chore(CSharp): Added Sieve of Eratosthenes to generate primes from 1 to N (#502)

algorithms/CSharp/README.md

@@ -6,6 +6,7 @@ For running the `.cs` file please using [.Net Finddle](https://dotnetfiddle.net/
 
 ## Number Theory
 1. [Big Mod Algorithm](src/Number-Theory/big-mod.cs)
+2. [Sieve of Eratosthenes](src/Number-Theory/sieve-of-eratosthenes.cs)
 
 ## Sorts
 

algorithms/CSharp/src/Number-Theory/sieve-of-eratosthenes.cs

@@ -0,0 +1,46 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+
+namespace Algorithms.NumberTheory
+{
+    public class SieveOfEratosthenes
+    {
+        // returns all the prime numbers from 1 to max
+        public static List<int> PrimeGenerator(int max)
+        {
+            List<bool> isPrime = Enumerable.Repeat(true, max + 1).ToList();
+
+            isPrime[0] = isPrime[1] = false;
+            for(int i = 4; i <= max; i += 2)
+            {
+                isPrime[i] = false;
+            }
+
+            int squareRoot = (int)Math.Sqrt(max);
+            for(int i = 3; i <= squareRoot; i += 2)
+            {
+                if(isPrime[i])
+                {
+                    for(int j = 2 * i; j <= max; j += i)
+                    {
+                        isPrime[j] = false;
+                    }
+                }
+            }
+
+            List<int> primeNumbers = isPrime.Select((value, index) => new { value, index })
+                                            .Where(obj => obj.value == true)
+                                            .Select(obj => obj.index)
+                                            .ToList();
+
+            return primeNumbers;
+        }
+
+        public static void Main()
+        {
+            List<int> primeNumbers = PrimeGenerator(100);
+            Console.WriteLine(string.Join(", ", primeNumbers));
+        }
+    }
+}

algorithms/CSharp/test/Number-Theory/sieve-of-eratosthenes.cs

@@ -0,0 +1,16 @@
+using NUnit.Framework;
+using System.Collections.Generic;
+
+namespace Algorithms.Tests.NumberTheory
+{
+    [TestFixture]
+    public class SieveOfEratosthenes
+    {
+        [TestCase(100, "2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53, 59, 61, 67, 71, 73, 79, 83, 89, 97")]
+        public void SieveOfEratosthenes_ShouldReturnExpected(int max, string expected)
+        {
+            List<int> primeNumbers = Algorithms.NumberTheory.SieveOfEratosthenes.PrimeGenerator(max);
+            Assert.AreEqual(expected, string.Join(", ", primeNumbers));
+        }
+    }
+}