text: // Copyright 2018 The Abseil Authors.
  //
  // Licensed under the Apache License, Version 2.0 (the "License");
  // you may not use this file except in compliance with the License.
  // You may obtain a copy of the License at
  //
  //      https://www.apache.org/licenses/LICENSE-2.0
  //
  // Unless required by applicable law or agreed to in writing, software
  // distributed under the License is distributed on an "AS IS" BASIS,
  // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  // See the License for the specific language governing permissions and
  // limitations under the License.
  //
  // -----------------------------------------------------------------------------
  // File: btree_set.h
  // -----------------------------------------------------------------------------
  //
  // This header file defines B-tree sets: sorted associative containers of
  // values.
  //
  //     * `absl::btree_set<>`
  //     * `absl::btree_multiset<>`
  //
  // These B-tree types are similar to the corresponding types in the STL
  // (`std::set` and `std::multiset`) and generally conform to the STL interfaces
  // of those types. However, because they are implemented using B-trees, they
  // are more efficient in most situations.
  //
  // Unlike `std::set` and `std::multiset`, which are commonly implemented using
  // red-black tree nodes, B-tree sets use more generic B-tree nodes able to hold
  // multiple values per node. Holding multiple values per node often makes
  // B-tree sets perform better than their `std::set` counterparts, because
  // multiple entries can be checked within the same cache hit.
  //
  // However, these types should not be considered drop-in replacements for
  // `std::set` and `std::multiset` as there are some API differences, which are
  // noted in this header file.
  //
  // Importantly, insertions and deletions may invalidate outstanding iterators,
  // pointers, and references to elements. Such invalidations are typically only
  // an issue if insertion and deletion operations are interleaved with the use of
  // more than one iterator, pointer, or reference simultaneously. For this
  // reason, `insert()` and `erase()` return a valid iterator at the current
  // position.
  
  #ifndef ABSL_CONTAINER_BTREE_SET_H_
  #define ABSL_CONTAINER_BTREE_SET_H_
  
  #include "absl/container/internal/btree.h"  // IWYU pragma: export
  #include "absl/container/internal/btree_container.h"  // IWYU pragma: export
  
  namespace absl {
  ABSL_NAMESPACE_BEGIN
  
  // absl::btree_set<>
  //
  // An `absl::btree_set<K>` is an ordered associative container of unique key
  // values designed to be a more efficient replacement for `std::set` (in most
  // cases).
  //
  // Keys are sorted using an (optional) comparison function, which defaults to
  // `std::less<K>`.
  //
  // An `absl::btree_set<K>` uses a default allocator of `std::allocator<K>` to
  // allocate (and deallocate) nodes, and construct and destruct values within
  // those nodes. You may instead specify a custom allocator `A` (which in turn
  // requires specifying a custom comparator `C`) as in
  // `absl::btree_set<K, C, A>`.
  //
  template <typename Key, typename Compare = std::less<Key>,
            typename Alloc = std::allocator<Key>>
  class btree_set
      : public container_internal::btree_set_container<
            container_internal::btree<container_internal::set_params<
                Key, Compare, Alloc, /*TargetNodeSize=*/256,
                /*Multi=*/false>>> {
    using Base = typename btree_set::btree_set_container;
  
   public:
    // Constructors and Assignment Operators
    //
    // A `btree_set` supports the same overload set as `std::set`
    // for construction and assignment:
    //
    // * Default constructor
    //
    //   absl::btree_set<std::string> set1;
    //
    // * Initializer List constructor
    //
    //   absl::btree_set<std::string> set2 =
    //       {{"huey"}, {"dewey"}, {"louie"},};
    //
    // * Copy constructor
    //
    //   absl::btree_set<std::string> set3(set2);
    //
    // * Copy assignment operator
    //
    //  absl::btree_set<std::string> set4;
    //  set4 = set3;
    //
    // * Move constructor
    //
    //   // Move is guaranteed efficient
    //   absl::btree_set<std::string> set5(std::move(set4));
    //
    // * Move assignment operator
    //
    //   // May be efficient if allocators are compatible
    //   absl::btree_set<std::string> set6;
    //   set6 = std::move(set5);
    //
    // * Range constructor
    //
    //   std::vector<std::string> v = {"a", "b"};
    //   absl::btree_set<std::string> set7(v.begin(), v.end());
    btree_set() {}
    using Base::Base;
  
