115 lines
7.4 KiB
Markdown
115 lines
7.4 KiB
Markdown
[alg.lex.comparison]
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# 26 Algorithms library [[algorithms]](./#algorithms)
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## 26.8 Sorting and related operations [[alg.sorting]](alg.sorting#alg.lex.comparison)
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### 26.8.11 Lexicographical comparison [alg.lex.comparison]
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[ð](#lib:lexicographical_compare)
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`template<class InputIterator1, class InputIterator2>
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constexpr bool
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lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
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InputIterator2 first2, InputIterator2 last2);
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template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2>
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bool
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lexicographical_compare(ExecutionPolicy&& exec,
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ForwardIterator1 first1, ForwardIterator1 last1,
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ForwardIterator2 first2, ForwardIterator2 last2);
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template<class InputIterator1, class InputIterator2, class Compare>
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constexpr bool
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lexicographical_compare(InputIterator1 first1, InputIterator1 last1,
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InputIterator2 first2, InputIterator2 last2,
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Compare comp);
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template<class ExecutionPolicy, class ForwardIterator1, class ForwardIterator2,
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class Compare>
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bool
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lexicographical_compare(ExecutionPolicy&& exec,
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ForwardIterator1 first1, ForwardIterator1 last1,
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ForwardIterator2 first2, ForwardIterator2 last2,
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Compare comp);
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template<[input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_iterator [iterator.concept.input]") I1, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_for [iterator.concept.sentinel]")<I1> S1, [input_iterator](iterator.concept.input#concept:input_iterator "24.3.4.9 Concept input_iterator [iterator.concept.input]") I2, [sentinel_for](iterator.concept.sentinel#concept:sentinel_for "24.3.4.7 Concept sentinel_for [iterator.concept.sentinel]")<I2> S2,
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class Proj1 = identity, class Proj2 = identity,
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[indirect_strict_weak_order](indirectcallable.indirectinvocable#concept:indirect_strict_weak_order "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I1, Proj1>,
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projected<I2, Proj2>> Comp = ranges::less>
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constexpr bool
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ranges::lexicographical_compare(I1 first1, S1 last1, I2 first2, S2 last2,
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Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {});
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template<[input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R1, [input_range](range.refinements#concept:input_range "25.4.6 Other range refinements [range.refinements]") R2, class Proj1 = identity,
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class Proj2 = identity,
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[indirect_strict_weak_order](indirectcallable.indirectinvocable#concept:indirect_strict_weak_order "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R1>, Proj1>,
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projected<iterator_t<R2>, Proj2>> Comp = ranges::less>
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constexpr bool
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ranges::lexicographical_compare(R1&& r1, R2&& r2, Comp comp = {},
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Proj1 proj1 = {}, Proj2 proj2 = {});
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template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_access_iterator [iterator.concept.random.access]") I1, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_sentinel_for [iterator.concept.sizedsentinel]")<I1> S1,
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[random_access_iterator](iterator.concept.random.access#concept:random_access_iterator "24.3.4.13 Concept random_access_iterator [iterator.concept.random.access]") I2, [sized_sentinel_for](iterator.concept.sizedsentinel#concept:sized_sentinel_for "24.3.4.8 Concept sized_sentinel_for [iterator.concept.sizedsentinel]")<I2> S2,
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class Proj1 = identity, class Proj2 = identity,
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[indirect_strict_weak_order](indirectcallable.indirectinvocable#concept:indirect_strict_weak_order "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<I1, Proj1>,
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projected<I2, Proj2>> Comp = ranges::less>
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bool ranges::lexicographical_compare(Ep&& exec, I1 first1, S1 last1, I2 first2, S2 last2,
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Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {});
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template<[execution-policy](algorithms.parallel.defns#concept:execution-policy "26.3.1 Preamble [algorithms.parallel.defns]") Ep, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R1, [sized-random-access-range](range.refinements#concept:sized-random-access-range "25.4.6 Other range refinements [range.refinements]") R2,
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class Proj1 = identity, class Proj2 = identity,
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[indirect_strict_weak_order](indirectcallable.indirectinvocable#concept:indirect_strict_weak_order "24.3.6.3 Indirect callables [indirectcallable.indirectinvocable]")<projected<iterator_t<R1>, Proj1>,
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projected<iterator_t<R2>, Proj2>> Comp = ranges::less>
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bool ranges::lexicographical_compare(Ep&& exec, R1&& r1, R2&& r2, Comp comp = {},
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Proj1 proj1 = {}, Proj2 proj2 = {});
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`
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L11801)
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*Returns*: true if and only if
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the sequence of elements defined by the range [first1, last1)
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is lexicographically less than
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the sequence of elements defined by the range [first2, last2)[.](#1.sentence-1)
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L11808)
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*Complexity*: At most 2 min(last1 - first1, last2 - first2) applications
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of the corresponding comparison and each projection, if any[.](#2.sentence-1)
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L11813)
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*Remarks*: If two sequences have the same number of elements and
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their corresponding elements (if any) are equivalent,
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then neither sequence is lexicographically less than the other[.](#3.sentence-1)
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If one sequence is a proper prefix of the other,
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then the shorter sequence is lexicographically less than the longer sequence[.](#3.sentence-2)
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Otherwise, the lexicographical comparison of the sequences yields
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the same result as the comparison
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of the first corresponding pair of elements that are not equivalent[.](#3.sentence-3)
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L11824)
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[*Example [1](#example-1)*:
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ranges::lexicographical_compare(I1, S1, I2, S2, Comp, Proj1, Proj2) can be implemented as:for (; first1 != last1 && first2 != last2; ++first1, (void)++first2) {if (invoke(comp, invoke(proj1, *first1), invoke(proj2, *first2))) return true; if (invoke(comp, invoke(proj2, *first2), invoke(proj1, *first1))) return false;}return first1 == last1 && first2 != last2;
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â *end example*]
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/algorithms.tex#L11837)
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[*Note [1](#note-1)*:
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An empty sequence is lexicographically less than any non-empty sequence,
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but not less than any empty sequence[.](#5.sentence-1)
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â *end note*]
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