typedef Key                                                                     key_type;
      typedef Key                                                                     value_type;
      typedef Compare                                                                 key_compare;
      typedef key_compare                                                             value_compare;
      typedef base_t::allocator_type                                                  allocator_type;
      typedef ::boost::container::allocator_traits< allocator_type >                  allocator_traits_type;
      typedef ::boost::container::allocator_traits< allocator_type >::pointer         pointer;
      typedef ::boost::container::allocator_traits< allocator_type >::const_pointer   const_pointer;
      typedef ::boost::container::allocator_traits< allocator_type >::reference       reference;
      typedef ::boost::container::allocator_traits< allocator_type >::const_reference const_reference;
      typedef ::boost::container::allocator_traits< allocator_type >::size_type       size_type;
      typedef ::boost::container::allocator_traits< allocator_type >::difference_type difference_type;
      typedef implementation_defined                                                  stored_allocator_type;
      typedef implementation_defined                                                  iterator;
      typedef implementation_defined                                                  const_iterator;
      typedef implementation_defined                                                  reverse_iterator;
      typedef implementation_defined                                                  const_reverse_iterator;
      typedef implementation_defined                                                  node_type;

      // construct/copy/destruct
      multiset() noexcept(dtl::is_nothrow_default_constructible< allocator_type >::value &&dtl::is_nothrow_default_constructible< Compare >::value));
      explicit multiset(const allocator_type &);
      explicit multiset(const Compare &);
      multiset(const Compare &, const allocator_type &);
      template<typename InputIterator> multiset(InputIterator, InputIterator);
      template<typename InputIterator>
        multiset(InputIterator, InputIterator, const allocator_type &);
      template<typename InputIterator>
        multiset(InputIterator, InputIterator, const Compare &);
      template<typename InputIterator>
        multiset(InputIterator, InputIterator, const Compare &,
                 const allocator_type &);
      template<typename InputIterator>
        multiset(ordered_range_t, InputIterator, InputIterator);
      template<typename InputIterator>
        multiset(ordered_range_t, InputIterator, InputIterator, const Compare &);
      template<typename InputIterator>
        multiset(ordered_range_t, InputIterator, InputIterator, const Compare &,
                 const allocator_type &);
      template<typename InputIterator>
        multiset(ordered_range_t, InputIterator, InputIterator,
                 const allocator_type &);
      multiset(std::initializer_list< value_type >);
      multiset(std::initializer_list< value_type >, const allocator_type &);
      multiset(std::initializer_list< value_type >, const Compare &);
      multiset(std::initializer_list< value_type >, const Compare &,
               const allocator_type &);
      multiset(ordered_range_t, std::initializer_list< value_type >);
      multiset(ordered_range_t, std::initializer_list< value_type >,
               const Compare &);
      multiset(ordered_range_t, std::initializer_list< value_type >,
               const Compare &, const allocator_type &);
      multiset(const multiset &);
      multiset(multiset &&) noexcept(boost::container::dtl::is_nothrow_move_constructible< Compare >::value));
      multiset(const multiset &, const allocator_type &);
      multiset(multiset &&, const allocator_type &);
      multiset & operator=(const multiset &);
      multiset & operator=(multiset &&) noexcept((allocator_traits_type::propagate_on_container_move_assignment::value||allocator_traits_type::is_always_equal::value) &&boost::container::dtl::is_nothrow_move_assignable< Compare >::value));
      multiset & operator=(std::initializer_list< value_type >);

