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// unordered_set implementation -*- C++ -*-

// Copyright (C) 2010-2015 Free Software Foundation, Inc.

//

// This file is part of the GNU ISO C++ Library.  This library is free

// software; you can redistribute it and/or modify it under the

// terms of the GNU General Public License as published by the

// Free Software Foundation; either version 3, or (at your option)

// any later version.

// This library is distributed in the hope that it will be useful,

// but WITHOUT ANY WARRANTY; without even the implied warranty of

// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

// GNU General Public License for more details.

// Under Section 7 of GPL version 3, you are granted additional

// permissions described in the GCC Runtime Library Exception, version

// 3.1, as published by the Free Software Foundation.

// You should have received a copy of the GNU General Public License and

// a copy of the GCC Runtime Library Exception along with this program;

// see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see

// .

/** @file bits/unordered_set.h

 *  This is an internal header file, included by other library headers.

 *  Do not attempt to use it directly. @headername{unordered_set}

 */

#ifndef _UNORDERED_SET_H

#define _UNORDERED_SET_H

namespace std _GLIBCXX_VISIBILITY(default)

{

_GLIBCXX_BEGIN_NAMESPACE_CONTAINER

  /// Base types for unordered_set.

  template

    using __uset_traits = __detail::_Hashtable_traits<_Cache, true, true>;

  template

	   typename _Hash = hash<_Value>,

	   typename _Pred = std::equal_to<_Value>,

  	   typename _Alloc = std::allocator<_Value>,

	   typename _Tr = __uset_traits<__cache_default<_Value, _Hash>::value>>

    using __uset_hashtable = _Hashtable<_Value, _Value, _Alloc,

					__detail::_Identity, _Pred, _Hash,

					__detail::_Mod_range_hashing,

					__detail::_Default_ranged_hash,

					__detail::_Prime_rehash_policy, _Tr>;

  /// Base types for unordered_multiset.

  template

    using __umset_traits = __detail::_Hashtable_traits<_Cache, true, false>;

  template

	   typename _Hash = hash<_Value>,

	   typename _Pred = std::equal_to<_Value>,

	   typename _Alloc = std::allocator<_Value>,

	   typename _Tr = __umset_traits<__cache_default<_Value, _Hash>::value>>

    using __umset_hashtable = _Hashtable<_Value, _Value, _Alloc,

					 __detail::_Identity,

					 _Pred, _Hash,

					 __detail::_Mod_range_hashing,

					 __detail::_Default_ranged_hash,

					 __detail::_Prime_rehash_policy, _Tr>;

  /**

   *  @brief A standard container composed of unique keys (containing

   *  at most one of each key value) in which the elements' keys are

   *  the elements themselves.

   *

   *  @ingroup unordered_associative_containers

   *

   *  @tparam  _Value  Type of key objects.

   *  @tparam  _Hash  Hashing function object type, defaults to hash<_Value>.

   *  @tparam _Pred Predicate function object type, defaults to

   *                equal_to<_Value>.

   *

   *  @tparam  _Alloc  Allocator type, defaults to allocator<_Key>.

   *

   *  Meets the requirements of a container, and

   *  unordered associative container

   *

   *  Base is _Hashtable, dispatched at compile time via template

   *  alias __uset_hashtable.

   */

  template

	   class _Hash = hash<_Value>,

	   class _Pred = std::equal_to<_Value>,

	   class _Alloc = std::allocator<_Value> >

    class unordered_set

    {

      typedef __uset_hashtable<_Value, _Hash, _Pred, _Alloc>  _Hashtable;

      _Hashtable _M_h;

    public:

      // typedefs:

      //@{

      /// Public typedefs.

      typedef typename _Hashtable::key_type	key_type;

      typedef typename _Hashtable::value_type	value_type;

      typedef typename _Hashtable::hasher	hasher;

      typedef typename _Hashtable::key_equal	key_equal;

      typedef typename _Hashtable::allocator_type allocator_type;

      //@}

      //@{

      ///  Iterator-related typedefs.

      typedef typename _Hashtable::pointer		pointer;

      typedef typename _Hashtable::const_pointer	const_pointer;

      typedef typename _Hashtable::reference		reference;

      typedef typename _Hashtable::const_reference	const_reference;

      typedef typename _Hashtable::iterator		iterator;

      typedef typename _Hashtable::const_iterator	const_iterator;

      typedef typename _Hashtable::local_iterator	local_iterator;

      typedef typename _Hashtable::const_local_iterator	const_local_iterator;

      typedef typename _Hashtable::size_type		size_type;

      typedef typename _Hashtable::difference_type	difference_type;

      //@}

      // construct/destroy/copy

      /// Default constructor.

      unordered_set() = default;

      /**

       *  @brief  Default constructor creates no elements.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param __a  An allocator object.

