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1//===----------------------------------------------------------------------===//2//3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.4// See https://llvm.org/LICENSE.txt for license information.5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception6//7//===----------------------------------------------------------------------===//8 9#ifndef _LIBCPP___ALGORITHM_SET_INTERSECTION_H10#define _LIBCPP___ALGORITHM_SET_INTERSECTION_H11 12#include <__algorithm/comp.h>13#include <__algorithm/comp_ref_type.h>14#include <__algorithm/iterator_operations.h>15#include <__algorithm/lower_bound.h>16#include <__config>17#include <__functional/identity.h>18#include <__iterator/iterator_traits.h>19#include <__iterator/next.h>20#include <__type_traits/is_same.h>21#include <__utility/exchange.h>22#include <__utility/forward.h>23#include <__utility/move.h>24#include <__utility/swap.h>25 26#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)27# pragma GCC system_header28#endif29 30_LIBCPP_PUSH_MACROS31#include <__undef_macros>32 33_LIBCPP_BEGIN_NAMESPACE_STD34 35template <class _InIter1, class _InIter2, class _OutIter>36struct __set_intersection_result {37 _InIter1 __in1_;38 _InIter2 __in2_;39 _OutIter __out_;40 41 // need a constructor as C++03 aggregate init is hard42 _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX2043 __set_intersection_result(_InIter1&& __in_iter1, _InIter2&& __in_iter2, _OutIter&& __out_iter)44 : __in1_(std::move(__in_iter1)), __in2_(std::move(__in_iter2)), __out_(std::move(__out_iter)) {}45};46 47// Helper for __set_intersection() with one-sided binary search: populate result and advance input iterators if they48// are found to potentially contain the same value in two consecutive calls. This function is very intimately related to49// the way it is used and doesn't attempt to abstract that, it's not appropriate for general usage outside of its50// context.51template <class _InForwardIter1, class _InForwardIter2, class _OutIter>52_LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __set_intersection_add_output_if_equal(53 bool __may_be_equal,54 _InForwardIter1& __first1,55 _InForwardIter2& __first2,56 _OutIter& __result,57 bool& __prev_may_be_equal) {58 if (__may_be_equal && __prev_may_be_equal) {59 *__result = *__first1;60 ++__result;61 ++__first1;62 ++__first2;63 __prev_may_be_equal = false;64 } else {65 __prev_may_be_equal = __may_be_equal;66 }67}68 69// With forward iterators we can make multiple passes over the data, allowing the use of one-sided binary search to70// reduce best-case complexity to log(N). Understanding how we can use binary search and still respect complexity71// guarantees is _not_ straightforward: the guarantee is "at most 2*(N+M)-1 comparisons", and one-sided binary search72// will necessarily overshoot depending on the position of the needle in the haystack -- for instance, if we're73// searching for 3 in (1, 2, 3, 4), we'll check if 3<1, then 3<2, then 3<4, and, finally, 3<3, for a total of 474// comparisons, when linear search would have yielded 3. However, because we won't need to perform the intervening75// reciprocal comparisons (ie 1<3, 2<3, 4<3), that extra comparison doesn't run afoul of the guarantee. Additionally,76// this type of scenario can only happen for match distances of up to 5 elements, because 2*log2(8) is 6, and we'll77// still be worse-off at position 5 of an 8-element set. From then onwards these scenarios can't happen. TL;DR: we'll be78// 1 comparison worse-off compared to the classic linear-searching algorithm if matching position 3 of a set with 479// elements, or position 5 if the set has 7 or 8 elements, but we'll never exceed the complexity guarantees from the80// standard.81template <class _AlgPolicy,82 class _Compare,83 class _InForwardIter1,84 class _Sent1,85 class _InForwardIter2,86 class _Sent2,87 class _OutIter>88[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI89_LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>90__set_intersection(91 _InForwardIter1 __first1,92 _Sent1 __last1,93 _InForwardIter2 __first2,94 _Sent2 __last2,95 _OutIter __result,96 _Compare&& __comp,97 std::forward_iterator_tag,98 std::forward_iterator_tag) {99 _LIBCPP_CONSTEXPR std::__identity __proj;100 bool __prev_may_be_equal = false;101 102 while (__first2 != __last2) {103 _InForwardIter1 __first1_next =104 std::__lower_bound_onesided<_AlgPolicy>(__first1, __last1, *__first2, __comp, __proj);105 std::swap(__first1_next, __first1);106 // keeping in mind that a==b iff !