Sieve of Eratosthenes (#49)

* Sieve Of Eratosthenes An algorithm to generate all prime numbers up to a certain number * Sieve of Eratosthenes test Tests the Sieve of Eratosthenese implementation * Delete SieveOfEratosthenes.cs * Add files via upload * Delete SieveOfEratosthenesTest.cs * Add files via upload * Added Sieve of Eratosthenes test Added Sieve of Eratosthenes test
aalhour · Nov 19, 2017 · a9d335e · a9d335e
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diff --git a/Algorithms/Numeric/SieveOfEratosthenes.cs b/Algorithms/Numeric/SieveOfEratosthenes.cs
@@ -0,0 +1,57 @@
+using System;
+using System.Collections.Generic;
+
+/***
+* Generates all prime numbers up to a given number
+* Wikipedia: https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+*/
+
+
+namespace Algorithms.Numeric
+{
+    public static class SieveOfEratosthenes
+    {
+        /// <summary>
+        /// Calculate primes up to a given number
+        /// </summary>
+        public static List<int> GeneratePrimesUpTo(int x)
+        {
+
+            //The list of primes that will be returned
+            List<int> primesList = new List<int>();
+
+            //Returns an empty list if x is a value under 2
+            if (x < 2)
+            {
+                return primesList;
+            }
+
+            //Adds every number between 2 and x to the list
+            for (int i = 2; i <= x; i++)
+            {
+                primesList.Add(i);
+            }
+
+            //integer that all multiples of will be removed from the list
+            int removeMultiplesOf;
+
+            //Finds the next number in the list that hasn't been removed and removes all multiples of that number 
+            //from the list
+            for (int i = 2; i <= Math.Sqrt(x); i++)
+            {
+                if (primesList.Contains(i))
+                {
+                    removeMultiplesOf = i;
+                    for (int j = removeMultiplesOf*removeMultiplesOf; j <= x; j += removeMultiplesOf)
+                    {
+                        primesList.Remove(j);
+                    }
+                }
+            }
+
+            //The list of primes is returned
+            return primesList;
+        }
+
+    }
+}
diff --git a/MainProgram/AlgorithmsTests/SieveOfEratosthenesTest.cs b/MainProgram/AlgorithmsTests/SieveOfEratosthenesTest.cs
@@ -0,0 +1,33 @@
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+
+namespace C_Sharp_Algorithms.AlgorithmsTests
+{
+    class SieveOfEratosthenesTest
+    {
+
+        //Test lists
+        static List<int> testList = new List<int>();
+        static List<int> primesUpTo100List = new List<int>{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};
+        static List<int> primesUpTo2List = new List<int> { 2 };
+        static List<int> emptyList = new List<int>();
+
+        public static void DoTest()
+        {
+            //Check if algorithm returns expected lists
+            testList = Algorithms.Numeric.SieveOfEratosthenes.GeneratePrimesUpTo(100);
+            Debug.Assert(testList.SequenceEqual(primesUpTo100List));
+
+            testList = Algorithms.Numeric.SieveOfEratosthenes.GeneratePrimesUpTo(2);
+            Debug.Assert(testList.SequenceEqual(primesUpTo2List));
+
+            testList = Algorithms.Numeric.SieveOfEratosthenes.GeneratePrimesUpTo(1);
+            Debug.Assert(testList.SequenceEqual(emptyList));
+
+            testList = Algorithms.Numeric.SieveOfEratosthenes.GeneratePrimesUpTo(-100);
+            Debug.Assert(testList.SequenceEqual(emptyList));
+
+        }
+    }
+}