Initial data commit

Task/Factorial/C-sharp/factorial-1.cs

@@ -0,0 +1,22 @@
+using System;
+
+class Program
+{
+    static int Factorial(int number)
+    {
+        if(number < 0)
+            throw new ArgumentOutOfRangeException(nameof(number), number, "Must be zero or a positive number.");
+
+        var accumulator = 1;
+        for (var factor = 1; factor <= number; factor++)
+        {
+            accumulator *= factor;
+        }
+        return accumulator;
+    }
+
+    static void Main()
+    {
+        Console.WriteLine(Factorial(10));
+    }
+}

Task/Factorial/C-sharp/factorial-2.cs

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+using System;
+
+class Program
+{
+    static int Factorial(int number)
+    {
+        if(number < 0)
+            throw new ArgumentOutOfRangeException(nameof(number), number, "Must be zero or a positive number.");
+
+        return number == 0 ? 1 : number * Factorial(number - 1);
+    }
+
+    static void Main()
+    {
+        Console.WriteLine(Factorial(10));
+    }
+}

Task/Factorial/C-sharp/factorial-3.cs

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+using System;
+
+class Program
+{
+    static int Factorial(int number)
+    {
+        if(number < 0)
+            throw new ArgumentOutOfRangeException(nameof(number), number, "Must be zero or a positive number.");
+
+        return Factorial(number, 1);
+    }
+
+    static int Factorial(int number, int accumulator)
+    {
+        if(number < 0)
+            throw new ArgumentOutOfRangeException(nameof(number), number, "Must be zero or a positive number.");
+        if(accumulator < 1)
+            throw new ArgumentOutOfRangeException(nameof(accumulator), accumulator, "Must be a positive number.");
+
+        return number == 0 ? accumulator : Factorial(number - 1, number * accumulator);
+    }
+
+    static void Main()
+    {
+        Console.WriteLine(Factorial(10));
+    }
+}

Task/Factorial/C-sharp/factorial-4.cs

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+using System;
+using System.Linq;
+
+class Program
+{
+    static int Factorial(int number)
+    {
+        return Enumerable.Range(1, number).Aggregate((accumulator, factor) => accumulator * factor);
+    }
+
+    static void Main()
+    {
+        Console.WriteLine(Factorial(10));
+    }
+}

Task/Factorial/C-sharp/factorial-5.cs

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+using System;
+using System.Numerics;
+using System.Linq;
+class Program
+{
+    static BigInteger factorial(int n) // iterative
+    {
+        BigInteger acc = 1; for (int i = 1; i <= n; i++) acc *= i; return acc;
+    }
+
+    static public BigInteger Factorial(int number) // functional
+    {
+        return Enumerable.Range(1, number).Aggregate(new BigInteger(1), (acc, num) => acc * num);
+    }
+
+    static public BI FactorialQ(int number) // functional quick, uses prodtree method
+    {
+        var s = Enumerable.Range(1, number).Select(num => new BI(num)).ToArray();
+        int top = s.Length, nt, i, j;
+        while (top > 1) {
+            for (i = 0, j = top, nt = top >> 1; i < nt; i++) s[i] *= s[--j];
+            top = nt + ((top & 1) == 1 ? 1 : 0);
+        }
+        return s[0];
+    }
+
+    static void Main(string[] args)
+    {
+        Console.WriteLine(Factorial(250));
+    }
+}