From ff2fb3cca4f2d2cc6d9aea3e7493420cb5bbb441 Mon Sep 17 00:00:00 2001
From: "lisa.pizzo" <lisa.pizzo@noreply.imsc.uni-graz.at>
Date: Wed, 22 Oct 2025 16:00:44 +0200
Subject: [PATCH] Exercise 3, Sheet 1

---
 mainEx3.cpp | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 52 insertions(+)
 create mode 100644 mainEx3.cpp

diff --git a/mainEx3.cpp b/mainEx3.cpp
new file mode 100644
index 0000000..94b606b
--- /dev/null
+++ b/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;
+}
+