    // btree_set::begin()
    //
    // Returns an iterator to the beginning of the `btree_set`.
    using Base::begin;
  
    // btree_set::cbegin()
    //
    // Returns a const iterator to the beginning of the `btree_set`.
    using Base::cbegin;
  
    // btree_set::end()
    //
    // Returns an iterator to the end of the `btree_set`.
    using Base::end;
  
    // btree_set::cend()
    //
    // Returns a const iterator to the end of the `btree_set`.
    using Base::cend;
  
    // btree_set::empty()
    //
    // Returns whether or not the `btree_set` is empty.
    using Base::empty;
  
    // btree_set::max_size()
    //
    // Returns the largest theoretical possible number of elements within a
    // `btree_set` under current memory constraints. This value can be thought
    // of as the largest value of `std::distance(begin(), end())` for a
    // `btree_set<Key>`.
    using Base::max_size;
  
    // btree_set::size()
    //
    // Returns the number of elements currently within the `btree_set`.
    using Base::size;
  
    // btree_set::clear()
    //
    // Removes all elements from the `btree_set`. Invalidates any references,
    // pointers, or iterators referring to contained elements.
    using Base::clear;
  
    // btree_set::erase()
    //
    // Erases elements within the `btree_set`. Overloads are listed below.
    //
    // iterator erase(iterator position):
    // iterator erase(const_iterator position):
    //
    //   Erases the element at `position` of the `btree_set`, returning
    //   the iterator pointing to the element after the one that was erased
    //   (or end() if none exists).
    //
    // iterator erase(const_iterator first, const_iterator last):
    //
    //   Erases the elements in the open interval [`first`, `last`), returning
    //   the iterator pointing to the element after the interval that was erased
    //   (or end() if none exists).
    //
    // template <typename K> size_type erase(const K& key):
    //
    //   Erases the element with the matching key, if it exists, returning the
    //   number of elements erased (0 or 1).
    using Base::erase;
  
    // btree_set::insert()
    //
    // Inserts an element of the specified value into the `btree_set`,
    // returning an iterator pointing to the newly inserted element, provided that
    // an element with the given key does not already exist. If an insertion
    // occurs, any references, pointers, or iterators are invalidated.
    // Overloads are listed below.
    //
    // std::pair<iterator,bool> insert(const value_type& value):
    //
    //   Inserts a value into the `btree_set`. Returns a pair consisting of an
    //   iterator to the inserted element (or to the element that prevented the
    //   insertion) and a bool denoting whether the insertion took place.
    //
    // std::pair<iterator,bool> insert(value_type&& value):
    //
    //   Inserts a moveable value into the `btree_set`. Returns a pair
    //   consisting of an iterator to the inserted element (or to the element that
    //   prevented the insertion) and a bool denoting whether the insertion took
    //   place.
    //
    // iterator insert(const_iterator hint, const value_type& value):
    // iterator insert(const_iterator hint, value_type&& value):
    //
    //   Inserts a value, using the position of `hint` as a non-binding suggestion
    //   for where to begin the insertion search. Returns an iterator to the
    //   inserted element, or to the existing element that prevented the
    //   insertion.
    //
    // void insert(InputIterator first, InputIterator last):
    //
    //   Inserts a range of values [`first`, `last`).
    //
    // void insert(std::initializer_list<init_type> ilist):
    //
    //   Inserts the elements within the initializer list `ilist`.
    using Base::insert;
  
