cleverboysum.cpp

#include <cstdint>
#include <chrono>
#include <iostream>

using namespace std;

int64_t naive_sum(int64_t x) {
    int64_t sum = 0;
    for(int64_t i = 0; i < x; i++) {
        sum += i;
    }
    return sum;
}

int64_t clever_boy_sum(int64_t x) {
	return x * (x + 1) / 2;
}


int main() {
	int64_t xor_result = 7;
	auto start =chrono::system_clock::now();
	for(int i = 0; i < 100000000; i++) {
		xor_result ^= naive_sum(100000000);
	}
	auto end = chrono::system_clock::now();

	auto elapsed =
		std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
	std::cout << "Naive Sum: " << elapsed.count() << "ms (" << xor_result << ")\n";

	xor_result = 7;
	start =chrono::system_clock::now();
	for(int i = 0; i < 100000000; i++) {
		xor_result ^= clever_boy_sum(100000000);
	}
	end = chrono::system_clock::now();

	elapsed =
		std::chrono::duration_cast<std::chrono::milliseconds>(end - start);
	std::cout << "Clever Boy Sum: " << elapsed.count() << "ms (" << xor_result << ")\n";
}