       */

      explicit

      unordered_set(size_type __n,

		    const hasher& __hf = hasher(),

		    const key_equal& __eql = key_equal(),

		    const allocator_type& __a = allocator_type())

      : _M_h(__n, __hf, __eql, __a)

      { }

      /**

       *  @brief  Builds an %unordered_set from a range.

       *  @param  __first  An input iterator.

       *  @param  __last  An input iterator.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param __a  An allocator object.

       *

       *  Create an %unordered_set consisting of copies of the elements from

       *  [__first,__last).  This is linear in N (where N is

       *  distance(__first,__last)).

       */

      template

	unordered_set(_InputIterator __first, _InputIterator __last,

		      size_type __n = 0,

		      const hasher& __hf = hasher(),

		      const key_equal& __eql = key_equal(),

		      const allocator_type& __a = allocator_type())

	: _M_h(__first, __last, __n, __hf, __eql, __a)

	{ }

      /// Copy constructor.

      unordered_set(const unordered_set&) = default;

      /// Move constructor.

      unordered_set(unordered_set&&) = default;

      /**

       *  @brief Creates an %unordered_set with no elements.

       *  @param __a An allocator object.

       */

      explicit

      unordered_set(const allocator_type& __a)

      : _M_h(__a)

      { }

      /*

       *  @brief Copy constructor with allocator argument.

       * @param  __uset  Input %unordered_set to copy.

       * @param  __a  An allocator object.

       */

      unordered_set(const unordered_set& __uset,

		    const allocator_type& __a)

      : _M_h(__uset._M_h, __a)

      { }

      /*

       *  @brief  Move constructor with allocator argument.

       *  @param  __uset Input %unordered_set to move.

       *  @param  __a    An allocator object.

       */

      unordered_set(unordered_set&& __uset,

		    const allocator_type& __a)

      : _M_h(std::move(__uset._M_h), __a)

      { }

      /**

       *  @brief  Builds an %unordered_set from an initializer_list.

       *  @param  __l  An initializer_list.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param  __a  An allocator object.

       *

       *  Create an %unordered_set consisting of copies of the elements in the

       *  list. This is linear in N (where N is @a __l.size()).

       */

      unordered_set(initializer_list __l,

		    size_type __n = 0,

		    const hasher& __hf = hasher(),

		    const key_equal& __eql = key_equal(),

		    const allocator_type& __a = allocator_type())

      : _M_h(__l, __n, __hf, __eql, __a)

      { }

      unordered_set(size_type __n, const allocator_type& __a)

      : unordered_set(__n, hasher(), key_equal(), __a)

      { }

      unordered_set(size_type __n, const hasher& __hf,

		    const allocator_type& __a)

      : unordered_set(__n, __hf, key_equal(), __a)

      { }

      template

	unordered_set(_InputIterator __first, _InputIterator __last,

		      size_type __n,

		      const allocator_type& __a)

	: unordered_set(__first, __last, __n, hasher(), key_equal(), __a)

	{ }

      template

	unordered_set(_InputIterator __first, _InputIterator __last,

		      size_type __n, const hasher& __hf,

		      const allocator_type& __a)

	: unordered_set(__first, __last, __n, __hf, key_equal(), __a)

	{ }

      unordered_set(initializer_list __l,

		    size_type __n,

		    const allocator_type& __a)

      : unordered_set(__l, __n, hasher(), key_equal(), __a)

      { }

      unordered_set(initializer_list __l,

		    size_type __n, const hasher& __hf,

		    const allocator_type& __a)

      : unordered_set(__l, __n, __hf, key_equal(), __a)

      { }

      /// Copy assignment operator.

      unordered_set&

      operator=(const unordered_set&) = default;

      /// Move assignment operator.

      unordered_set&

      operator=(unordered_set&&) = default;

      /**

       *  @brief  %Unordered_set list assignment operator.