    // btree_set::emplace()
    //
    // Inserts an element of the specified value by constructing it in-place
    // within the `btree_set`, provided that no element with the given key
    // already exists.
    //
    // The element may be constructed even if there already is an element with the
    // key in the container, in which case the newly constructed element will be
    // destroyed immediately.
    //
    // If an insertion occurs, any references, pointers, or iterators are
    // invalidated.
    using Base::emplace;
  
    // btree_set::emplace_hint()
    //
    // Inserts an element of the specified value by constructing it in-place
    // within the `btree_set`, using the position of `hint` as a non-binding
    // suggestion for where to begin the insertion search, and only inserts
    // provided that no element with the given key already exists.
    //
    // The element may be constructed even if there already is an element with the
    // key in the container, in which case the newly constructed element will be
    // destroyed immediately.
    //
    // If an insertion occurs, any references, pointers, or iterators are
    // invalidated.
    using Base::emplace_hint;
  
    // btree_set::extract()
    //
    // Extracts the indicated element, erasing it in the process, and returns it
    // as a C++17-compatible node handle. Overloads are listed below.
    //
    // node_type extract(const_iterator position):
    //
    //   Extracts the element at the indicated position and returns a node handle
    //   owning that extracted data.
    //
    // template <typename K> node_type extract(const K& k):
    //
    //   Extracts the element with the key matching the passed key value and
    //   returns a node handle owning that extracted data. If the `btree_set`
    //   does not contain an element with a matching key, this function returns an
    //   empty node handle.
    //
    // NOTE: In this context, `node_type` refers to the C++17 concept of a
    // move-only type that owns and provides access to the elements in associative
    // containers (https://en.cppreference.com/w/cpp/container/node_handle).
    // It does NOT refer to the data layout of the underlying btree.
    using Base::extract;
  
    // btree_set::merge()
    //
    // Extracts elements from a given `source` btree_set into this
    // `btree_set`. If the destination `btree_set` already contains an
    // element with an equivalent key, that element is not extracted.
    using Base::merge;
  
    // btree_set::swap(btree_set& other)
    //
    // Exchanges the contents of this `btree_set` with those of the `other`
    // btree_set, avoiding invocation of any move, copy, or swap operations on
    // individual elements.
    //
    // All iterators and references on the `btree_set` remain valid, excepting
    // for the past-the-end iterator, which is invalidated.
    using Base::swap;
  
    // btree_set::contains()
    //
    // template <typename K> bool contains(const K& key) const:
    //
    // Determines whether an element comparing equal to the given `key` exists
    // within the `btree_set`, returning `true` if so or `false` otherwise.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::contains;
  
    // btree_set::count()
    //
    // template <typename K> size_type count(const K& key) const:
    //
    // Returns the number of elements comparing equal to the given `key` within
    // the `btree_set`. Note that this function will return either `1` or `0`
    // since duplicate elements are not allowed within a `btree_set`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::count;
  
    // btree_set::equal_range()
    //
    // Returns a closed range [first, last], defined by a `std::pair` of two
    // iterators, containing all elements with the passed key in the
    // `btree_set`.
    using Base::equal_range;
  
    // btree_set::find()
    //
    // template <typename K> iterator find(const K& key):
    // template <typename K> const_iterator find(const K& key) const:
    //
    // Finds an element with the passed `key` within the `btree_set`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::find;
  
    // btree_set::lower_bound()
    //
    // template <typename K> iterator lower_bound(const K& key):
    // template <typename K> const_iterator lower_bound(const K& key) const:
    //
    // Finds the first element that is not less than `key` within the `btree_set`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::lower_bound;
  
    // btree_set::upper_bound()
    //
    // template <typename K> iterator upper_bound(const K& key):
    // template <typename K> const_iterator upper_bound(const K& key) const:
    //
    // Finds the first element that is greater than `key` within the `btree_set`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::upper_bound;
  
