Difference between revisions of "cpp/algorithm/ranges/upper bound"
From cppreference.com
m (FTM.) |
|||
| (7 intermediate revisions by 6 users not shown) | |||
| Line 2: | Line 2: | ||
{{cpp/algorithm/ranges/navbar}} | {{cpp/algorithm/ranges/navbar}} | ||
{{dcl begin}} | {{dcl begin}} | ||
| − | {{dcl header | algorithm}} | + | {{dcl header|algorithm}} |
| − | {{dcl | num=1 | since=c++20 |1= | + | {{dcl h|Call signature}} |
| + | {{dcl rev begin|num=1}} | ||
| + | {{dcla|anchor=1|since=c++20|until=c++26|1= | ||
template< std::forward_iterator I, std::sentinel_for<I> S, | template< std::forward_iterator I, std::sentinel_for<I> S, | ||
class T, class Proj = std::identity, | class T, class Proj = std::identity, | ||
| − | std::indirect_strict_weak_order | + | std::indirect_strict_weak_order |
| − | const T*, | + | <const T*, std::projected<I, Proj>> Comp = ranges::less > |
| − | + | constexpr I upper_bound( I first, S last, const T& value, | |
| − | + | Comp comp = {}, Proj proj = {} ); | |
| − | upper_bound( I first, S last, const T& value, Comp comp = {}, Proj proj = {} ); | + | |
}} | }} | ||
| − | {{dcl | num=2 | since=c++20 |1= | + | {{dcl|since=c++26|1= |
| − | template< ranges::forward_range R, class T, class Proj = std::identity, | + | template< std::forward_iterator I, std::sentinel_for<I> S, |
| − | std::indirect_strict_weak_order | + | class Proj = std::identity, |
| − | const T*, | + | class T = std::projected_value_t<I, Proj>, |
| − | std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less > | + | std::indirect_strict_weak_order |
| − | + | <const T*, std::projected<I, Proj>> Comp = ranges::less > | |
| − | upper_bound( R&& r, const T& value, Comp comp = {}, Proj proj = {} ); | + | constexpr I upper_bound( I first, S last, const T& value, |
| + | Comp comp = {}, Proj proj = {} ); | ||
| + | }} | ||
| + | {{dcl rev end}} | ||
| + | {{dcl rev begin|num=2}} | ||
| + | {{dcl|since=c++20|until=c++26|1= | ||
| + | template< ranges::forward_range R, | ||
| + | class T, class Proj = std::identity, | ||
| + | std::indirect_strict_weak_order | ||
| + | <const T*, std::projected<ranges::iterator_t<R>, | ||
| + | Proj>> Comp = ranges::less > | ||
| + | constexpr ranges::borrowed_iterator_t<R> | ||
| + | upper_bound( R&& r, const T& value, Comp comp = {}, Proj proj = {} ); | ||
| + | }} | ||
| + | {{dcl|since=c++26|1= | ||
| + | template< ranges::forward_range R, | ||
| + | class Proj = std::identity, | ||
| + | class T = std::projected_value_t<ranges::iterator_t<R>, Proj>, | ||
| + | std::indirect_strict_weak_order | ||
| + | <const T*, std::projected<ranges::iterator_t<R>, | ||
| + | Proj>> Comp = ranges::less > | ||
| + | constexpr ranges::borrowed_iterator_t<R> | ||
| + | upper_bound( R&& r, const T& value, Comp comp = {}, Proj proj = {} ); | ||
}} | }} | ||
| + | {{dcl rev end}} | ||
{{dcl end}} | {{dcl end}} | ||
| − | @1@ Returns an iterator pointing to the first element in the range {{ | + | @1@ Returns an iterator pointing to the first element in the range {{range|first|last}} that is ''greater'' than {{c|value}}, or {{c|last}} if no such element is found. |
| − | The range {{ | + | The range {{range|first|last}} must be partitioned with respect to the expression or {{c|!comp(value, element)}}, i.e., all elements for which the expression is {{c|true}} must precede all elements for which the expression is {{c|false}}. A fully-sorted range meets this criterion. |
