From 7ce3167f874b6083627e2b98ccfb881565f1b757 Mon Sep 17 00:00:00 2001
From: Waqar Hassan Khan <waqar.hassan866@gmail.com>
Date: Fri, 3 Sep 2021 20:42:30 +0600
Subject: [PATCH] chore(CSharp): added algorithm to determine factorial  (#437)

---
 algorithms/CSharp/README.md                   |  3 +++
 algorithms/CSharp/src/Recursion/factorial.cs  | 27 +++++++++++++++++++
 algorithms/CSharp/test/Recursion/factorial.cs | 18 +++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 algorithms/CSharp/src/Recursion/factorial.cs
 create mode 100644 algorithms/CSharp/test/Recursion/factorial.cs

diff --git a/algorithms/CSharp/README.md b/algorithms/CSharp/README.md
index 9273af3b..5430e572 100644
--- a/algorithms/CSharp/README.md
+++ b/algorithms/CSharp/README.md
@@ -16,3 +16,6 @@ For running the `.cs` file please using [.Net Finddle](https://dotnetfiddle.net/
 
 ## Maths
 - [Abundant Number](src/Maths/abundant-number.cs)
+
+## Recusrsion
+- [Factorial](src/Recursion/factorial.cs)
\ No newline at end of file
diff --git a/algorithms/CSharp/src/Recursion/factorial.cs b/algorithms/CSharp/src/Recursion/factorial.cs
new file mode 100644
index 00000000..c82b5c09
--- /dev/null
+++ b/algorithms/CSharp/src/Recursion/factorial.cs
@@ -0,0 +1,27 @@
+using System;
+
+namespace Algorithms.Recursion
+{
+    public class Factorial
+    {
+        public static int FactorialUsingRecursion(int number)
+        {
+            if(number == 0 || number == 1)
+            {
+                return 1;
+            }
+
+            return number * FactorialUsingRecursion(number - 1);
+        }
+
+        public static void Main()
+        {
+            Console.WriteLine($"Factorial of 7 is: {FactorialUsingRecursion(17)}");
+        }
+    }
+}
+
+/*
+ * n! = n * (n - 1) * (n - 2) * .... * 3 * 2 * 1
+ * we have used int here but for larger number, int will not be enough
+ */
\ No newline at end of file
diff --git a/algorithms/CSharp/test/Recursion/factorial.cs b/algorithms/CSharp/test/Recursion/factorial.cs
new file mode 100644
index 00000000..8c701731
--- /dev/null
+++ b/algorithms/CSharp/test/Recursion/factorial.cs
@@ -0,0 +1,18 @@
+using NUnit.Framework;
+
+namespace Algorithms.Tests.Recursion
+{
+    [TestFixture]
+    public class FactorialTest
+    {
+        [TestCase(0, 1)]
+        [TestCase(7, 5040)]
+        [TestCase(3, 6)]
+        [TestCase(1, 1)]
+        public void TestFactorial_ShouldGetExpectedResult(int number, int expected)
+        {
+            int result = Algorithms.Recursion.Factorial.FactorialUsingRecursion(number);
+            Assert.AreEqual(expected, result);
+        }
+    }
+}