    // btree_set::get_allocator()
    //
    // Returns the allocator function associated with this `btree_set`.
    using Base::get_allocator;
  
    // btree_set::key_comp();
    //
    // Returns the key comparator associated with this `btree_set`.
    using Base::key_comp;
  
    // btree_set::value_comp();
    //
    // Returns the value comparator associated with this `btree_set`. The keys to
    // sort the elements are the values themselves, therefore `value_comp` and its
    // sibling member function `key_comp` are equivalent.
    using Base::value_comp;
  };
  
  // absl::swap(absl::btree_set<>, absl::btree_set<>)
  //
  // Swaps the contents of two `absl::btree_set` containers.
  template <typename K, typename C, typename A>
  void swap(btree_set<K, C, A> &x, btree_set<K, C, A> &y) {
    return x.swap(y);
  }
  
  // absl::erase_if(absl::btree_set<>, Pred)
  //
  // Erases all elements that satisfy the predicate pred from the container.
  template <typename K, typename C, typename A, typename Pred>
  void erase_if(btree_set<K, C, A> &set, Pred pred) {
    for (auto it = set.begin(); it != set.end();) {
      if (pred(*it)) {
        it = set.erase(it);
      } else {
        ++it;
      }
    }
  }
  
  // absl::btree_multiset<>
  //
  // An `absl::btree_multiset<K>` is an ordered associative container of
  // keys and associated values designed to be a more efficient replacement
  // for `std::multiset` (in most cases). Unlike `absl::btree_set`, a B-tree
  // multiset allows equivalent elements.
  //
  // Keys are sorted using an (optional) comparison function, which defaults to
  // `std::less<K>`.
  //
  // An `absl::btree_multiset<K>` uses a default allocator of `std::allocator<K>`
  // to allocate (and deallocate) nodes, and construct and destruct values within
  // those nodes. You may instead specify a custom allocator `A` (which in turn
  // requires specifying a custom comparator `C`) as in
  // `absl::btree_multiset<K, C, A>`.
  //
  template <typename Key, typename Compare = std::less<Key>,
            typename Alloc = std::allocator<Key>>
  class btree_multiset
      : public container_internal::btree_multiset_container<
            container_internal::btree<container_internal::set_params<
                Key, Compare, Alloc, /*TargetNodeSize=*/256,
                /*Multi=*/true>>> {
    using Base = typename btree_multiset::btree_multiset_container;
  
   public:
    // Constructors and Assignment Operators
    //
    // A `btree_multiset` supports the same overload set as `std::set`
    // for construction and assignment:
    //
    // * Default constructor
    //
    //   absl::btree_multiset<std::string> set1;
    //
    // * Initializer List constructor
    //
    //   absl::btree_multiset<std::string> set2 =
    //       {{"huey"}, {"dewey"}, {"louie"},};
    //
    // * Copy constructor
    //
    //   absl::btree_multiset<std::string> set3(set2);
    //
    // * Copy assignment operator
    //
    //  absl::btree_multiset<std::string> set4;
    //  set4 = set3;
    //
    // * Move constructor
    //
    //   // Move is guaranteed efficient
    //   absl::btree_multiset<std::string> set5(std::move(set4));
    //
    // * Move assignment operator
    //
    //   // May be efficient if allocators are compatible
    //   absl::btree_multiset<std::string> set6;
    //   set6 = std::move(set5);
    //
    // * Range constructor
    //
    //   std::vector<std::string> v = {"a", "b"};
    //   absl::btree_multiset<std::string> set7(v.begin(), v.end());
    btree_multiset() {}
    using Base::Base;
  
    // btree_multiset::begin()
    //
    // Returns an iterator to the beginning of the `btree_multiset`.
    using Base::begin;
  
    // btree_multiset::cbegin()
    //
    // Returns a const iterator to the beginning of the `btree_multiset`.
    using Base::cbegin;
  
    // btree_multiset::end()
    //
    // Returns an iterator to the end of the `btree_multiset`.
    using Base::end;
  
