C++ std::partial_sort_copy 用法

一：功能

        部分排序，即选出前n个最大值或者最小值，并将其保存到另外一个容器中。

二：用法

#include <vector>
#include <algorithm>
#include <iostream>
#include <iterator>
 
int main() {
    std::vector<int> top(3);
 
    auto input = std::istream_iterator<int>(std::cin);
    auto cnt = std::counted_iterator(input, 10);
 
    std::ranges::partial_sort_copy(cnt, std::default_sentinel, 
        top.begin(), top.end(), 
        std::greater<>{});
    for (auto v : top) {
        std::cout << v << " ";
    }
    std::cout << "\n";
}

#include <algorithm>
#include <functional>
#include <iostream>
#include <string_view>
#include <type_traits>
#include <vector>
 
void println(std::string_view rem, const auto& v)
{
    std::cout << rem;
    if constexpr (std::is_scalar_v<std::decay_t<decltype(v)>>)
        std::cout << v;
    else
        for (int e : v)
            std::cout << e << ' ';
    std::cout << '\n';
}
 
int main()
{
    const auto v0 = {4, 2, 5, 1, 3};
    std::vector<int> v1{10, 11, 12};
    std::vector<int> v2{10, 11, 12, 13, 14, 15, 16};
    std::vector<int>::iterator it;
 
    it = std::partial_sort_copy(v0.begin(), v0.end(), v1.begin(), v1.end());
    println("Writing to the smaller vector in ascending order gives: ", v1);
 
    if (it == v1.end())
        println("The return value is the end iterator", ' ');
 
    it = std::partial_sort_copy(v0.begin(), v0.end(), v2.begin(), v2.end(),
                                std::greater<int>());
 
    println("Writing to the larger vector in descending order gives: ", v2);
    println("The return value is the iterator to ", *it);
}