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