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 // 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: flat_hash_set.h
 // -----------------------------------------------------------------------------
 //
 // An `absl::flat_hash_set<T>` is an unordered associative container designed to
 // be a more efficient replacement for `std::unordered_set`. Like
 // `unordered_set`, search, insertion, and deletion of set elements can be done
 // as an `O(1)` operation. However, `flat_hash_set` (and other unordered
 // associative containers known as the collection of Abseil "Swiss tables")
 // contain other optimizations that result in both memory and computation
 // advantages.
 //
 // In most cases, your default choice for a hash set should be a set of type
 // `flat_hash_set`.
 //
 // `flat_hash_set` is not exception-safe.
 
 #ifndef ABSL_CONTAINER_FLAT_HASH_SET_H_
 #define ABSL_CONTAINER_FLAT_HASH_SET_H_
 
 #include <cstddef>
 #include <memory>
 #include <type_traits>
 #include <utility>
 
 #include "absl/algorithm/container.h"
 #include "absl/base/attributes.h"
 #include "absl/base/macros.h"
 #include "absl/container/hash_container_defaults.h"
 #include "absl/container/internal/container_memory.h"
 #include "absl/container/internal/raw_hash_set.h"  // IWYU pragma: export
 #include "absl/memory/memory.h"
 #include "absl/meta/type_traits.h"
 
 namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace container_internal {
 template <typename T>
 struct FlatHashSetPolicy;
 }  // namespace container_internal
 
 // -----------------------------------------------------------------------------
 // absl::flat_hash_set
 // -----------------------------------------------------------------------------
 //
 // An `absl::flat_hash_set<T>` is an unordered associative container which has
 // been optimized for both speed and memory footprint in most common use cases.
 // Its interface is similar to that of `std::unordered_set<T>` with the
 // following notable differences:
 //
 // * Requires keys that are CopyConstructible
 // * Supports heterogeneous lookup, through `find()` and `insert()`, provided
 //   that the set is provided a compatible heterogeneous hashing function and
 //   equality operator. See below for details.
 // * Invalidates any references and pointers to elements within the table after
 //   `rehash()` and when the table is moved.
 // * Contains a `capacity()` member function indicating the number of element
 //   slots (open, deleted, and empty) within the hash set.
 // * Returns `void` from the `erase(iterator)` overload.
 //
 // By default, `flat_hash_set` uses the `absl::Hash` hashing framework. All
 // fundamental and Abseil types that support the `absl::Hash` framework have a
 // compatible equality operator for comparing insertions into `flat_hash_set`.
 // If your type is not yet supported by the `absl::Hash` framework, see
 // absl/hash/hash.h for information on extending Abseil hashing to user-defined
 // types.
 //
 // Using `absl::flat_hash_set` at interface boundaries in dynamically loaded
 // libraries (e.g. .dll, .so) is unsupported due to way `absl::Hash` values may
 // be randomized across dynamically loaded libraries.
 //
 // To achieve heterogeneous lookup for custom types either `Hash` and `Eq` type
 // parameters can be used or `T` should have public inner types
 // `absl_container_hash` and (optionally) `absl_container_eq`. In either case,
 // `typename Hash::is_transparent` and `typename Eq::is_transparent` should be
 // well-formed. Both types are basically functors:
 // * `Hash` should support `size_t operator()(U val) const` that returns a hash
 // for the given `val`.
 // * `Eq` should support `bool operator()(U lhs, V rhs) const` that returns true
 // if `lhs` is equal to `rhs`.
 //
 // In most cases `T` needs only to provide the `absl_container_hash`. In this
 // case `std::equal_to<void>` will be used instead of `eq` part.
 //
 // NOTE: A `flat_hash_set` stores its keys directly inside its implementation
 // array to avoid memory indirection. Because a `flat_hash_set` is designed to
 // move data when rehashed, set keys will not retain pointer stability. If you
 // require pointer stability, consider using
 // `absl::flat_hash_set<std::unique_ptr<T>>`. If your type is not moveable and
 // you require pointer stability, consider `absl::node_hash_set` instead.
 //
 // Example:
 //
 //   // Create a flat hash set of three strings
 //   absl::flat_hash_set<std::string> ducks =
 //     {"huey", "dewey", "louie"};
 //
 //  // Insert a new element into the flat hash set
 //  ducks.insert("donald");
 //
 //  // Force a rehash of the flat hash set
 //  ducks.rehash(0);
 //
 //  // See if "dewey" is present
 //  if (ducks.contains("dewey")) {
 //    std::cout << "We found dewey!" << std::endl;
 //  }
 template <class T, class Hash = DefaultHashContainerHash<T>,
           class Eq = DefaultHashContainerEq<T>,
           class Allocator = std::allocator<T>>
 class ABSL_INTERNAL_ATTRIBUTE_OWNER flat_hash_set
     : public absl::container_internal::raw_hash_set<
           absl::container_internal::FlatHashSetPolicy<T>, Hash, Eq, Allocator> {
   using Base = typename flat_hash_set::raw_hash_set;
 