    // btree_multiset::cend()
    //
    // Returns a const iterator to the end of the `btree_multiset`.
    using Base::cend;
  
    // btree_multiset::empty()
    //
    // Returns whether or not the `btree_multiset` is empty.
    using Base::empty;
  
    // btree_multiset::max_size()
    //
    // Returns the largest theoretical possible number of elements within a
    // `btree_multiset` under current memory constraints. This value can be
    // thought of as the largest value of `std::distance(begin(), end())` for a
    // `btree_multiset<Key>`.
    using Base::max_size;
  
    // btree_multiset::size()
    //
    // Returns the number of elements currently within the `btree_multiset`.
    using Base::size;
  
    // btree_multiset::clear()
    //
    // Removes all elements from the `btree_multiset`. Invalidates any references,
    // pointers, or iterators referring to contained elements.
    using Base::clear;
  
    // btree_multiset::erase()
    //
    // Erases elements within the `btree_multiset`. Overloads are listed below.
    //
    // iterator erase(iterator position):
    // iterator erase(const_iterator position):
    //
    //   Erases the element at `position` of the `btree_multiset`, returning
    //   the iterator pointing to the element after the one that was erased
    //   (or end() if none exists).
    //
    // iterator erase(const_iterator first, const_iterator last):
    //
    //   Erases the elements in the open interval [`first`, `last`), returning
    //   the iterator pointing to the element after the interval that was erased
    //   (or end() if none exists).
    //
    // template <typename K> size_type erase(const K& key):
    //
    //   Erases the elements matching the key, if any exist, returning the
    //   number of elements erased.
    using Base::erase;
  
    // btree_multiset::insert()
    //
    // Inserts an element of the specified value into the `btree_multiset`,
    // returning an iterator pointing to the newly inserted element.
    // Any references, pointers, or iterators are invalidated.  Overloads are
    // listed below.
    //
    // iterator insert(const value_type& value):
    //
    //   Inserts a value into the `btree_multiset`, returning an iterator to the
    //   inserted element.
    //
    // iterator insert(value_type&& value):
    //
    //   Inserts a moveable value into the `btree_multiset`, returning an iterator
    //   to the inserted element.
    //
    // iterator insert(const_iterator hint, const value_type& value):
    // iterator insert(const_iterator hint, value_type&& value):
    //
    //   Inserts a value, using the position of `hint` as a non-binding suggestion
    //   for where to begin the insertion search. Returns an iterator to the
    //   inserted element.
    //
    // void insert(InputIterator first, InputIterator last):
    //
    //   Inserts a range of values [`first`, `last`).
    //
    // void insert(std::initializer_list<init_type> ilist):
    //
    //   Inserts the elements within the initializer list `ilist`.
    using Base::insert;
  
    // btree_multiset::emplace()
    //
    // Inserts an element of the specified value by constructing it in-place
    // within the `btree_multiset`. Any references, pointers, or iterators are
    // invalidated.
    using Base::emplace;
  
    // btree_multiset::emplace_hint()
    //
    // Inserts an element of the specified value by constructing it in-place
    // within the `btree_multiset`, using the position of `hint` as a non-binding
    // suggestion for where to begin the insertion search.
    //
    // Any references, pointers, or iterators are invalidated.
    using Base::emplace_hint;
  
    // btree_multiset::extract()
    //
    // Extracts the indicated element, erasing it in the process, and returns it
    // as a C++17-compatible node handle. Overloads are listed below.
    //
    // node_type extract(const_iterator position):
    //
    //   Extracts the element at the indicated position and returns a node handle
    //   owning that extracted data.
    //
    // template <typename K> node_type extract(const K& k):
    //
    //   Extracts the element with the key matching the passed key value and
    //   returns a node handle owning that extracted data. If the `btree_multiset`
    //   does not contain an element with a matching key, this function returns an
    //   empty node handle.
    //
    // NOTE: In this context, `node_type` refers to the C++17 concept of a
    // move-only type that owns and provides access to the elements in associative
    // containers (https://en.cppreference.com/w/cpp/container/node_handle).
    // It does NOT refer to the data layout of the underlying btree.
    using Base::extract;
  