(a<b) && !(b<a):107 // if we can't advance __first1, that means !(*__first1 < *_first2), therefore __may_be_equal==true108 std::__set_intersection_add_output_if_equal(109 __first1 == __first1_next, __first1, __first2, __result, __prev_may_be_equal);110 if (__first1 == __last1)111 break;112 113 _InForwardIter2 __first2_next =114 std::__lower_bound_onesided<_AlgPolicy>(__first2, __last2, *__first1, __comp, __proj);115 std::swap(__first2_next, __first2);116 std::__set_intersection_add_output_if_equal(117 __first2 == __first2_next, __first1, __first2, __result, __prev_may_be_equal);118 }119 return __set_intersection_result<_InForwardIter1, _InForwardIter2, _OutIter>(120 _IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),121 _IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),122 std::move(__result));123}124 125// input iterators are not suitable for multipass algorithms, so we stick to the classic single-pass version126template <class _AlgPolicy,127 class _Compare,128 class _InInputIter1,129 class _Sent1,130 class _InInputIter2,131 class _Sent2,132 class _OutIter>133[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI134_LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>135__set_intersection(136 _InInputIter1 __first1,137 _Sent1 __last1,138 _InInputIter2 __first2,139 _Sent2 __last2,140 _OutIter __result,141 _Compare&& __comp,142 std::input_iterator_tag,143 std::input_iterator_tag) {144 while (__first1 != __last1 && __first2 != __last2) {145 if (__comp(*__first1, *__first2))146 ++__first1;147 else {148 if (!__comp(*__first2, *__first1)) {149 *__result = *__first1;150 ++__result;151 ++__first1;152 }153 ++__first2;154 }155 }156 157 return __set_intersection_result<_InInputIter1, _InInputIter2, _OutIter>(158 _IterOps<_AlgPolicy>::next(std::move(__first1), std::move(__last1)),159 _IterOps<_AlgPolicy>::next(std::move(__first2), std::move(__last2)),160 std::move(__result));161}162 163template <class _AlgPolicy, class _Compare, class _InIter1, class _Sent1, class _InIter2, class _Sent2, class _OutIter>164[[__nodiscard__]] _LIBCPP_HIDE_FROM_ABI165_LIBCPP_CONSTEXPR_SINCE_CXX20 __set_intersection_result<_InIter1, _InIter2, _OutIter>166__set_intersection(167 _InIter1 __first1, _Sent1 __last1, _InIter2 __first2, _Sent2 __last2, _OutIter __result, _Compare&& __comp) {168 return std::__set_intersection<_AlgPolicy>(169 std::move(__first1),170 std::move(__last1),171 std::move(__first2),172 std::move(__last2),173 std::move(__result),174 std::forward<_Compare>(__comp),175 typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter1>(),176 typename std::_IterOps<_AlgPolicy>::template __iterator_category<_InIter2>());177}178 179template <class _InputIterator1, class _InputIterator2, class _OutputIterator, class _Compare>180inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator set_intersection(181 _InputIterator1 __first1,182 _InputIterator1 __last1,183 _InputIterator2 __first2,184 _InputIterator2 __last2,185 _OutputIterator __result,186 _Compare __comp) {187 return std::__set_intersection<_ClassicAlgPolicy, __comp_ref_type<_Compare> >(188 std::move(__first1),189 std::move(__last1),190 std::move(__first2),191 std::move(__last2),192 std::move(__result),193 __comp)194 .__out_;195}196 197template <class _InputIterator1, class _InputIterator2, class _OutputIterator>198inline _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 _OutputIterator set_intersection(199 _InputIterator1 __first1,200 _InputIterator1 __last1,201 _InputIterator2 __first2,202 _InputIterator2 __last2,203 _OutputIterator __result) {204 return std::__set_intersection<_ClassicAlgPolicy>(205 std::move(__first1),206 std::move(__last1),207 std::move(__first2),208 std::move(__last2),209 std::move(__result),210 __less<>())211 .__out_;212}213 214_LIBCPP_END_NAMESPACE_STD215 216_LIBCPP_POP_MACROS217 218#endif // _LIBCPP___ALGORITHM_SET_INTERSECTION_H219