| − | @2@ Same as {{v|1}}, but uses {{ | + | @2@ Same as {{v|1}}, but uses {{c|r}} as the source range, as if using {{c|ranges::begin(r)}} as {{c|first}} and {{c|ranges::end(r)}} as {{c|last}}. |
{{cpp/ranges/niebloid}} | {{cpp/ranges/niebloid}} | ||
| Line 31: | Line 55: | ||
===Parameters=== | ===Parameters=== | ||
{{par begin}} | {{par begin}} | ||
| − | {{par | first, last | | + | {{par|first, last|iterator-sentinel defining the partially-ordered range to examine}} |
| − | {{par | r | | + | {{par|r|the partially-ordered range to examine}} |
| − | {{par | value | value to compare the elements to}} | + | {{par|value|value to compare the elements to}} |
| − | {{par | pred | predicate to apply to the projected elements}} | + | {{par|pred|predicate to apply to the projected elements}} |
| − | {{par | proj | projection to apply to the elements}} | + | {{par|proj|projection to apply to the elements}} |
{{par end}} | {{par end}} | ||
===Return value=== | ===Return value=== | ||
| − | Iterator pointing to the first element that is ''greater'' than {{ | + | Iterator pointing to the first element that is ''greater'' than {{c|value}}, or {{c|last}} if no such element is found. |
===Complexity=== | ===Complexity=== | ||
| − | The number of comparisons and applications of the projection performed are logarithmic in the distance between {{ | + | The number of comparisons and applications of the projection performed are logarithmic in the distance between {{c|first}} and {{c|last}} (at most {{math|log{{su|b=2}}(last - first) + O(1)}} comparisons and applications of the projection). However, for an iterator that does not model {{lconcept|random_access_iterator}}, the number of iterator increments is linear. |
===Possible implementation=== | ===Possible implementation=== | ||
| − | {{eq fun | + | {{eq fun|1= |
| − | + | struct upper_bound_fn | |
| − | struct upper_bound_fn { | + | { |
| − | + | template<std::forward_iterator I, std::sentinel_for<I> S, | |
| − | + | class Proj = std::identity, class T = std::projected_value_t<I, Proj>, | |
| − | + | std::indirect_strict_weak_order | |
| − | + | <const T*, std::projected<I, Proj>> Comp = ranges::less> | |
| − | + | constexpr I operator()(I first, S last, const T& value, | |
| − | + | Comp comp = {}, Proj proj = {}) const | |
| − | + | { | |
| − | + | I it; | |
| − | + | std::iter_difference_t<I> count, step; | |
| − | + | count = ranges::distance(first, last); | |
| − | + | ||
| − | + | while (count > 0) | |
| − | + | { | |
| − | + | it = first; | |
| − | + | step = count / 2; | |
| − | + | ranges::advance(it, step, last); | |
| − | + | if (!comp(value, std::invoke(proj, *it))) | |
| − | + | { | |
| − | + | first = ++it; | |
| − | + | count -= step + 1; | |
| − | + | } | |
| − | + | else | |
| − | + | count = step; | |
| − | + | } | |
| − | + | return first; | |
| − | + | } | |
| − | + | ||
| − | + | template<ranges::forward_range R, class Proj = std::identity, | |
| − | + | class T = std::projected_value_t<ranges::iterator_t<R>, Proj>, | |
| − | + | std::indirect_strict_weak_order | |
| − | + | <const T*, std::projected<ranges::iterator_t<R>, | |
| − | + | Proj>> Comp = ranges::less> | |
| − | + | constexpr ranges::borrowed_iterator_t<R> | |
| − | + | operator()(R&& r, const T& value, Comp comp = {}, Proj proj = {}) const | |
| − | + | { | |
| − | + | return (*this)(ranges::begin(r), ranges::end(r), value, | |
| − | + | std::ref(comp), std::ref(proj)); | |
| + | } | ||
}; | }; | ||
