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/*
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Задача:
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В данном примере написана функция getMax, которая находит максимум из чисел в векторе.
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При этом вычисления проходят однопоточно.
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Вам нужно написать функцию
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uint64_t getMaxPar(int n, const std::vector<uint64_t>& v)
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которая будет делать то же самое, но только использовать для этого n потоков.
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*/
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#include <iostream>
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#include <thread>
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#include <chrono>
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#include <vector>
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#include <random>
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#include <algorithm>
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#include <cstdint>
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#include <functional>
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using std::cout, std::endl, std::size_t;
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using namespace std::chrono_literals;
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uint64_t getMax(std::vector<uint64_t>::const_iterator first, std::vector<uint64_t>::const_iterator last)
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{
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uint64_t res = *first;
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for (; first != last; first++)
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if (*first > res)
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res = *first;
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return res;
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}
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uint64_t getMax(const std::vector<uint64_t>& v) {
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return getMax(v.begin(), v.end());
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}
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struct maxBlock {
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void operator() (std::vector<uint64_t>::const_iterator first, std::vector<uint64_t>::const_iterator last, uint64_t& res) {
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res = getMax(first, last);
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}
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};
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uint64_t getMax(int n, const std::vector<uint64_t>& v) {
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std::vector<uint64_t> results(n);
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std::vector<std::thread> threads(n - 1);
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unsigned long const block_size = v.size() / n;
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auto block_start = v.begin();
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for (int i = 0; i < n - 1; ++i) {
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auto block_end = block_start;
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std::advance(block_end, block_size);
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threads[i] = std::thread(maxBlock(),
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block_start, block_end, std::ref(results[i]));
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block_start = block_end;
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}
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maxBlock() (block_start, v.end(), results[n - 1]);
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std::for_each(threads.begin(), threads.end(), std::mem_fn(&std::thread::join));
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return getMax(results);
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}
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int main()
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{
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cout << "Generating numbers!" << endl;
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std::vector<uint64_t> numbers(5e8);
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numbers[0] = 123456789;
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for (size_t i = 1; i < numbers.size(); ++i)
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{
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numbers[i] = numbers[i - 1] * i + 1;
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}
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cout << "Numbers generated!" << endl;
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auto start = std::chrono::high_resolution_clock::now();
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uint64_t m = getMax(numbers);
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auto end = std::chrono::high_resolution_clock::now();
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cout << "Maximum = " << m << endl;
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cout << "Time to calclulate max = " << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()
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<< " milliseconds." << endl;
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/* Parallel */
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start = std::chrono::high_resolution_clock::now();
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m = getMax(4, numbers);
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end = std::chrono::high_resolution_clock::now();
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cout << "Maximum = " << m << endl;
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cout << "Time to calclulate max = " << std::chrono::duration_cast<std::chrono::milliseconds>(end - start).count()
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<< " milliseconds." << endl;
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}
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