       *  @param  __l  An initializer_list.

       *

       *  This function fills an %unordered_set with copies of the elements in

       *  the initializer list @a __l.

       *

       *  Note that the assignment completely changes the %unordered_set and

       *  that the resulting %unordered_set's size is the same as the number

       *  of elements assigned.  Old data may be lost.

       */

      unordered_set&

      operator=(initializer_list __l)

      {

	_M_h = __l;

	return *this;

      }

      ///  Returns the allocator object with which the %unordered_set was

      ///  constructed.

      allocator_type

      get_allocator() const noexcept

      { return _M_h.get_allocator(); }

      // size and capacity:

      ///  Returns true if the %unordered_set is empty.

      bool

      empty() const noexcept

      { return _M_h.empty(); }

      ///  Returns the size of the %unordered_set.

      size_type

      size() const noexcept

      { return _M_h.size(); }

      ///  Returns the maximum size of the %unordered_set.

      size_type

      max_size() const noexcept

      { return _M_h.max_size(); }

      // iterators.

      //@{

      /**

       *  Returns a read-only (constant) iterator that points to the first

       *  element in the %unordered_set.

       */

      iterator

      begin() noexcept

      { return _M_h.begin(); }

      const_iterator

      begin() const noexcept

      { return _M_h.begin(); }

      //@}

      //@{

      /**

       *  Returns a read-only (constant) iterator that points one past the last

       *  element in the %unordered_set.

       */

      iterator

      end() noexcept

      { return _M_h.end(); }

      const_iterator

      end() const noexcept

      { return _M_h.end(); }

      //@}

      /**

       *  Returns a read-only (constant) iterator that points to the first

       *  element in the %unordered_set.

       */

      const_iterator

      cbegin() const noexcept

      { return _M_h.begin(); }

      /**

       *  Returns a read-only (constant) iterator that points one past the last

       *  element in the %unordered_set.

       */

      const_iterator

      cend() const noexcept

      { return _M_h.end(); }

      // modifiers.

      /**

       *  @brief Attempts to build and insert an element into the

       *  %unordered_set.

       *  @param __args  Arguments used to generate an element.

       *  @return  A pair, of which the first element is an iterator that points

       *           to the possibly inserted element, and the second is a bool

       *           that is true if the element was actually inserted.

       *

       *  This function attempts to build and insert an element into the

       *  %unordered_set. An %unordered_set relies on unique keys and thus an

       *  element is only inserted if it is not already present in the

       *  %unordered_set.

       *

       *  Insertion requires amortized constant time.

       */

      template

	std::pair

	emplace(_Args&&... __args)

	{ return _M_h.emplace(std::forward<_Args>(__args)...); }

      /**

       *  @brief Attempts to insert an element into the %unordered_set.

       *  @param  __pos  An iterator that serves as a hint as to where the

       *                element should be inserted.

       *  @param  __args  Arguments used to generate the element to be

       *                 inserted.

       *  @return An iterator that points to the element with key equivalent to

       *          the one generated from @a __args (may or may not be the

       *          element itself).

       *

       *  This function is not concerned about whether the insertion took place,

       *  and thus does not return a boolean like the single-argument emplace()

       *  does.  Note that the first parameter is only a hint and can

       *  potentially improve the performance of the insertion process.  A bad

       *  hint would cause no gains in efficiency.

       *

       *  For more on @a hinting, see:

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *

       *  Insertion requires amortized constant time.

       */

      template

	iterator

	emplace_hint(const_iterator __pos, _Args&&... __args)

	{ return _M_h.emplace_hint(__pos, std::forward<_Args>(__args)...); }

      //@{

      /**

       *  @brief Attempts to insert an element into the %unordered_set.

       *  @param  __x  Element to be inserted.

       *  @return  A pair, of which the first element is an iterator that points

       *           to the possibly inserted element, and the second is a bool

       *           that is true if the element was actually inserted.

       *

       *  This function attempts to insert an element into the %unordered_set.

       *  An %unordered_set relies on unique keys and thus an element is only

       *  inserted if it is not already present in the %unordered_set.

       *

       *  Insertion requires amortized constant time.

