std::ranges::partial_sort_copy, std::ranges::partial_sort_copy_result
| 在头文件 <algorithm> 中定义 |
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| 调用签名 |
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| template< std::input_iterator I1, std::sentinel_for<I1> S1, std::random_access_iterator I2, std::sentinel_for<I2> S2, |
(1) | (自 C++20) |
| template< ranges::input_range R1, ranges::random_access_range R2, class Comp = ranges::less, class Proj1 = std::identity, |
(2) | (自 C++20) |
| 辅助类型 |
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| template< class I, class O > using partial_sort_copy_result = ranges::in_out_result<I, O>; |
(3) | (自 C++20) |
将源范围 [first, last) 中的前 N 个元素复制到目标范围 [result_first, result_first + N) 中，就好像它是根据 comp 和 proj1 部分排序的，其中 N = min(L₁, L₂)，L₁ 等于 ranges::distance(first, last)，L₂ 等于 ranges::distance(result_first, result_last)。
不保证相等元素的顺序。
本页描述的类函数实体是 niebloids，即
在实践中，它们可能被实现为函数对象，或者使用特殊的编译器扩展。
内容 |
[edit] 参数
| first, last | - | 定义要从中复制的源范围的迭代器-哨兵 |
| r | - | 要从中复制的源范围 |
| result_first, result_last | - | 定义目标范围的迭代器-哨兵 |
| result_r | - | 目标范围 |
| comp | - | 要应用于投影元素的比较 |
| proj1 | - | 要应用于源范围元素的投影 |
| proj2 | - | 要应用于目标范围元素的投影 |
[edit] 返回值
一个与 {last, result_first + N} 相等的 对象。
[edit] 复杂度
最多 L₁•log(N) 次比较和 2•L₁•log(N) 次投影。
[edit] 可能的实现
struct partial_sort_copy_fn { template<std::input_iterator I1, std::sentinel_for<I1> S1, std::random_access_iterator I2, std::sentinel_for<I2> S2, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity> requires std::indirectly_copyable<I1, I2> && std::sortable<I2, Comp, Proj2> && std::indirect_strict_weak_order<Comp, std::projected<I1, Proj1>, std::projected<I2, Proj2>> constexpr ranges::partial_sort_copy_result<I1, I2> operator()(I1 first, S1 last, I2 result_first, S2 result_last, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const { if (result_first == result_last) return {std::move(ranges::next(std::move(first), std::move(last))), std::move(result_first)}; auto out_last{result_first}; // copy first N elements for (; !(first == last or out_last == result_last); ++out_last, ++first) *out_last = *first; // convert N copied elements into a max-heap ranges::make_heap(result_first, out_last, comp, proj2); // process the rest of the input range (if any), preserving the heap property for (; first != last; ++first) { if (std::invoke(comp, std::invoke(proj1, *first), std::invoke(proj2, *result_first))) { // pop out the biggest item and push in a newly found smaller one ranges::pop_heap(result_first, out_last, comp, proj2); *(out_last - 1) = *first; ranges::push_heap(result_first, out_last, comp, proj2); } } // first N elements in the output range is still // a heap - convert it into a sorted range ranges::sort_heap(result_first, out_last, comp, proj2); return {std::move(first), std::move(out_last)}; } template<ranges::input_range R1, ranges::random_access_range R2, class Comp = ranges::less, class Proj1 = std::identity, class Proj2 = std::identity> requires std::indirectly_copyable<ranges::iterator_t<R1>, ranges::iterator_t<R2>> && std::sortable<ranges::iterator_t<R2>, Comp, Proj2> && std::indirect_strict_weak_order<Comp, std::projected<ranges::iterator_t<R1>, Proj1>, std::projected<ranges::iterator_t<R2>, Proj2>> constexpr ranges::partial_sort_copy_result<ranges::borrowed_iterator_t<R1>, ranges::borrowed_iterator_t<R2>> operator()(R1&& r, R2&& result_r, Comp comp = {}, Proj1 proj1 = {}, Proj2 proj2 = {}) const { return (*this)(ranges::begin(r), ranges::end(r), ranges::begin(result_r), ranges::end(result_r), std::move(comp), std::move(proj1), std::move(proj2)); } }; inline constexpr partial_sort_copy_fn partial_sort_copy {}; |
[edit] 示例
#include <algorithm> #include <forward_list> #include <functional> #include <iostream> #include <ranges> #include <string_view> #include <vector> void print(std::string_view rem, std::ranges::input_range auto const& v) { for (std::cout << rem; const auto& e : v) std::cout << e << ' '; std::cout << '\n'; } int main() { const std::forward_list source{4, 2, 5, 1, 3}; print("Write to the smaller vector in ascending order: ", ""); std::vector dest1{10, 11, 12}; print("const source list: ", source); print("destination range: ", dest1); std::ranges::partial_sort_copy(source, dest1); print("partial_sort_copy: ", dest1); print("Write to the larger vector in descending order:", ""); std::vector dest2{10, 11, 12, 13, 14, 15, 16}; print("const source list: ", source); print("destination range: ", dest2); std::ranges::partial_sort_copy(source, dest2, std::greater{}); print("partial_sort_copy: ", dest2); }
输出
Write to the smaller vector in ascending order: const source list: 4 2 5 1 3 destination range: 10 11 12 partial_sort_copy: 1 2 3 Write to the larger vector in descending order: const source list: 4 2 5 1 3 destination range: 10 11 12 13 14 15 16 partial_sort_copy: 5 4 3 2 1 15 16
[edit] 参见
| (C++20) |
对范围的前 N 个元素进行排序 (niebloid) |
| (C++20) |
将范围排序为升序 (niebloid) |
| (C++20) |
对元素范围进行排序，同时保留相等元素之间的顺序 (niebloid) |
| (C++20) |
将最大堆转换为按升序排序的元素范围 (niebloid) |
| (C++20) |
从元素范围创建最大堆 (niebloid) |
| (C++20) |
将元素添加到最大堆 (niebloid) |
| (C++20) |
从最大堆中删除最大元素 (niebloid) |
| 复制并部分排序元素范围 (函数模板) |