inline constexpr upper_bound_fn upper_bound; | inline constexpr upper_bound_fn upper_bound; | ||
}} | }} | ||
| + | |||
| + | ===Notes=== | ||
| + | {{feature test macro|__cpp_lib_algorithm_default_value_type|value=202403|std=C++26|[[cpp/language/list initialization|List-initialization]] for algorithms {{vl|1,2}}}} | ||
===Example=== | ===Example=== | ||
{{example | {{example | ||
| − | + | |code= | |
| − | + | ||
#include <algorithm> | #include <algorithm> | ||
| + | #include <cassert> | ||
| + | #include <complex> | ||
#include <iostream> | #include <iostream> | ||
#include <iterator> | #include <iterator> | ||
| Line 101: | Line 130: | ||
int main() | int main() | ||
{ | { | ||
| − | std::vector<int> data | + | namespace ranges = std::ranges; |
| − | + | ||
| + | std::vector<int> data{1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6}; | ||
| + | |||
{ | { | ||
auto lower = ranges::lower_bound(data.begin(), data.end(), 4); | auto lower = ranges::lower_bound(data.begin(), data.end(), 4); | ||
auto upper = ranges::upper_bound(data.begin(), data.end(), 4); | auto upper = ranges::upper_bound(data.begin(), data.end(), 4); | ||
| − | + | ||
ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " ")); | ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " ")); | ||
std::cout << '\n'; | std::cout << '\n'; | ||
| Line 113: | Line 144: | ||
auto lower = ranges::lower_bound(data, 3); | auto lower = ranges::lower_bound(data, 3); | ||
auto upper = ranges::upper_bound(data, 3); | auto upper = ranges::upper_bound(data, 3); | ||
| − | + | ||
ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " ")); | ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " ")); | ||
std::cout << '\n'; | std::cout << '\n'; | ||
} | } | ||
| + | |||
| + | using CD = std::complex<double>; | ||
| + | std::vector<CD> nums{<!---->{1, 0}, {2, 2}, {2, 1}, {3, 0}, {3, 1}<!---->}; | ||
| + | auto cmpz = [](CD x, CD y) { return x.real() < y.real(); }; | ||
| + | #ifdef __cpp_lib_algorithm_default_value_type | ||
| + | auto it = ranges::upper_bound(nums, {2, 0}, cmpz); | ||
| + | #else | ||
| + | auto it = ranges::upper_bound(nums, CD{2, 0}, cmpz); | ||
| + | #endif | ||
| + | assert((*it == CD{3, 0})); | ||
} | } | ||
| − | + | |output= | |
4 4 4 | 4 4 4 | ||
3 3 3 3 | 3 3 3 3 | ||
| Line 125: | Line 166: | ||
===See also=== | ===See also=== | ||
{{dsc begin}} | {{dsc begin}} | ||
| − | {{dsc inc | cpp/algorithm/ranges/dsc equal_range}} | + | {{dsc inc|cpp/algorithm/ranges/dsc equal_range}} |
| − | {{dsc inc | cpp/algorithm/ranges/dsc lower_bound}} | + | {{dsc inc|cpp/algorithm/ranges/dsc lower_bound}} |
| − | {{dsc inc | cpp/algorithm/ranges/dsc partition}} | + | {{dsc inc|cpp/algorithm/ranges/dsc partition}} |
| + | {{dsc inc|cpp/algorithm/dsc upper_bound}} | ||
{{dsc end}} | {{dsc end}} | ||
| + | |||
| + | {{langlinks|es|ja|zh}} | ||
Latest revision as of 21:34, 20 May 2024
| Defined in header <algorithm>
|
||
| Call signature |
||
| (1) | ||
template< std::forward_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity, |
(since C++20) (until C++26) |
|
| template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, |
(since C++26) | |
| (2) | ||
| template< ranges::forward_range R, class T, class Proj = std::identity, |
(since C++20) (until C++26) |
|
| template< ranges::forward_range R, class Proj = std::identity, |
(since C++26) | |
1) Returns an iterator pointing to the first element in the range
[first, last) that is greater than value, or last if no such element is found.