       */

      std::pair

      insert(const value_type& __x)

      { return _M_h.insert(__x); }

      std::pair

      insert(value_type&& __x)

      { return _M_h.insert(std::move(__x)); }

      //@}

      //@{

      /**

       *  @brief Attempts to insert an element into the %unordered_set.

       *  @param  __hint  An iterator that serves as a hint as to where the

       *                 element should be inserted.

       *  @param  __x  Element to be inserted.

       *  @return An iterator that points to the element with key of

       *           @a __x (may or may not be the element passed in).

       *

       *  This function is not concerned about whether the insertion took place,

       *  and thus does not return a boolean like the single-argument insert()

       *  does.  Note that the first parameter is only a hint and can

       *  potentially improve the performance of the insertion process.  A bad

       *  hint would cause no gains in efficiency.

       *

       *  For more on @a hinting, see:

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *

       *  Insertion requires amortized constant.

       */

      iterator

      insert(const_iterator __hint, const value_type& __x)

      { return _M_h.insert(__hint, __x); }

      iterator

      insert(const_iterator __hint, value_type&& __x)

      { return _M_h.insert(__hint, std::move(__x)); }

      //@}

      /**

       *  @brief A template function that attempts to insert a range of

       *  elements.

       *  @param  __first  Iterator pointing to the start of the range to be

       *                   inserted.

       *  @param  __last  Iterator pointing to the end of the range.

       *

       *  Complexity similar to that of the range constructor.

       */

      template

	void

	insert(_InputIterator __first, _InputIterator __last)

	{ _M_h.insert(__first, __last); }

      /**

       *  @brief Attempts to insert a list of elements into the %unordered_set.

       *  @param  __l  A std::initializer_list of elements

       *               to be inserted.

       *

       *  Complexity similar to that of the range constructor.

       */

      void

      insert(initializer_list __l)

      { _M_h.insert(__l); }

      //@{

      /**

       *  @brief Erases an element from an %unordered_set.

       *  @param  __position  An iterator pointing to the element to be erased.

       *  @return An iterator pointing to the element immediately following

       *          @a __position prior to the element being erased. If no such

       *          element exists, end() is returned.

       *

       *  This function erases an element, pointed to by the given iterator,

       *  from an %unordered_set.  Note that this function only erases the

       *  element, and that if the element is itself a pointer, the pointed-to

       *  memory is not touched in any way.  Managing the pointer is the user's

       *  responsibility.

       */

      iterator

      erase(const_iterator __position)

      { return _M_h.erase(__position); }

      // LWG 2059.

      iterator

      erase(iterator __position)

      { return _M_h.erase(__position); }

      //@}

      /**

       *  @brief Erases elements according to the provided key.

       *  @param  __x  Key of element to be erased.

       *  @return  The number of elements erased.

       *

       *  This function erases all the elements located by the given key from

       *  an %unordered_set. For an %unordered_set the result of this function

       *  can only be 0 (not present) or 1 (present).

       *  Note that this function only erases the element, and that if

       *  the element is itself a pointer, the pointed-to memory is not touched

       *  in any way.  Managing the pointer is the user's responsibility.

       */

      size_type

      erase(const key_type& __x)

      { return _M_h.erase(__x); }

      /**

       *  @brief Erases a [__first,__last) range of elements from an

       *  %unordered_set.

       *  @param  __first  Iterator pointing to the start of the range to be

       *                  erased.

       *  @param __last  Iterator pointing to the end of the range to

       *                be erased.

       *  @return The iterator @a __last.

       *

       *  This function erases a sequence of elements from an %unordered_set.

       *  Note that this function only erases the element, and that if

       *  the element is itself a pointer, the pointed-to memory is not touched

       *  in any way.  Managing the pointer is the user's responsibility.

       */

      iterator

      erase(const_iterator __first, const_iterator __last)

      { return _M_h.erase(__first, __last); }

      /**

       *  Erases all elements in an %unordered_set. Note that this function only

       *  erases the elements, and that if the elements themselves are pointers,

       *  the pointed-to memory is not touched in any way. Managing the pointer

       *  is the user's responsibility.

       */

      void

      clear() noexcept

      { _M_h.clear(); }

      /**

       *  @brief  Swaps data with another %unordered_set.

       *  @param  __x  An %unordered_set of the same element and allocator

       *  types.

