Exercise 3, Sheet 1

mainEx3.cpp

@@ -0,0 +1,52 @@
+#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;
+}
+