      // public member functions
      allocator_type get_allocator() const;
      stored_allocator_type & get_stored_allocator();
      const stored_allocator_type & get_stored_allocator() const;
      iterator begin();
      const_iterator begin() const;
      const_iterator cbegin() const;
      iterator end() noexcept;
      const_iterator end() const noexcept;
      const_iterator cend() const noexcept;
      reverse_iterator rbegin() noexcept;
      const_reverse_iterator rbegin() const noexcept;
      const_reverse_iterator crbegin() const noexcept;
      reverse_iterator rend() noexcept;
      const_reverse_iterator rend() const noexcept;
      const_reverse_iterator crend() const noexcept;
      bool empty() const;
      size_type size() const;
      size_type max_size() const;
      template<class... Args> iterator emplace(Args &&...);
      template<class... Args> iterator emplace_hint(const_iterator, Args &&...);
      iterator insert(const value_type &);
      iterator insert(value_type &&);
      iterator insert(const_iterator, const value_type &);
      iterator insert(const_iterator, value_type &&);
      template<typename InputIterator> void insert(InputIterator, InputIterator);
      void insert(std::initializer_list< value_type >);
      iterator insert(node_type &&);
      iterator insert(const_iterator, node_type &&);
      template<typename C2> void merge(multiset< Key, C2, Allocator, Options > &);
      template<typename C2> void merge(multiset< Key, C2, Allocator, Options > &&);
      template<typename C2> void merge(set< Key, C2, Allocator, Options > &);
      template<typename C2> void merge(set< Key, C2, Allocator, Options > &&);
      iterator erase(const_iterator);
      size_type erase(const key_type &);
      iterator erase(const_iterator, const_iterator);
      node_type extract(const_iterator);
      node_type extract(const key_type &);
      void swap(multiset &) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::dtl::is_nothrow_swappable< Compare >::value));
      void clear() noexcept;
      key_compare key_comp() const;
      value_compare value_comp() const;
      iterator find(const key_type &);
      const_iterator find(const key_type &) const;
      template<typename K> iterator find(const K &);
      template<typename K> const_iterator find(const K &) const;
      size_type count(const key_type &) const;
      template<typename K> size_type count(const K &) const;
      bool contains(const key_type &) const;
      template<typename K> bool contains(const K &) const;
      iterator lower_bound(const key_type &);
      const_iterator lower_bound(const key_type &) const;
      template<typename K> iterator lower_bound(const K &);
      template<typename K> const_iterator lower_bound(const K &) const;
      iterator upper_bound(const key_type &);
      const_iterator upper_bound(const key_type &) const;
      template<typename K> iterator upper_bound(const K &);
      template<typename K> const_iterator upper_bound(const K &) const;
      std::pair< const_iterator, const_iterator >
      equal_range(const key_type &) const;
      std::pair< iterator, iterator > equal_range(const key_type &);
      template<typename K>
        std::pair< const_iterator, const_iterator > equal_range(const K &) const;
      template<typename K> std::pair< iterator, iterator > equal_range(const K &);
      void rebalance();

      // friend functions
      friend bool operator==(const multiset &, const multiset &);
      friend bool operator!=(const multiset &, const multiset &);
      friend bool operator<(const multiset &, const multiset &);
      friend bool operator>(const multiset &, const multiset &);
      friend bool operator<=(const multiset &, const multiset &);
      friend bool operator>=(const multiset &, const multiset &);
      friend void swap(multiset &, multiset &);
    };

## Description

A multiset is a kind of associative container that supports equivalent keys (possibly contains multiple copies of the same key value) and provides for fast retrieval of the keys themselves. Class multiset supports bidirectional iterators.

A multiset satisfies all of the requirements of a container and of a reversible container, and of an associative container). multiset also provides most operations described for duplicate keys.

### Template Parameters

1.     typename Key

   is the type to be inserted in the set, which is also the key_type

2.     typename Compare = std::less<Key>

   is the comparison functor used to order keys

3.     typename Allocator = new_allocator<Key>

   is the allocator to be used to allocate memory for this container

4.     typename Options = tree_assoc_defaults

   is an packed option type generated using using `boost::container::tree_assoc_options`.

### `multiset` public construct/copy/destruct

1.     multiset() noexcept(dtl::is_nothrow_default_constructible< allocator_type >::value &&dtl::is_nothrow_default_constructible< Compare >::value));

   Effects: Default constructs an empty set.

   Complexity: Constant.

2.     explicit multiset(const allocator_type & a);

   Effects: Constructs an empty set using the specified allocator object.

   Complexity: Constant.

3.     explicit multiset(const Compare & comp);

   Effects: Constructs an empty set using the specified comparison object.