  public:
   // Constructors and Assignment Operators
   //
   // A flat_hash_set supports the same overload set as `std::unordered_set`
   // for construction and assignment:
   //
   // *  Default constructor
   //
   //    // No allocation for the table's elements is made.
   //    absl::flat_hash_set<std::string> set1;
   //
   // * Initializer List constructor
   //
   //   absl::flat_hash_set<std::string> set2 =
   //       {{"huey"}, {"dewey"}, {"louie"},};
   //
   // * Copy constructor
   //
   //   absl::flat_hash_set<std::string> set3(set2);
   //
   // * Copy assignment operator
   //
   //  // Hash functor and Comparator are copied as well
   //  absl::flat_hash_set<std::string> set4;
   //  set4 = set3;
   //
   // * Move constructor
   //
   //   // Move is guaranteed efficient
   //   absl::flat_hash_set<std::string> set5(std::move(set4));
   //
   // * Move assignment operator
   //
   //   // May be efficient if allocators are compatible
   //   absl::flat_hash_set<std::string> set6;
   //   set6 = std::move(set5);
   //
   // * Range constructor
   //
   //   std::vector<std::string> v = {"a", "b"};
   //   absl::flat_hash_set<std::string> set7(v.begin(), v.end());
   flat_hash_set() {}
   using Base::Base;
 
   // flat_hash_set::begin()
   //
   // Returns an iterator to the beginning of the `flat_hash_set`.
   using Base::begin;
 
   // flat_hash_set::cbegin()
   //
   // Returns a const iterator to the beginning of the `flat_hash_set`.
   using Base::cbegin;
 
   // flat_hash_set::cend()
   //
   // Returns a const iterator to the end of the `flat_hash_set`.
   using Base::cend;
 
   // flat_hash_set::end()
   //
   // Returns an iterator to the end of the `flat_hash_set`.
   using Base::end;
 
   // flat_hash_set::capacity()
   //
   // Returns the number of element slots (assigned, deleted, and empty)
   // available within the `flat_hash_set`.
   //
   // NOTE: this member function is particular to `absl::flat_hash_set` and is
   // not provided in the `std::unordered_set` API.
   using Base::capacity;
 
   // flat_hash_set::empty()
   //
   // Returns whether or not the `flat_hash_set` is empty.
   using Base::empty;
 
   // flat_hash_set::max_size()
   //
   // Returns the largest theoretical possible number of elements within a
   // `flat_hash_set` under current memory constraints. This value can be thought
   // of the largest value of `std::distance(begin(), end())` for a
   // `flat_hash_set<T>`.
   using Base::max_size;
 
   // flat_hash_set::size()
   //
   // Returns the number of elements currently within the `flat_hash_set`.
   using Base::size;
 
   // flat_hash_set::clear()
   //
   // Removes all elements from the `flat_hash_set`. Invalidates any references,
   // pointers, or iterators referring to contained elements.
   //
   // NOTE: this operation may shrink the underlying buffer. To avoid shrinking
   // the underlying buffer call `erase(begin(), end())`.
   using Base::clear;
 
   // flat_hash_set::erase()
   //
   // Erases elements within the `flat_hash_set`. Erasing does not trigger a
   // rehash. Overloads are listed below.
   //
   // void erase(const_iterator pos):
   //
   //   Erases the element at `position` of the `flat_hash_set`, returning
   //   `void`.
   //
   //   NOTE: returning `void` in this case is different than that of STL
   //   containers in general and `std::unordered_set` in particular (which
   //   return an iterator to the element following the erased element). If that
   //   iterator is needed, simply post increment the iterator:
   //
   //     set.erase(it++);
   //
   // iterator erase(const_iterator first, const_iterator last):
   //
   //   Erases the elements in the open interval [`first`, `last`), returning an
   //   iterator pointing to `last`. The special case of calling
   //   `erase(begin(), end())` resets the reserved growth such that if
   //   `reserve(N)` has previously been called and there has been no intervening
   //   call to `clear()`, then after calling `erase(begin(), end())`, it is safe
   //   to assume that inserting N elements will not cause a rehash.
   //
   // size_type erase(const key_type& key):
   //
   //   Erases the element with the matching key, if it exists, returning the
   //   number of elements erased (0 or 1).
   using Base::erase;
 