The range [first, last) must be partitioned with respect to the expression or !comp(value, element), i.e., all elements for which the expression is true must precede all elements for which the expression is false. A fully-sorted range meets this criterion.2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first and ranges::end(r) as last.
The function-like entities described on this page are niebloids, that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
In practice, they may be implemented as function objects, or with special compiler extensions.
Contents |
[edit] Parameters
| first, last | - | iterator-sentinel defining the partially-ordered range to examine |
| r | - | the partially-ordered range to examine |
| value | - | value to compare the elements to |
| pred | - | predicate to apply to the projected elements |
| proj | - | projection to apply to the elements |
[edit] Return value
Iterator pointing to the first element that is greater than value, or last if no such element is found.
[edit] Complexity
The number of comparisons and applications of the projection performed are logarithmic in the distance between first and last (at most log2(last - first) + O(1) comparisons and applications of the projection). However, for an iterator that does not model random_access_iterator, the number of iterator increments is linear.
[edit] Possible implementation
struct upper_bound_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, class T = std::projected_value_t<I, Proj>, std::indirect_strict_weak_order <const T*, std::projected<I, Proj>> Comp = ranges::less> constexpr I operator()(I first, S last, const T& value, Comp comp = {}, Proj proj = {}) const { I it; std::iter_difference_t<I> count, step; count = ranges::distance(first, last); while (count > 0) { it = first; step = count / 2; ranges::advance(it, step, last); if (!comp(value, std::invoke(proj, *it))) { first = ++it; count -= step + 1; } else count = step; } return first; } template<ranges::forward_range R, class Proj = std::identity, class T = std::projected_value_t<ranges::iterator_t<R>, Proj>, std::indirect_strict_weak_order <const T*, std::projected<ranges::iterator_t<R>, Proj>> Comp = ranges::less> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, const T& value, Comp comp = {}, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), value, std::ref(comp), std::ref(proj)); } }; inline constexpr upper_bound_fn upper_bound; |
[edit] Notes
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_algorithm_default_value_type |
202403 | (C++26) | List-initialization for algorithms (1,2) |
[edit] Example
Run this code
#include <algorithm> #include <cassert> #include <complex> #include <iostream> #include <iterator> #include <vector> int main() { namespace ranges = std::ranges; std::vector<int> data{1, 1, 2, 3, 3, 3, 3, 4, 4, 4, 5, 5, 6}; { auto lower = ranges::lower_bound(data.begin(), data.end(), 4); auto upper = ranges::upper_bound(data.begin(), data.end(), 4); ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " ")); std::cout << '\n'; } { auto lower = ranges::lower_bound(data, 3); auto upper = ranges::upper_bound(data, 3); ranges::copy(lower, upper, std::ostream_iterator<int>(std::cout, " ")); std::cout << '\n'; } using CD = std::complex<double>; std::vector<CD> nums{{1, 0}, {2, 2}, {2, 1}, {3, 0}, {3, 1}}; auto cmpz = [](CD x, CD y) { return x.real() < y.real(); }; #ifdef __cpp_lib_algorithm_default_value_type auto it = ranges::upper_bound(nums, {2, 0}, cmpz); #else auto it = ranges::upper_bound(nums, CD{2, 0}, cmpz); #endif assert((*it == CD{3, 0})); }
Output:
4 4 4 3 3 3 3
[edit] See also
| (C++20) |
returns range of elements matching a specific key (niebloid) |
| (C++20) |
returns an iterator to the first element not less than the given value (niebloid) |
| (C++20) |
divides a range of elements into two groups (niebloid) |
| returns an iterator to the first element greater than a certain value (function template) |
