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## Class template multiset

boost::container::multiset

## Synopsis

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

    template<typename T, typename Pred = std::less<T>,
             typename A = std::allocator<T> >
    class multiset {
    public:
      // types
      typedef tree_t::key_type               key_type;
      typedef tree_t::value_type             value_type;
      typedef tree_t::pointer                pointer;
      typedef tree_t::const_pointer          const_pointer;
      typedef tree_t::reference              reference;
      typedef tree_t::const_reference        const_reference;
      typedef Pred                           key_compare;
      typedef Pred                           value_compare;
      typedef tree_t::iterator               iterator;
      typedef tree_t::const_iterator         const_iterator;
      typedef tree_t::reverse_iterator       reverse_iterator;
      typedef tree_t::const_reverse_iterator const_reverse_iterator;
      typedef tree_t::size_type              size_type;
      typedef tree_t::difference_type        difference_type;
      typedef tree_t::allocator_type         allocator_type;
      typedef tree_t::stored_allocator_type  stored_allocator_type;

      // construct/copy/destruct
      multiset();
      explicit multiset(const Pred &, const allocator_type & = allocator_type());
      template<typename InputIterator>
        multiset(InputIterator, InputIterator, const Pred & = Pred(),
                 const allocator_type & = allocator_type());
      template<typename InputIterator>
        multiset(ordered_range_t, InputIterator, InputIterator,
                 const Pred & = Pred(),
                 const allocator_type & = allocator_type());
      multiset(const multiset &);
      multiset(BOOST_RV_REF(multiset));
      multiset& operator=(BOOST_COPY_ASSIGN_REF(multiset));
      multiset& operator=(BOOST_RV_REF(multiset));

      // public member functions
      key_compare key_comp() const;
      value_compare value_comp() const;
      allocator_type get_allocator() const;
      const stored_allocator_type & get_stored_allocator() const;
      stored_allocator_type & get_stored_allocator();
      iterator begin();
      const_iterator begin() const;
      iterator end();
      const_iterator end() const;
      reverse_iterator rbegin();
      const_reverse_iterator rbegin() const;
      reverse_iterator rend();
      const_reverse_iterator rend() const;
      const_iterator cbegin() const;
      const_iterator cend() const;
      const_reverse_iterator crbegin() const;
      const_reverse_iterator crend() const;
      bool empty() const;
      size_type size() const;
      size_type max_size() const;
      void swap(multiset &);
      iterator insert(insert_const_ref_type);
      iterator insert(T &);
      template<typename U> iterator insert(const U &, unspecified = 0);
      iterator insert(BOOST_RV_REF(value_type));
      iterator insert(const_iterator, insert_const_ref_type);
      iterator insert(const_iterator, T &);
      template<typename U>
        iterator insert(const_iterator, const U &, unspecified = 0);
      iterator insert(const_iterator, BOOST_RV_REF(value_type));
      template<typename InputIterator> void insert(InputIterator, InputIterator);
      template<class... Args> iterator emplace(Args &&...);
      template<class... Args> iterator emplace_hint(const_iterator, Args &&...);
      iterator erase(const_iterator);
      size_type erase(const key_type &);
      iterator erase(const_iterator, const_iterator);
      void clear();
      iterator find(const key_type &);
      const_iterator find(const key_type &) const;
      size_type count(const key_type &) const;
      iterator lower_bound(const key_type &);
      const_iterator lower_bound(const key_type &) const;
      iterator upper_bound(const key_type &);
      const_iterator upper_bound(const key_type &) const;
      std::pair< iterator, iterator > equal_range(const key_type &);
      std::pair< const_iterator, const_iterator >
      equal_range(const key_type &) const;
    };

## 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.

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

1.     multiset();

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

   Complexity: Constant.

2.     explicit multiset(const Pred & comp,
                         const allocator_type & a = allocator_type());

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

   Complexity: Constant.

3.     template<typename InputIterator>
         multiset(InputIterator first, InputIterator last,
                  const Pred & comp = Pred(),
                  const allocator_type & a = allocator_type());

   Effects: Constructs an empty multiset 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 comp and otherwise N logN, where N is last - first.