   // flat_hash_set::insert()
   //
   // Inserts an element of the specified value into the `flat_hash_set`,
   // returning an iterator pointing to the newly inserted element, provided that
   // an element with the given key does not already exist. If rehashing occurs
   // due to the insertion, all iterators are invalidated. Overloads are listed
   // below.
   //
   // std::pair<iterator,bool> insert(const T& value):
   //
   //   Inserts a value into the `flat_hash_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(T&& value):
   //
   //   Inserts a moveable value into the `flat_hash_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 T& value):
   // iterator insert(const_iterator hint, T&& 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`).
   //
   //   NOTE: Although the STL does not specify which element may be inserted if
   //   multiple keys compare equivalently, for `flat_hash_set` we guarantee the
   //   first match is inserted.
   //
   // void insert(std::initializer_list<T> ilist):
   //
   //   Inserts the elements within the initializer list `ilist`.
   //
   //   NOTE: Although the STL does not specify which element may be inserted if
   //   multiple keys compare equivalently within the initializer list, for
   //   `flat_hash_set` we guarantee the first match is inserted.
   using Base::insert;
 
   // flat_hash_set::emplace()
   //
   // Inserts an element of the specified value by constructing it in-place
   // within the `flat_hash_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 rehashing occurs due to the insertion, all iterators are invalidated.
   using Base::emplace;
 
   // flat_hash_set::emplace_hint()
   //
   // Inserts an element of the specified value by constructing it in-place
   // within the `flat_hash_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 rehashing occurs due to the insertion, all iterators are invalidated.
   using Base::emplace_hint;
 
   // flat_hash_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.
   //
   // node_type extract(const key_type& x):
   //
   //   Extracts the element with the key matching the passed key value and
   //   returns a node handle owning that extracted data. If the `flat_hash_set`
   //   does not contain an element with a matching key, this function returns an
   //   empty node handle.
   using Base::extract;
 
   // flat_hash_set::merge()
   //
   // Extracts elements from a given `source` flat hash set into this
   // `flat_hash_set`. If the destination `flat_hash_set` already contains an
   // element with an equivalent key, that element is not extracted.
   using Base::merge;
 
   // flat_hash_set::swap(flat_hash_set& other)
   //
   // Exchanges the contents of this `flat_hash_set` with those of the `other`
   // flat hash set, avoiding invocation of any move, copy, or swap operations on
   // individual elements.
   //
   // All iterators and references on the `flat_hash_set` remain valid, excepting
   // for the past-the-end iterator, which is invalidated.
   //
   // `swap()` requires that the flat hash set's hashing and key equivalence
   // functions be Swappable, and are exchanged using unqualified calls to
   // non-member `swap()`. If the set's allocator has
   // `std::allocator_traits<allocator_type>::propagate_on_container_swap::value`
   // set to `true`, the allocators are also exchanged using an unqualified call
   // to non-member `swap()`; otherwise, the allocators are not swapped.
   using Base::swap;
 
   // flat_hash_set::rehash(count)
   //
   // Rehashes the `flat_hash_set`, setting the number of slots to be at least
   // the passed value. If the new number of slots increases the load factor more
   // than the current maximum load factor
   // (`count` < `size()` / `max_load_factor()`), then the new number of slots
   // will be at least `size()` / `max_load_factor()`.
   //
   // To force a rehash, pass rehash(0).
   //
   // NOTE: unlike behavior in `std::unordered_set`, references are also
   // invalidated upon a `rehash()`.
   using Base::rehash;
 
   // flat_hash_set::reserve(count)
   //
   // Sets the number of slots in the `flat_hash_set` to the number needed to
   // accommodate at least `count` total elements without exceeding the current
   // maximum load factor, and may rehash the container if needed.
   using Base::reserve;
 
   // flat_hash_set::contains()
   //
   // Determines whether an element comparing equal to the given `key` exists
   // within the `flat_hash_set`, returning `true` if so or `false` otherwise.
   using Base::contains;
 
   // flat_hash_set::count(const Key& key) const
   //
   // Returns the number of elements comparing equal to the given `key` within
   // the `flat_hash_set`. note that this function will return either `1` or `0`
   // since duplicate elements are not allowed within a `flat_hash_set`.
   using Base::count;
 
   // flat_hash_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
   // `flat_hash_set`.
   using Base::equal_range;
 
   // flat_hash_set::find()
   //
   // Finds an element with the passed `key` within the `flat_hash_set`.
   using Base::find;
 
   // flat_hash_set::bucket_count()
   //
   // Returns the number of "buckets" within the `flat_hash_set`. Note that
   // because a flat hash set contains all elements within its internal storage,
   // this value simply equals the current capacity of the `flat_hash_set`.
   using Base::bucket_count;
 