   Complexity: Constant.

4.     multiset(const Compare & comp, const allocator_type & a);

   Effects: Constructs an empty set using the specified comparison object and allocator.

   Complexity: Constant.

5.     template<typename InputIterator>
         multiset(InputIterator first, InputIterator last);

   Effects: Constructs an empty set using and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

6.     template<typename InputIterator>
         multiset(InputIterator first, InputIterator last, const allocator_type & a);

   Effects: Constructs an empty set using the specified allocator, and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

7.     template<typename InputIterator>
         multiset(InputIterator first, InputIterator last, const Compare & comp);

   Effects: Constructs an empty set using the specified comparison object and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

8.     template<typename InputIterator>
         multiset(InputIterator first, InputIterator last, const Compare & comp,
                  const allocator_type & a);

   Effects: Constructs an empty set using the specified comparison object and allocator, and inserts elements from the range [first ,last ).

   Complexity: Linear in N if the range [first ,last ) is already sorted using the predicate and otherwise N logN, where N is last - first.

9.     template<typename InputIterator>
         multiset(ordered_range_t, InputIterator first, InputIterator last);

   Effects: Constructs an empty multiset and and inserts elements from the ordered range [first ,last ). This function is more efficient than the normal range creation for ordered ranges.

   Requires: [first ,last) must be ordered according to the predicate.

   Complexity: Linear in N.

   Note: Non-standard extension.

10.     template<typename InputIterator>
          multiset(ordered_range_t, InputIterator first, InputIterator last,
                   const Compare & comp);

    Effects: Constructs an empty multiset using the specified comparison object and inserts elements from the ordered range [first ,last ). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [first ,last) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

11.     template<typename InputIterator>
          multiset(ordered_range_t, InputIterator first, InputIterator last,
                   const Compare & comp, const allocator_type & a);

    Effects: Constructs an empty multiset using the specified comparison object and allocator, and inserts elements from the ordered range [first ,last ). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [first ,last) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

12.     template<typename InputIterator>
          multiset(ordered_range_t, InputIterator first, InputIterator last,
                   const allocator_type & a);

    Effects: Constructs an empty multiset using the specified allocator and inserts elements from the ordered range [first ,last ). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [first ,last) must be ordered according to the predicate.

    Complexity: Linear in N.

    Note: Non-standard extension.

13.     multiset(std::initializer_list< value_type > il);

    Effects: Constructs an empty set and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [il.begin(), il.end()) is already sorted using the predicate and otherwise N logN, where N is il.begin() - il.end().

14.     multiset(std::initializer_list< value_type > il, const allocator_type & a);

    Effects: Constructs an empty set using the specified allocator, and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [il.begin(), il.end()) is already sorted using the predicate and otherwise N logN, where N is il.begin() - il.end().

15.     multiset(std::initializer_list< value_type > il, const Compare & comp);

    Effects: Constructs an empty set using the specified comparison object and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [il.begin(), il.end()) is already sorted using the predicate and otherwise N logN, where N is il.begin() - il.end().

16.     multiset(std::initializer_list< value_type > il, const Compare & comp,
                 const allocator_type & a);

    Effects: Constructs an empty set using the specified comparison object and allocator, and inserts elements from the range [il.begin(), il.end()).

    Complexity: Linear in N if the range [il.begin(), il.end()) is already sorted using the predicate and otherwise N logN, where N is il.begin() - il.end().

17.     multiset(ordered_range_t, std::initializer_list< value_type > il);

    Effects: Constructs an empty set and inserts elements from the ordered unique range [il.begin(), il.end()). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [il.begin(), il.end()) must be ordered according to the predicate and must be unique values.

    Complexity: Linear in N.

    Note: Non-standard extension.

18.     multiset(ordered_range_t, std::initializer_list< value_type > il,
                 const Compare & comp);

    Effects: Constructs an empty set using the specified comparison object and inserts elements from the ordered unique range [il.begin(), il.end()). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [il.begin(), il.end()) must be ordered according to the predicate and must be unique values.

    Complexity: Linear in N.

