two-number-sum.cpp

#include <random>
#include <iostream>
#include <set>
#include <chrono>
#include <iomanip>

constexpr int sum = 70;
constexpr int size = 1000;

void cout(const ulong &u1, const ulong &u2)
{
    (void)u1;
    (void)u2;
}

void test_basic(const std::vector<ulong> &vec) {
    for(auto i = 0; i < size; i++)
        for(auto j = 0; j < size; j++)
            if (vec.at(i) + vec.at(j) == sum)
                cout(vec.at(i), vec.at(j));
}

void test_set(const std::vector<ulong> &vec) {
    std::set<ulong> set;

    for(auto i = 0; i < size; i++) {
        auto p = set.find(sum - vec.at(i));
        if (p != set.end())
            cout(vec.at(i), *p);
        set.emplace(vec.at(i));
    }
}

void run_test()
{
    std::vector<unsigned long> vec;
    std::random_device dev;
    std::mt19937 rng(dev());
    std::uniform_int_distribution<std::mt19937::result_type> dist(1,100);

    for(auto i = 0; i < size; i++)
        vec.push_back(dist(rng));

    auto start_basic = std::chrono::high_resolution_clock::now();
    test_basic(vec);
    auto end_basic = std::chrono::high_resolution_clock::now();

    auto start_set = std::chrono::high_resolution_clock::now();
    test_set(vec);
    auto end_set = std::chrono::high_resolution_clock::now();

    double elapsed_time_basic = std::chrono::duration<double, std::milli>(end_basic - start_basic).count();
    double elapsed_time_set = std::chrono::duration<double, std::milli>(end_set - start_set).count();

    std::cout << std::fixed << std::setprecision(6)
              << "Basic=" << std::showbase<<std::setw(10) << elapsed_time_basic
              << std::setw(6)
              << "Set=" << std::setw(10) << elapsed_time_set << std::endl;
}
int main(int, char *[])
{
    for (auto i = 0; i < 20; i++)
        run_test();

    return EXIT_SUCCESS;
}