    // btree_multiset::merge()
    //
    // Extracts all elements from a given `source` btree_multiset into this
    // `btree_multiset`.
    using Base::merge;
  
    // btree_multiset::swap(btree_multiset& other)
    //
    // Exchanges the contents of this `btree_multiset` with those of the `other`
    // btree_multiset, avoiding invocation of any move, copy, or swap operations
    // on individual elements.
    //
    // All iterators and references on the `btree_multiset` remain valid,
    // excepting for the past-the-end iterator, which is invalidated.
    using Base::swap;
  
    // btree_multiset::contains()
    //
    // template <typename K> bool contains(const K& key) const:
    //
    // Determines whether an element comparing equal to the given `key` exists
    // within the `btree_multiset`, returning `true` if so or `false` otherwise.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::contains;
  
    // btree_multiset::count()
    //
    // template <typename K> size_type count(const K& key) const:
    //
    // Returns the number of elements comparing equal to the given `key` within
    // the `btree_multiset`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::count;
  
    // btree_multiset::equal_range()
    //
    // Returns a closed range [first, last], defined by a `std::pair` of two
    // iterators, containing all elements with the passed key in the
    // `btree_multiset`.
    using Base::equal_range;
  
    // btree_multiset::find()
    //
    // template <typename K> iterator find(const K& key):
    // template <typename K> const_iterator find(const K& key) const:
    //
    // Finds an element with the passed `key` within the `btree_multiset`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::find;
  
    // btree_multiset::lower_bound()
    //
    // template <typename K> iterator lower_bound(const K& key):
    // template <typename K> const_iterator lower_bound(const K& key) const:
    //
    // Finds the first element that is not less than `key` within the
    // `btree_multiset`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::lower_bound;
  
    // btree_multiset::upper_bound()
    //
    // template <typename K> iterator upper_bound(const K& key):
    // template <typename K> const_iterator upper_bound(const K& key) const:
    //
    // Finds the first element that is greater than `key` within the
    // `btree_multiset`.
    //
    // Supports heterogeneous lookup, provided that the set has a compatible
    // heterogeneous comparator.
    using Base::upper_bound;
  
    // btree_multiset::get_allocator()
    //
    // Returns the allocator function associated with this `btree_multiset`.
    using Base::get_allocator;
  
    // btree_multiset::key_comp();
    //
    // Returns the key comparator associated with this `btree_multiset`.
    using Base::key_comp;
  
    // btree_multiset::value_comp();
    //
    // Returns the value comparator associated with this `btree_multiset`. The
    // keys to sort the elements are the values themselves, therefore `value_comp`
    // and its sibling member function `key_comp` are equivalent.
    using Base::value_comp;
  };
  
  // absl::swap(absl::btree_multiset<>, absl::btree_multiset<>)
  //
  // Swaps the contents of two `absl::btree_multiset` containers.
  template <typename K, typename C, typename A>
  void swap(btree_multiset<K, C, A> &x, btree_multiset<K, C, A> &y) {
    return x.swap(y);
  }
  
  // absl::erase_if(absl::btree_multiset<>, Pred)
  //
  // Erases all elements that satisfy the predicate pred from the container.
  template <typename K, typename C, typename A, typename Pred>
  void erase_if(btree_multiset<K, C, A> &set, Pred pred) {
    for (auto it = set.begin(); it != set.end();) {
      if (pred(*it)) {
        it = set.erase(it);
      } else {
        ++it;
      }
    }
  }
  
  ABSL_NAMESPACE_END
  }  // namespace absl
  
  #endif  // ABSL_CONTAINER_BTREE_SET_H_
  