    Note: Non-standard extension.

19.     multiset(ordered_range_t, std::initializer_list< value_type > il,
                 const Compare & comp, const allocator_type & a);

    Effects: Constructs an empty set using the specified comparison object and allocator, and inserts elements from the ordered unique range [il.begin(), il.end()). This function is more efficient than the normal range creation for ordered ranges.

    Requires: [il.begin(), il.end()) must be ordered according to the predicate and must be unique values.

    Complexity: Linear in N.

    Note: Non-standard extension.

20.     multiset(const multiset & x);

    Effects: Copy constructs a set.

    Complexity: Linear in x.size().

21.     multiset(multiset && x) noexcept(boost::container::dtl::is_nothrow_move_constructible< Compare >::value));

    Effects: Move constructs a set. Constructs *this using x's resources.

    Complexity: Constant.

    Postcondition: x is emptied.

22.     multiset(const multiset & x, const allocator_type & a);

    Effects: Copy constructs a set using the specified allocator.

    Complexity: Linear in x.size().

23.     multiset(multiset && x, const allocator_type & a);

    Effects: Move constructs a set using the specified allocator. Constructs *this using x's resources.

    Complexity: Constant if a == x.get_allocator(), linear otherwise.

24.     multiset & operator=(const multiset & x);

    Effects: Makes *this a copy of x.

    Complexity: Linear in x.size().

25.     multiset & operator=(multiset && x) noexcept((allocator_traits_type::propagate_on_container_move_assignment::value||allocator_traits_type::is_always_equal::value) &&boost::container::dtl::is_nothrow_move_assignable< Compare >::value));

    Effects: this->swap(x.get()).

    Throws: If allocator_traits_type::propagate_on_container_move_assignment is false and (allocation throws or value_type's move constructor throws)

    Complexity: Constant if allocator_traits_type:: propagate_on_container_move_assignment is true or this->get>allocator() == x.get_allocator(). Linear otherwise.

26.     multiset & operator=(std::initializer_list< value_type > il);

    Effects: Copy all elements from il to *this.

    Complexity: Linear in il.size().

### `multiset` public member functions

1.     allocator_type get_allocator() const;

   Effects: Returns a copy of the allocator that was passed to the object's constructor.

   Complexity: Constant.

2.     stored_allocator_type & get_stored_allocator();

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

3.     const stored_allocator_type & get_stored_allocator() const;

   Effects: Returns a reference to the internal allocator.

   Throws: Nothing

   Complexity: Constant.

   Note: Non-standard extension.

4.     iterator begin();

   Effects: Returns an iterator to the first element contained in the container.

   Throws: Nothing.

   Complexity: Constant

5.     const_iterator begin() const;

   Effects: Returns a const_iterator to the first element contained in the container.

   Throws: Nothing.

   Complexity: Constant.

6.     const_iterator cbegin() const;

   Effects: Returns a const_iterator to the first element contained in the container.

   Throws: Nothing.

   Complexity: Constant.

7.     iterator end() noexcept;

   Effects: Returns an iterator to the end of the container.

   Throws: Nothing.

   Complexity: Constant.

8.     const_iterator end() const noexcept;

   Effects: Returns a const_iterator to the end of the container.

   Throws: Nothing.

   Complexity: Constant.

9.     const_iterator cend() const noexcept;

   Effects: Returns a const_iterator to the end of the container.

   Throws: Nothing.

   Complexity: Constant.

10.     reverse_iterator rbegin() noexcept;

    Effects: Returns a reverse_iterator pointing to the beginning of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

11.     const_reverse_iterator rbegin() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the beginning of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

12.     const_reverse_iterator crbegin() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the beginning of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

13.     reverse_iterator rend() noexcept;

    Effects: Returns a reverse_iterator pointing to the end of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

14.     const_reverse_iterator rend() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the end of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

15.     const_reverse_iterator crend() const noexcept;

    Effects: Returns a const_reverse_iterator pointing to the end of the reversed container.

    Throws: Nothing.

    Complexity: Constant.

16.     bool empty() const;

    Effects: Returns true if the container contains no elements.