       *

       *  This exchanges the elements between two sets in constant time.

       *  Note that the global std::swap() function is specialized such that

       *  std::swap(s1,s2) will feed to this function.

       */

      void

      swap(unordered_set& __x)

      noexcept( noexcept(_M_h.swap(__x._M_h)) )

      { _M_h.swap(__x._M_h); }

      // observers.

      ///  Returns the hash functor object with which the %unordered_set was

      ///  constructed.

      hasher

      hash_function() const

      { return _M_h.hash_function(); }

      ///  Returns the key comparison object with which the %unordered_set was

      ///  constructed.

      key_equal

      key_eq() const

      { return _M_h.key_eq(); }

      // lookup.

      //@{

      /**

       *  @brief Tries to locate an element in an %unordered_set.

       *  @param  __x  Element to be located.

       *  @return  Iterator pointing to sought-after element, or end() if not

       *           found.

       *

       *  This function takes a key and tries to locate the element with which

       *  the key matches.  If successful the function returns an iterator

       *  pointing to the sought after element.  If unsuccessful it returns the

       *  past-the-end ( @c end() ) iterator.

       */

      iterator

      find(const key_type& __x)

      { return _M_h.find(__x); }

      const_iterator

      find(const key_type& __x) const

      { return _M_h.find(__x); }

      //@}

      /**

       *  @brief  Finds the number of elements.

       *  @param  __x  Element to located.

       *  @return  Number of elements with specified key.

       *

       *  This function only makes sense for unordered_multisets; for

       *  unordered_set the result will either be 0 (not present) or 1

       *  (present).

       */

      size_type

      count(const key_type& __x) const

      { return _M_h.count(__x); }

      //@{

      /**

       *  @brief Finds a subsequence matching given key.

       *  @param  __x  Key to be located.

       *  @return  Pair of iterators that possibly points to the subsequence

       *           matching given key.

       *

       *  This function probably only makes sense for multisets.

       */

      std::pair

      equal_range(const key_type& __x)

      { return _M_h.equal_range(__x); }

      std::pair

      equal_range(const key_type& __x) const

      { return _M_h.equal_range(__x); }

      //@}

      // bucket interface.

      /// Returns the number of buckets of the %unordered_set.

      size_type

      bucket_count() const noexcept

      { return _M_h.bucket_count(); }

      /// Returns the maximum number of buckets of the %unordered_set.

      size_type

      max_bucket_count() const noexcept

      { return _M_h.max_bucket_count(); }

      /*

       * @brief  Returns the number of elements in a given bucket.

       * @param  __n  A bucket index.

       * @return  The number of elements in the bucket.

       */

      size_type

      bucket_size(size_type __n) const

      { return _M_h.bucket_size(__n); }

      /*

       * @brief  Returns the bucket index of a given element.

       * @param  __key  A key instance.

       * @return  The key bucket index.

       */

      size_type

      bucket(const key_type& __key) const

      { return _M_h.bucket(__key); }

      //@{

      /**

       *  @brief  Returns a read-only (constant) iterator pointing to the first

       *         bucket element.

       *  @param  __n The bucket index.

       *  @return  A read-only local iterator.

       */

      local_iterator

      begin(size_type __n)

      { return _M_h.begin(__n); }

      const_local_iterator

      begin(size_type __n) const

      { return _M_h.begin(__n); }

      const_local_iterator

      cbegin(size_type __n) const

      { return _M_h.cbegin(__n); }

      //@}

      //@{

      /**

       *  @brief  Returns a read-only (constant) iterator pointing to one past

       *         the last bucket elements.

       *  @param  __n The bucket index.

       *  @return  A read-only local iterator.

       */

      local_iterator

      end(size_type __n)

      { return _M_h.end(__n); }

      const_local_iterator

      end(size_type __n) const

      { return _M_h.end(__n); }

      const_local_iterator

      cend(size_type __n) const

      { return _M_h.cend(__n); }

      //@}

      // hash policy.

      /// Returns the average number of elements per bucket.

      float

      load_factor() const noexcept

      { return _M_h.load_factor(); }

      /// Returns a positive number that the %unordered_set tries to keep the

      /// load factor less than or equal to.

      float

      max_load_factor() const noexcept

      { return _M_h.max_load_factor(); }

      /**

       *  @brief  Change the %unordered_set maximum load factor.

