std::ranges::adjacent_find
来自 cppreference.com
| 定义在头文件中 <algorithm> |
||
| 调用签名 |
||
| template< std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_binary_predicate< |
(1) | (自 C++20 起) |
| template< ranges::forward_range R, class Proj = std::identity, std::indirect_binary_predicate< |
(2) | (自 C++20 起) |
在范围内搜索 [first, last) 查找前两个连续相等的元素。
1) 使用 pred 比较元素（在使用投影 proj 投影后）。
此页面上描述的功能状实体是 niebloids，即
在实践中，它们可以实现为函数对象，或使用特殊的编译器扩展。
内容 |
[编辑] 参数
| first, last | - | 要检查的元素范围 |
| r | - | 要检查的元素范围 |
| pred | - | 应用于投影元素的谓词 |
| proj | - | 应用于元素的投影 |
[编辑] 返回值
指向第一个相同元素对的第一个元素的迭代器，即第一个迭代器 it 使得 bool(std::invoke(pred, std::invoke(proj1, *it), std::invoke(proj, *(it + 1)))) 为 true.
如果未找到此类元素，则返回等于 last 的迭代器。
[编辑] 复杂度
正好 min((result - first) + 1, (last - first) - 1) 次谓词和投影的应用，其中 result 是返回值。
[编辑] 可能的实现
struct adjacent_find_fn { template<std::forward_iterator I, std::sentinel_for<I> S, class Proj = std::identity, std::indirect_binary_predicate< std::projected<I, Proj>, std::projected<I, Proj>> Pred = ranges::equal_to> constexpr I operator()(I first, S last, Pred pred = {}, Proj proj = {}) const { if (first == last) return first; auto next = ranges::next(first); for (; next != last; ++next, ++first) if (std::invoke(pred, std::invoke(proj, *first), std::invoke(proj, *next))) return first; return next; } template<ranges::forward_range R, class Proj = std::identity, std::indirect_binary_predicate< std::projected<ranges::iterator_t<R>, Proj>, std::projected<ranges::iterator_t<R>, Proj>> Pred = ranges::equal_to> constexpr ranges::borrowed_iterator_t<R> operator()(R&& r, Pred pred = {}, Proj proj = {}) const { return (*this)(ranges::begin(r), ranges::end(r), std::ref(pred), std::ref(proj)); } }; inline constexpr adjacent_find_fn adjacent_find; |
[编辑] 示例
运行此代码
#include <algorithm> #include <functional> #include <iostream> #include <ranges> constexpr bool some_of(auto&& r, auto&& pred) // some but not all { return std::ranges::cend(r) != std::ranges::adjacent_find(r, [&pred](auto const& x, auto const& y) { return pred(x) != pred(y); }); } // test some_of constexpr auto a = {0, 0, 0, 0}, b = {1, 1, 1, 0}, c = {1, 1, 1, 1}; auto is_one = [](auto x){ return x == 1; }; static_assert(!some_of(a, is_one) && some_of(b, is_one) && !some_of(c, is_one)); int main() { const auto v = {0, 1, 2, 3, 40, 40, 41, 41, 5}; /* ^^ ^^ */ namespace ranges = std::ranges; if (auto it = ranges::adjacent_find(v.begin(), v.end()); it == v.end()) std::cout << "No matching adjacent elements\n"; else std::cout << "The first adjacent pair of equal elements is at [" << ranges::distance(v.begin(), it) << "] == " << *it << '\n'; if (auto it = ranges::adjacent_find(v, ranges::greater()); it == v.end()) std::cout << "The entire vector is sorted in ascending order\n"; else std::cout << "The last element in the non-decreasing subsequence is at [" << ranges::distance(v.begin(), it) << "] == " << *it << '\n'; }
输出
The first adjacent pair of equal elements is at [4] == 40 The last element in the non-decreasing subsequence is at [7] == 41
[编辑] 参见
| (C++20) |
移除范围内的连续重复元素 (niebloid) |
| 找到第一个两个相邻的相等项（或满足给定谓词的项） (函数模板) |
