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Lisa Pizzo 2025-10-29 18:19:02 +01:00
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mainEx3.cpp
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#include <iostream>
#include <chrono>
using namespace std;
using namespace std::chrono;
long long sumMultiplesLoop(int n) { // long long is like int but for big numbers
long long sum = 0;
for (int i = 1; i <= n; ++i) {
if (i % 3 == 0 || i % 5 == 0) {
sum += i;
}
}
return sum;
}
long long sumOfMultiples(int n, int k) { //known formula: k*m*(m+1)/2 for multiples of k leq n
long long m = n / k; // how many multiples
return (long long)k * m * (m + 1) / 2;
}
// Formula version (no loop)
long long sumMultiplesFormula(int n) {
return sumOfMultiples(n, 3) + sumOfMultiples(n, 5) - sumOfMultiples(n, 15); //subtract multiples of 15 because they count double
}
int main() {
int n = 1432987;
auto start1 = high_resolution_clock::now();
long long result1 = 0;
for (int i = 0; i < 1000; ++i) {
result1 = sumMultiplesLoop(n);
}
auto end1 = high_resolution_clock::now();
duration<double> average1 = (end1 - start1) / 1000;
auto start2 = high_resolution_clock::now();
long long result2 = 0;
for (int i = 0; i < 1000; ++i) {
result2 = sumMultiplesFormula(n);
}
auto end2 = high_resolution_clock::now();
duration<double> average2 = (end2 - start2) / 1000;
cout << "Loop result: " << result1 << endl;
cout << "Loop average time: " << average1.count() << " seconds" << endl;
cout << "Formula result: " << result2 << endl;
cout << "Formula average time: " << average2.count() << " seconds" << endl;
return 0;
}