4.     template<typename InputIterator>
         multiset(ordered_range_t ordered_range, InputIterator first,
                  InputIterator last, const Pred & comp = Pred(),
                  const allocator_type & a = allocator_type());

   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.

5.     multiset(const multiset & x);

   Effects: Copy constructs a multiset.

   Complexity: Linear in x.size().

6.     multiset(BOOST_RV_REF(multiset) x);

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

   Complexity: Construct.

   Postcondition: x is emptied.

7.     multiset& operator=(BOOST_COPY_ASSIGN_REF(multiset) x);

   Effects: Makes *this a copy of x.

   Complexity: Linear in x.size().

8.     multiset& operator=(BOOST_RV_REF(multiset) x);

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

   Complexity: Constant.

### `multiset` public member functions

1.     key_compare key_comp() const;

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

   Complexity: Constant.

2.     value_compare value_comp() const;

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

   Complexity: Constant.

3.     allocator_type get_allocator() const;

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

   Complexity: Constant.

4.     const stored_allocator_type & get_stored_allocator() const;

5.     stored_allocator_type & get_stored_allocator();

6.     iterator begin();

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

   Throws: Nothing.

   Complexity: Constant.

7.     const_iterator begin() const;

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

   Throws: Nothing.

   Complexity: Constant.

8.     iterator end();

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

   Throws: Nothing.

   Complexity: Constant.

9.     const_iterator end() const;

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

   Throws: Nothing.

   Complexity: Constant.

10.     reverse_iterator rbegin();

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

    Throws: Nothing.

    Complexity: Constant.

11.     const_reverse_iterator rbegin() const;

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

    Throws: Nothing.

    Complexity: Constant.

12.     reverse_iterator rend();

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

    Throws: Nothing.

    Complexity: Constant.

13.     const_reverse_iterator rend() const;

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

    Throws: Nothing.

    Complexity: Constant.

14.     const_iterator cbegin() const;

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

    Throws: Nothing.

    Complexity: Constant.

15.     const_iterator cend() const;

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

    Throws: Nothing.

    Complexity: Constant.

16.     const_reverse_iterator crbegin() const;

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

    Throws: Nothing.

    Complexity: Constant.

17.     const_reverse_iterator crend() const;

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

    Throws: Nothing.

    Complexity: Constant.

18.     bool empty() const;

    Effects: Returns true if the container contains no elements.

    Throws: Nothing.

    Complexity: Constant.

19.     size_type size() const;

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

    Throws: Nothing.

    Complexity: Constant.

20.     size_type max_size() const;

    Effects: Returns the largest possible size of the container.

    Throws: Nothing.

    Complexity: Constant.

21.     void swap(multiset & x);

    Effects: Swaps the contents of *this and x.

    Throws: Nothing.

    Complexity: Constant.

22.     iterator insert(insert_const_ref_type x);

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

    Complexity: Logarithmic.

23.     iterator insert(T & x);

24.     template<typename U> iterator insert(const U & u, unspecified = 0);

25.     iterator insert(BOOST_RV_REF(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.

26.     iterator insert(const_iterator p, insert_const_ref_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.

27.     iterator insert(const_iterator position, T & x);

28.     template<typename U>
          iterator insert(const_iterator position, const U & u, unspecified = 0);

29.     iterator insert(const_iterator p, BOOST_RV_REF(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.

30.     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)

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

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

    Complexity: Logarithmic.

32.     template<class... Args>
          iterator emplace_hint(const_iterator hint, Args &&... args);

    Effects: Inserts an object of type T 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.

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.     void clear();

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

    Postcondition: size() == 0.

    Complexity: linear in size().

37.     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.

38.     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.

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

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

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

40.     iterator lower_bound(const key_type & x);

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

    Complexity: Logarithmic

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

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

    Complexity: Logarithmic

42.     iterator upper_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

43.     const_iterator upper_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

44.     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

45.     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