       *  @param  __z The new maximum load factor.

       */

      void

      max_load_factor(float __z)

      { _M_h.max_load_factor(__z); }

      /**

       *  @brief  May rehash the %unordered_set.

       *  @param  __n The new number of buckets.

       *

       *  Rehash will occur only if the new number of buckets respect the

       *  %unordered_set maximum load factor.

       */

      void

      rehash(size_type __n)

      { _M_h.rehash(__n); }

      /**

       *  @brief  Prepare the %unordered_set for a specified number of

       *          elements.

       *  @param  __n Number of elements required.

       *

       *  Same as rehash(ceil(n / max_load_factor())).

       */

      void

      reserve(size_type __n)

      { _M_h.reserve(__n); }

      template

	       typename _Alloc1>

        friend bool

        operator==(const unordered_set<_Value1, _Hash1, _Pred1, _Alloc1>&,

		   const unordered_set<_Value1, _Hash1, _Pred1, _Alloc1>&);

    };

  /**

   *  @brief A standard container composed of equivalent keys

   *  (possibly containing multiple of each key value) in which the

   *  elements' keys are the elements themselves.

   *

   *  @ingroup unordered_associative_containers

   *

   *  @tparam  _Value  Type of key objects.

   *  @tparam  _Hash  Hashing function object type, defaults to hash<_Value>.

   *  @tparam  _Pred  Predicate function object type, defaults

   *                  to equal_to<_Value>.

   *  @tparam  _Alloc  Allocator type, defaults to allocator<_Key>.

   *

   *  Meets the requirements of a container, and

   *  unordered associative container

   *

   *  Base is _Hashtable, dispatched at compile time via template

   *  alias __umset_hashtable.

   */

  template

	   class _Hash = hash<_Value>,

	   class _Pred = std::equal_to<_Value>,

	   class _Alloc = std::allocator<_Value> >

    class unordered_multiset

    {

      typedef __umset_hashtable<_Value, _Hash, _Pred, _Alloc>  _Hashtable;

      _Hashtable _M_h;

    public:

      // typedefs:

      //@{

      /// Public typedefs.

      typedef typename _Hashtable::key_type	key_type;

      typedef typename _Hashtable::value_type	value_type;

      typedef typename _Hashtable::hasher	hasher;

      typedef typename _Hashtable::key_equal	key_equal;

      typedef typename _Hashtable::allocator_type allocator_type;

      //@}

      //@{

      ///  Iterator-related typedefs.

      typedef typename _Hashtable::pointer		pointer;

      typedef typename _Hashtable::const_pointer	const_pointer;

      typedef typename _Hashtable::reference		reference;

      typedef typename _Hashtable::const_reference	const_reference;

      typedef typename _Hashtable::iterator		iterator;

      typedef typename _Hashtable::const_iterator	const_iterator;

      typedef typename _Hashtable::local_iterator	local_iterator;

      typedef typename _Hashtable::const_local_iterator	const_local_iterator;

      typedef typename _Hashtable::size_type		size_type;

      typedef typename _Hashtable::difference_type	difference_type;

      //@}

      // construct/destroy/copy

      /// Default constructor.

      unordered_multiset() = default;

      /**

       *  @brief  Default constructor creates no elements.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param __a  An allocator object.

       */

      explicit

      unordered_multiset(size_type __n,

			 const hasher& __hf = hasher(),

			 const key_equal& __eql = key_equal(),

			 const allocator_type& __a = allocator_type())

      : _M_h(__n, __hf, __eql, __a)

      { }

      /**

       *  @brief  Builds an %unordered_multiset from a range.

       *  @param  __first  An input iterator.

       *  @param  __last   An input iterator.

       *  @param __n       Minimal initial number of buckets.

       *  @param __hf      A hash functor.

       *  @param __eql     A key equality functor.

       *  @param __a       An allocator object.

       *

       *  Create an %unordered_multiset consisting of copies of the elements

       *  from [__first,__last).  This is linear in N (where N is

       *  distance(__first,__last)).

