std::ranges::upper_bound
来自cppreference.com
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| 在标头 <algorithm> 定义
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| 调用签名 |
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| (1) | ||
template< std::forward_iterator I, std::sentinel_for<I> S, class T, class Proj = std::identity, std::indirect_strict_weak_order <const T*, std::projected<I, Proj>> Comp = ranges::less > constexpr I upper_bound( I first, S last, const T& value, Comp comp = {}, Proj proj = {} ); |
(C++20 起) (C++26 前) |
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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 upper_bound( I first, S last, const T& value, Comp comp = {}, Proj proj = {} ); |
(C++26 起) | |
| (2) | ||
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 = {} ); |
(C++20 起) (C++26 前) |
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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 = {} ); |
(C++26 起) | |
1) 返回指向范围
[first, last) 中首个大于 value 的元素的迭代器，或若找不到这种元素返回 last。
范围 [first, last) 必须已按照表达式 !comp(value, element) 划分，即所有该表达式对其为 true 的元素必须前趋所有该表达式对其为 false 的元素。完全排序的范围符合此判别标准。2) 同 (1)，但以
r 为源范围，如同以 ranges::begin(r) 为 first 并以 ranges::end(r) 为 last。此页面上描述的函数式实体是算法函数对象（非正式地称为 niebloid），即：
参数
| first, last | - | 要检验的部分有序元素范围的迭代器-哨位对 |
| r | - | 要检验的部分有序范围 |
| value | - | 要与元素比较的值 |
| pred | - | 应用到投影后元素的谓词 |
| proj | - | 应用到元素的投影 |
返回值
指向首个大于 value 的元素的迭代器，或若找不到这种元素则为 last。
复杂度
比较和应用投影的次数与 first 和 last 之间的距离成对数（至多比较和应用投影 log2(last - first) + O(1) 次）。然而，对于不实现 random_access_iterator 的迭代器，迭代器自增次数为线性。
可能的实现
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;
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注解
| 功能特性测试宏 | 值 | 标准 | 功能特性 |
|---|---|---|---|
__cpp_lib_algorithm_default_value_type |
202403 |
(C++26) | 算法中的列表初始化 (1,2) |
示例
运行此代码
#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}));
}
输出：
4 4 4
3 3 3 3
参阅
(C++20) |
返回匹配特定键值的元素范围 (算法函数对象) |
(C++20) |
返回首个不小于 给定值的元素的迭代器 (算法函数对象) |
(C++20) |
将范围中元素分为两组 (算法函数对象) |
| 返回首个大于 给定值的元素的迭代器 (函数模板) |