std::ranges::partial_sort_copy, std::ranges::partial_sort_copy_result
定义于头文件 <algorithm>
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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) | (C++20 起) |
template< ranges::input_range R1, ranges::random_access_range R2, class Comp = ranges::less, class Proj1 = std::identity, |
(2) | (C++20 起) |
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) | (C++20 起) |
复制来自源范围 [first, last)
的首 N
个元素,如同它按照 comp
与 proj1
部分排序,到目标范围 [result_first, result_first + N)
,其中 N = min(L₁, L₂) , L₁ 等于 ranges::distance(first, last) 而 L₂ 等于 ranges::distance(result_first, result_last) 。
不保证保持相等元素的顺序。
proj1
投影源范围元素,并用函数对象 proj2
投影目标元素。r
为源范围并以 result_r
为目标范围,如同以 ranges::begin(r) 为 first
,以 ranges::end(r) 为 last
,以 ranges::begin(result_r) 为 result_first
,并以 ranges::end(result_r) 为 result_last
。此页面上描述的仿函数实体是 niebloid ,即:
实际上,它们能以函数对象,或以某些特殊编译器扩展实现。
参数
first, last | - | 定义复制来源的源范围的迭代器-哨位对 |
r | - | 复制来源的源范围 |
result_first, result_last | - | 定义目标范围的迭代器-哨位对 |
result_r | - | 目标范围 |
comp | - | 应用到投影后元素的比较 |
proj1 | - | 应用到源范围元素的投影 |
proj2 | - | 应用到目标范围元素的投影 |
返回值
等于 {last, result_first + N} 的对象。
复杂度
至多比较 L₁•log(N) 次,投影 2•L₁•log(N) 次。
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}; // 复制首 N 个元素 for (; !(first == last or out_last == result_last); ++out_last, ++first) { *out_last = *first; } // 转换 N 个复制的元素为最大堆 ranges::make_heap(result_first, out_last, comp, proj2); // 处理剩余的输入范围(若存在),保持堆属性 for (; first != last; ++first) { if (std::invoke(comp, std::invoke(proj1, *first), std::invoke(proj2, *result_first))) { // 弹出最大项并塞入新找到的较小项 ranges::pop_heap(result_first, out_last, comp, proj2); *(out_last - 1) = *first; ranges::push_heap(result_first, out_last, comp, proj2); } } // 输出范围中首 N 个元素仍为堆——转换之为已排序范围 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{}; |
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
参阅
(C++20) |
排序一个范围的前 N 个元素 (niebloid) |
(C++20) |
将范围按升序排序 (niebloid) |
(C++20) |
将范围内的元素排序,同时保持相等的元素之间的顺序 (niebloid) |
(C++20) |
将一个最大堆变成一个按升序排序的元素范围 (niebloid) |
(C++20) |
从一个元素范围创建出一个最大堆 (niebloid) |
(C++20) |
将一个元素加入到一个最大堆 (niebloid) |
(C++20) |
从最大堆中移除最大元素 (niebloid) |
对范围内的元素进行复制并部分排序 (函数模板) |