       */

      template

	unordered_multiset(_InputIterator __first, _InputIterator __last,

			   size_type __n = 0,

			   const hasher& __hf = hasher(),

			   const key_equal& __eql = key_equal(),

			   const allocator_type& __a = allocator_type())

	: _M_h(__first, __last, __n, __hf, __eql, __a)

	{ }

      /// Copy constructor.

      unordered_multiset(const unordered_multiset&) = default;

      /// Move constructor.

      unordered_multiset(unordered_multiset&&) = default;

      /**

       *  @brief  Builds an %unordered_multiset from an initializer_list.

       *  @param  __l  An initializer_list.

       *  @param __n  Minimal initial number of buckets.

       *  @param __hf  A hash functor.

       *  @param __eql  A key equality functor.

       *  @param  __a  An allocator object.

       *

       *  Create an %unordered_multiset consisting of copies of the elements in

       *  the list. This is linear in N (where N is @a __l.size()).

       */

      unordered_multiset(initializer_list __l,

			 size_type __n = 0,

			 const hasher& __hf = hasher(),

			 const key_equal& __eql = key_equal(),

			 const allocator_type& __a = allocator_type())

      : _M_h(__l, __n, __hf, __eql, __a)

      { }

      /// Copy assignment operator.

      unordered_multiset&

      operator=(const unordered_multiset&) = default;

      /// Move assignment operator.

      unordered_multiset&

      operator=(unordered_multiset&&) = default;

      /**

       *  @brief Creates an %unordered_multiset with no elements.

       *  @param __a An allocator object.

       */

      explicit

      unordered_multiset(const allocator_type& __a)

      : _M_h(__a)

      { }

      /*

       *  @brief Copy constructor with allocator argument.

       * @param  __uset  Input %unordered_multiset to copy.

       * @param  __a  An allocator object.

       */

      unordered_multiset(const unordered_multiset& __umset,

			 const allocator_type& __a)

      : _M_h(__umset._M_h, __a)

      { }

      /*

       *  @brief  Move constructor with allocator argument.

       *  @param  __umset  Input %unordered_multiset to move.

       *  @param  __a  An allocator object.

       */

      unordered_multiset(unordered_multiset&& __umset,

			 const allocator_type& __a)

      : _M_h(std::move(__umset._M_h), __a)

      { }

      unordered_multiset(size_type __n, const allocator_type& __a)

      : unordered_multiset(__n, hasher(), key_equal(), __a)

      { }

      unordered_multiset(size_type __n, const hasher& __hf,

			 const allocator_type& __a)

      : unordered_multiset(__n, __hf, key_equal(), __a)

      { }

      template

	unordered_multiset(_InputIterator __first, _InputIterator __last,

			   size_type __n,

			   const allocator_type& __a)

	: unordered_multiset(__first, __last, __n, hasher(), key_equal(), __a)

	{ }

      template

	unordered_multiset(_InputIterator __first, _InputIterator __last,

			   size_type __n, const hasher& __hf,

			   const allocator_type& __a)

	: unordered_multiset(__first, __last, __n, __hf, key_equal(), __a)

	{ }

      unordered_multiset(initializer_list __l,

			 size_type __n,

			 const allocator_type& __a)

      : unordered_multiset(__l, __n, hasher(), key_equal(), __a)

      { }

      unordered_multiset(initializer_list __l,

			 size_type __n, const hasher& __hf,

			 const allocator_type& __a)

      : unordered_multiset(__l, __n, __hf, key_equal(), __a)

      { }

      /**

       *  @brief  %Unordered_multiset list assignment operator.

       *  @param  __l  An initializer_list.

       *

       *  This function fills an %unordered_multiset with copies of the elements

       *  in the initializer list @a __l.

       *

       *  Note that the assignment completely changes the %unordered_multiset

       *  and that the resulting %unordered_multiset's size is the same as the

       *  number of elements assigned. Old data may be lost.

       */

      unordered_multiset&

      operator=(initializer_list __l)

      {

	_M_h = __l;

	return *this;

      }

      ///  Returns the allocator object with which the %unordered_multiset was

      ///  constructed.

      allocator_type

      get_allocator() const noexcept

      { return _M_h.get_allocator(); }

      // size and capacity:

      ///  Returns true if the %unordered_multiset is empty.

      bool

      empty() const noexcept

      { return _M_h.empty(); }

      ///  Returns the size of the %unordered_multiset.

      size_type

      size() const noexcept

      { return _M_h.size(); }

      ///  Returns the maximum size of the %unordered_multiset.

      size_type

      max_size() const noexcept

      { return _M_h.max_size(); }

      // iterators.