   // flat_hash_set::load_factor()
   //
   // Returns the current load factor of the `flat_hash_set` (the average number
   // of slots occupied with a value within the hash set).
   using Base::load_factor;
 
   // flat_hash_set::max_load_factor()
   //
   // Manages the maximum load factor of the `flat_hash_set`. Overloads are
   // listed below.
   //
   // float flat_hash_set::max_load_factor()
   //
   //   Returns the current maximum load factor of the `flat_hash_set`.
   //
   // void flat_hash_set::max_load_factor(float ml)
   //
   //   Sets the maximum load factor of the `flat_hash_set` to the passed value.
   //
   //   NOTE: This overload is provided only for API compatibility with the STL;
   //   `flat_hash_set` will ignore any set load factor and manage its rehashing
   //   internally as an implementation detail.
   using Base::max_load_factor;
 
   // flat_hash_set::get_allocator()
   //
   // Returns the allocator function associated with this `flat_hash_set`.
   using Base::get_allocator;
 
   // flat_hash_set::hash_function()
   //
   // Returns the hashing function used to hash the keys within this
   // `flat_hash_set`.
   using Base::hash_function;
 
   // flat_hash_set::key_eq()
   //
   // Returns the function used for comparing keys equality.
   using Base::key_eq;
 };
 
 // erase_if(flat_hash_set<>, Pred)
 //
 // Erases all elements that satisfy the predicate `pred` from the container `c`.
 // Returns the number of erased elements.
 template <typename T, typename H, typename E, typename A, typename Predicate>
 typename flat_hash_set<T, H, E, A>::size_type erase_if(
     flat_hash_set<T, H, E, A>& c, Predicate pred) {
   return container_internal::EraseIf(pred, &c);
 }
 
 namespace container_internal {
 
 // c_for_each_fast(flat_hash_set<>, Function)
 //
 // Container-based version of the <algorithm> `std::for_each()` function to
 // apply a function to a container's elements.
 // There is no guarantees on the order of the function calls.
 // Erasure and/or insertion of elements in the function is not allowed.
 template <typename T, typename H, typename E, typename A, typename Function>
 decay_t<Function> c_for_each_fast(const flat_hash_set<T, H, E, A>& c,
                                   Function&& f) {
   container_internal::ForEach(f, &c);
   return f;
 }
 template <typename T, typename H, typename E, typename A, typename Function>
 decay_t<Function> c_for_each_fast(flat_hash_set<T, H, E, A>& c, Function&& f) {
   container_internal::ForEach(f, &c);
   return f;
 }
 template <typename T, typename H, typename E, typename A, typename Function>
 decay_t<Function> c_for_each_fast(flat_hash_set<T, H, E, A>&& c, Function&& f) {
   container_internal::ForEach(f, &c);
   return f;
 }
 
 }  // namespace container_internal
 
 namespace container_internal {
 
 template <class T>
 struct FlatHashSetPolicy {
   using slot_type = T;
   using key_type = T;
   using init_type = T;
   using constant_iterators = std::true_type;
 
   template <class Allocator, class... Args>
   static void construct(Allocator* alloc, slot_type* slot, Args&&... args) {
     absl::allocator_traits<Allocator>::construct(*alloc, slot,
                                                  std::forward<Args>(args)...);
   }
 
   // Return std::true_type in case destroy is trivial.
   template <class Allocator>
   static auto destroy(Allocator* alloc, slot_type* slot) {
     absl::allocator_traits<Allocator>::destroy(*alloc, slot);
     return IsDestructionTrivial<Allocator, slot_type>();
   }
 
   static T& element(slot_type* slot) { return *slot; }
 
   template <class F, class... Args>
   static decltype(absl::container_internal::DecomposeValue(
       std::declval<F>(), std::declval<Args>()...))
   apply(F&& f, Args&&... args) {
     return absl::container_internal::DecomposeValue(
         std::forward<F>(f), std::forward<Args>(args)...);
   }
 
   static size_t space_used(const T*) { return 0; }
 
   template <class Hash>
   static constexpr HashSlotFn get_hash_slot_fn() {
     return &TypeErasedApplyToSlotFn<Hash, T>;
   }
 };
 }  // namespace container_internal
 
 namespace container_algorithm_internal {
 
 // Specialization of trait in absl/algorithm/container.h
 template <class Key, class Hash, class KeyEqual, class Allocator>
 struct IsUnorderedContainer<absl::flat_hash_set<Key, Hash, KeyEqual, Allocator>>
     : std::true_type {};
 
 }  // namespace container_algorithm_internal
 
 ABSL_NAMESPACE_END
 }  // namespace absl
 
 #endif  // ABSL_CONTAINER_FLAT_HASH_SET_H_

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