    Throws: Nothing.

    Complexity: Constant.

17.     size_type size() const;

    Effects: Returns the number of the elements contained in the container.

    Throws: Nothing.

    Complexity: Constant.

18.     size_type max_size() const;

    Effects: Returns the largest possible size of the container.

    Throws: Nothing.

    Complexity: Constant.

19.     template<class... Args> iterator emplace(Args &&... args);

    Effects: Inserts an object of type Key constructed with std::forward<Args>(args)... and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic.

20.     template<class... Args>
          iterator emplace_hint(const_iterator p, Args &&... args);

    Effects: Inserts an object of type Key constructed with std::forward<Args>(args)...

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

21.     iterator insert(const value_type & x);

    Effects: Inserts x and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic.

22.     iterator insert(value_type && x);

    Effects: Inserts a copy of x in the container.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

23.     iterator insert(const_iterator p, const value_type & x);

    Effects: Inserts a copy of x in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

24.     iterator insert(const_iterator p, value_type && x);

    Effects: Inserts a value move constructed from x in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

25.     template<typename InputIterator>
          void insert(InputIterator first, InputIterator last);

    Requires: first, last are not iterators into *this.

    Effects: inserts each element from the range [first,last) .

    Complexity: At most N log(size()+N) (N is the distance from first to last)

26.     void insert(std::initializer_list< value_type > il);

    Effects: inserts each element from the range [il.begin(),il.end()) if and only if there is no element with key equivalent to the key of that element.

    Complexity: At most N log(size()+N) (N is the distance from il.begin() to il.end())

27.     iterator insert(node_type && nh);

    Effects: Inserts a new value move-constructed from x and returns the iterator pointing to the newly inserted element.

    Complexity: Logarithmic.

28.     iterator insert(const_iterator hint, node_type && nh);

    Effects: Inserts a new value move constructed from x in the container. p is a hint pointing to where the insert should start to search.

    Returns: An iterator pointing to the element with key equivalent to the key of x.

    Complexity: Logarithmic in general, but amortized constant if t is inserted right before p.

29.     template<typename C2>
          void merge(multiset< Key, C2, Allocator, Options > & source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

30.     template<typename C2>
          void merge(multiset< Key, C2, Allocator, Options > && source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

31.     template<typename C2> void merge(set< Key, C2, Allocator, Options > & source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

32.     template<typename C2> void merge(set< Key, C2, Allocator, Options > && source);

    Requires: this->get_allocator() == source.get_allocator().

    Effects: Extracts each element in source and insert it into a using the comparison object of *this.

    Postcondition: Pointers and references to the transferred elements of source refer to those same elements but as members of *this. Iterators referring to the transferred elements will continue to refer to their elements, but they now behave as iterators into *this, not into source.

    Throws: Nothing unless the comparison object throws.

    Complexity: N log(size() + N) (N has the value source.size())

33.     iterator erase(const_iterator p);

    Effects: Erases the element pointed to by p.

    Returns: Returns an iterator pointing to the element immediately following q prior to the element being erased. If no such element exists, returns end().

    Complexity: Amortized constant time

34.     size_type erase(const key_type & x);

    Effects: Erases all elements in the container with key equivalent to x.

    Returns: Returns the number of erased elements.

    Complexity: log(size()) + count(k)

35.     iterator erase(const_iterator first, const_iterator last);

    Effects: Erases all the elements in the range [first, last).

    Returns: Returns last.

    Complexity: log(size())+N where N is the distance from first to last.

36.     node_type extract(const_iterator p);

    Effects: Removes the element pointed to by "position".

    Returns: A node_type owning the element, otherwise an empty node_type.

    Complexity: Amortized constant.

37.     node_type extract(const key_type & x);

    Effects: Removes the first element in the container with key equivalent to k.

    Returns: A node_type owning the element if found, otherwise an empty node_type.

    Complexity: log(size()).

38.     void swap(multiset & x) noexcept(allocator_traits_type::is_always_equal::value &&boost::container::dtl::is_nothrow_swappable< Compare >::value));

    Effects: Swaps the contents of *this and x.

