example/comprehensions.cpp - master - auroraos/mirror_range-v3

example/comprehensions.cpp
124 строки3 KB
Eric Niebler
snake_case all the concepts to conform with C++20 (#1260)
16 авг 2019, 17:15
16 авг 2019, 17:155b49299
// Range v3 library
//
//  Copyright Eric Niebler 2013-present
//
//  Use, modification and distribution is subject to the
//  Boost Software License, Version 1.0. (See accompanying
//  file LICENSE_1_0.txt or copy at
//  http://www.boost.org/LICENSE_1_0.txt)
//
// Project home: https://github.com/ericniebler/range-v3
//

#include <chrono>
#include <iostream>
#include <range/v3/all.hpp>

using namespace ranges;

int
main()
{
    // Define an infinite range containing all the Pythagorean triples:
    auto triples = views::for_each(views::iota(1), [](int z) {
        return views::for_each(views::iota(1, z + 1), [=](int x) {
            return views::for_each(views::iota(x, z + 1), [=](int y) {
                return yield_if(x * x + y * y == z * z,
                                std::make_tuple(x, y, z));
            });
        });
    });

    //// This alternate syntax also works:
    // auto triples = iota(1)      >>= [] (int z) { return
    //                iota(1, z+1) >>= [=](int x) { return
    //                iota(x, z+1) >>= [=](int y) { return
    //    yield_if(x*x + y*y == z*z,
    //        std::make_tuple(x, y, z)); };}; };

    // Display the first 100 triples
    RANGES_FOR(auto triple, triples | views::take(100))
    {
        std::cout << '(' << std::get<0>(triple) << ',' << std::get<1>(triple)
                  << ',' << std::get<2>(triple) << ')' << '\n';
    }
}

////////////////////////////////////////////////////////////////////////////////////////////////////
//  Benchmark Code
////////////////////////////////////////////////////////////////////////////////////////////////////

class timer
{
private:
    std::chrono::high_resolution_clock::time_point start_;

public:
    timer()
    {
        reset();
    }
    void reset()
    {
        start_ = std::chrono::high_resolution_clock::now();
    }
    std::chrono::milliseconds elapsed() const
    {
        return std::chrono::duration_cast<std::chrono::milliseconds>(
            std::chrono::high_resolution_clock::now() - start_);
    }
    friend std::ostream &operator<<(std::ostream &sout, timer const &t)
    {
        return sout << t.elapsed().count() << "ms";
    }
};

void
benchmark()
{
    // Define an infinite range containing all the Pythagorean triples:
    auto triples = views::for_each(views::iota(1), [](int z) {
        return views::for_each(views::iota(1, z + 1), [=](int x) {
            return views::for_each(views::iota(x, z + 1), [=](int y) {
                return yield_if(x * x + y * y == z * z,
                                std::make_tuple(x, y, z));
            });
        });
    });

    static constexpr int max_triples = 3000;

    timer t;
    int result = 0;
    RANGES_FOR(auto triple, triples | views::take(max_triples))
    {
        int i, j, k;
        std::tie(i, j, k) = triple;
        result += (i + j + k);
    }
    std::cout << t << '\n';
    std::cout << result << '\n';

    result = 0;
    int found = 0;
    t.reset();
    for(int z = 1;; ++z)
    {
        for(int x = 1; x <= z; ++x)
        {
            for(int y = x; y <= z; ++y)
            {
                if(x * x + y * y == z * z)
                {
                    result += (x + y + z);
                    ++found;
                    if(found == max_triples)
                        goto done;
                }
            }
        }
    }
done:
    std::cout << t << '\n';
    std::cout << result << '\n';
}