      //@{

      /**

       *  Returns a read-only (constant) iterator that points to the first

       *  element in the %unordered_multiset.

       */

      iterator

      begin() noexcept

      { return _M_h.begin(); }

      const_iterator

      begin() const noexcept

      { return _M_h.begin(); }

      //@}

      //@{

      /**

       *  Returns a read-only (constant) iterator that points one past the last

       *  element in the %unordered_multiset.

       */

      iterator

      end() noexcept

      { return _M_h.end(); }

      const_iterator

      end() const noexcept

      { return _M_h.end(); }

      //@}

      /**

       *  Returns a read-only (constant) iterator that points to the first

       *  element in the %unordered_multiset.

       */

      const_iterator

      cbegin() const noexcept

      { return _M_h.begin(); }

      /**

       *  Returns a read-only (constant) iterator that points one past the last

       *  element in the %unordered_multiset.

       */

      const_iterator

      cend() const noexcept

      { return _M_h.end(); }

      // modifiers.

      /**

       *  @brief Builds and insert an element into the %unordered_multiset.

       *  @param __args  Arguments used to generate an element.

       *  @return  An iterator that points to the inserted element.

       *

       *  Insertion requires amortized constant time.

       */

      template

	iterator

	emplace(_Args&&... __args)

	{ return _M_h.emplace(std::forward<_Args>(__args)...); }

      /**

       *  @brief Inserts an element into the %unordered_multiset.

       *  @param  __pos  An iterator that serves as a hint as to where the

       *                element should be inserted.

       *  @param  __args  Arguments used to generate the element to be

       *                 inserted.

       *  @return An iterator that points to the inserted element.

       *

       *  Note that the first parameter is only a hint and can potentially

       *  improve the performance of the insertion process.  A bad hint would

       *  cause no gains in efficiency.

       *

       *  For more on @a hinting, see:

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *

       *  Insertion requires amortized constant time.

       */

      template

	iterator

	emplace_hint(const_iterator __pos, _Args&&... __args)

	{ return _M_h.emplace_hint(__pos, std::forward<_Args>(__args)...); }

      //@{

      /**

       *  @brief Inserts an element into the %unordered_multiset.

       *  @param  __x  Element to be inserted.

       *  @return  An iterator that points to the inserted element.

       *

       *  Insertion requires amortized constant time.

       */

      iterator

      insert(const value_type& __x)

      { return _M_h.insert(__x); }

      iterator

      insert(value_type&& __x)

      { return _M_h.insert(std::move(__x)); }

      //@}

      //@{

      /**

       *  @brief Inserts an element into the %unordered_multiset.

       *  @param  __hint  An iterator that serves as a hint as to where the

       *                 element should be inserted.

       *  @param  __x  Element to be inserted.

       *  @return An iterator that points to the inserted element.

       *

       *  Note that the first parameter is only a hint and can potentially

       *  improve the performance of the insertion process.  A bad hint would

       *  cause no gains in efficiency.

       *

       *  For more on @a hinting, see:

       *  https://gcc.gnu.org/onlinedocs/libstdc++/manual/associative.html#containers.associative.insert_hints

       *

       *  Insertion requires amortized constant.

       */

      iterator

      insert(const_iterator __hint, const value_type& __x)

      { return _M_h.insert(__hint, __x); }

      iterator

      insert(const_iterator __hint, value_type&& __x)

      { return _M_h.insert(__hint, std::move(__x)); }

      //@}

      /**

       *  @brief A template function that inserts a range of elements.

       *  @param  __first  Iterator pointing to the start of the range to be

       *                   inserted.

       *  @param  __last  Iterator pointing to the end of the range.

       *

       *  Complexity similar to that of the range constructor.

       */

      template

	void

	insert(_InputIterator __first, _InputIterator __last)

	{ _M_h.insert(__first, __last); }

      /**

       *  @brief Inserts a list of elements into the %unordered_multiset.

       *  @param  __l  A std::initializer_list of elements to be

       *              inserted.

       *

       *  Complexity similar to that of the range constructor.

       */

      void

      insert(initializer_list __l)

      { _M_h.insert(__l); }