From f99f948fd16af0ef615fcce0c99f95ebf74240b7 Mon Sep 17 00:00:00 2001
From: Gonzalo Diaz <devel@gon.cl>
Date: Wed, 8 May 2024 15:18:56 -0400
Subject: [PATCH] =?UTF-8?q?[Hacker=20Rank]:=20Project=20Euler=20#1:=20Mult?=
 =?UTF-8?q?iples=20of=203=20and=205=20solved=20=E2=9C=93?=
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---
 .../hackerrank/projecteuler/Euler001.Test.cs  | 29 +++++++++++++++
 .../src/hackerrank/projecteuler/Euler001.cs   | 36 +++++++++++++++++++
 2 files changed, 65 insertions(+)
 create mode 100644 algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.Test.cs
 create mode 100644 algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.cs

diff --git a/algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.Test.cs b/algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.Test.cs
new file mode 100644
index 0000000..ab99670
--- /dev/null
+++ b/algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.Test.cs
@@ -0,0 +1,29 @@
+namespace algorithm_exercises_csharp.hackerrank.prohecteuler;
+
+[TestClass]
+public class Euler001Test
+{
+  public class Euler001TestCase {
+    public int a; public int b; public int n; public int answer;
+  }
+
+  // dotnet_style_readonly_field = true
+  private static readonly Euler001TestCase[] tests = [
+    new() { a = 3, b = 5, n = 10, answer = 23},
+    new() { a = 3, b = 5, n = 100, answer = 2318},
+    new() { a = 3, b = 5, n = 1000, answer = 233168},
+
+  ];
+
+  [TestMethod]
+  public void Euler001ProblemTest()
+  {
+    int result;
+
+    foreach (Euler001TestCase test in tests) {
+      result = Euler001Problem.Euler001(test.a, test.b, test.n);
+        Assert.AreEqual(test.answer, result);
+    }
+  }
+}
+
diff --git a/algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.cs b/algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.cs
new file mode 100644
index 0000000..553a822
--- /dev/null
+++ b/algorithm-exercises-csharp/src/hackerrank/projecteuler/Euler001.cs
@@ -0,0 +1,36 @@
+namespace algorithm_exercises_csharp.hackerrank.prohecteuler;
+
+using System.Diagnostics.CodeAnalysis;
+
+public class Euler001Problem
+{
+  [ExcludeFromCodeCoverage]
+  protected Euler001Problem() {}
+
+  public static int SuOfArithmeticProgression(int n, int d) {
+    int new_n = n / d;
+
+    return new_n * (1 + new_n) * d / 2;
+  }
+
+  public static int GCD(int u, int v)
+  {
+    if (v != 0)
+    {
+        return GCD(v, u % v);
+    }
+    return u;
+  }
+
+  // Function to find the sum of all multiples of a and b below n
+  public static int Euler001(int a, int b, int n)
+  {
+    // Since, we need the sum of multiples less than N
+    int new_n = n - 1;
+    int lcm = a * b / GCD(a, b);
+
+    return SuOfArithmeticProgression(new_n, a) +
+      SuOfArithmeticProgression(new_n, b) -
+      SuOfArithmeticProgression(new_n, lcm);
+  }
+}