    Throws: Nothing.

    Complexity: Constant.

39.     void clear() noexcept;

    Effects: erase(begin(),end()).

    Postcondition: size() == 0.

    Complexity: linear in size().

40.     key_compare key_comp() const;

    Effects: Returns the comparison object out of which a was constructed.

    Complexity: Constant.

41.     value_compare value_comp() const;

    Effects: Returns an object of value_compare constructed out of the comparison object.

    Complexity: Constant.

42.     iterator find(const key_type & x);

    Returns: An iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

43.     const_iterator find(const key_type & x) const;

    Returns: A const_iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

44.     template<typename K> iterator find(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: An iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

45.     template<typename K> const_iterator find(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: An iterator pointing to an element with the key equivalent to x, or end() if such an element is not found.

    Complexity: Logarithmic.

46.     size_type count(const key_type & x) const;

    Returns: The number of elements with key equivalent to x.

    Complexity: log(size())+count(k)

47.     template<typename K> size_type count(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: The number of elements with key equivalent to x.

    Complexity: log(size())+count(k)

48.     bool contains(const key_type & x) const;

    Returns: Returns true if there is an element with key equivalent to key in the container, otherwise false.

    Complexity: log(size()).

49.     template<typename K> bool contains(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: Returns true if there is an element with key equivalent to key in the container, otherwise false.

    Complexity: log(size()).

50.     iterator lower_bound(const key_type & x);

    Returns: An iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

51.     const_iterator lower_bound(const key_type & x) const;

    Returns: A const iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

52.     template<typename K> iterator lower_bound(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: An iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

53.     template<typename K> const_iterator lower_bound(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: A const iterator pointing to the first element with key not less than x, or end() if such an element is not found.

    Complexity: Logarithmic

54.     iterator upper_bound(const key_type & x);

    Returns: An iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

55.     const_iterator upper_bound(const key_type & x) const;

    Returns: A const iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

56.     template<typename K> iterator upper_bound(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: An iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

57.     template<typename K> const_iterator upper_bound(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Returns: A const iterator pointing to the first element with key greater than x, or end() if such an element is not found.

    Complexity: Logarithmic

58.     std::pair< const_iterator, const_iterator >
        equal_range(const key_type & x) const;

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

59.     std::pair< iterator, iterator > equal_range(const key_type & x);

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

60.     template<typename K>
          std::pair< const_iterator, const_iterator > equal_range(const K & x) const;

    Requires: This overload is available only if key_compare::is_transparent exists.

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

61.     template<typename K> std::pair< iterator, iterator > equal_range(const K & x);

    Requires: This overload is available only if key_compare::is_transparent exists.

    Effects: Equivalent to std::make_pair(this->lower_bound(k), this->upper_bound(k)).

    Complexity: Logarithmic

62.     void rebalance();

    Effects: Rebalances the tree. It's a no-op for Red-Black and AVL trees.

    Complexity: Linear

### `multiset` friend functions

1.     friend bool operator==(const multiset & x, const multiset & y);

   Effects: Returns true if x and y are equal

   Complexity: Linear to the number of elements in the container.

2.     friend bool operator!=(const multiset & x, const multiset & y);

   Effects: Returns true if x and y are unequal

   Complexity: Linear to the number of elements in the container.

3.     friend bool operator<(const multiset & x, const multiset & y);

   Effects: Returns true if x is less than y

   Complexity: Linear to the number of elements in the container.

4.     friend bool operator>(const multiset & x, const multiset & y);

   Effects: Returns true if x is greater than y

   Complexity: Linear to the number of elements in the container.

5.     friend bool operator<=(const multiset & x, const multiset & y);

   Effects: Returns true if x is equal or less than y

   Complexity: Linear to the number of elements in the container.

6.     friend bool operator>=(const multiset & x, const multiset & y);

   Effects: Returns true if x is equal or greater than y

   Complexity: Linear to the number of elements in the container.

7.     friend void swap(multiset & x, multiset & y);

   Effects: x.swap(y)

   Complexity: Constant.