From 16be0f2763d38135c77dc044aa69173e9b3c894a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Micha=C5=82=20=C5=BBarnecki?= <michalzarnecki88@gmail.com>
Date: Mon, 19 Aug 2024 06:32:25 +0200
Subject: [PATCH] Sieve of Eratosthenes algorithm (#159)

Co-authored-by: Michal Zarnecki <michal.zarnecki@companyhouse.de>
---
 DIRECTORY.md                          |  2 ++
 Maths/EratosthenesSieve.php           | 30 +++++++++++++++++++++++++++
 tests/Maths/EratosthenesSieveTest.php | 16 ++++++++++++++
 3 files changed, 48 insertions(+)
 create mode 100644 Maths/EratosthenesSieve.php
 create mode 100644 tests/Maths/EratosthenesSieveTest.php

diff --git a/DIRECTORY.md b/DIRECTORY.md
index 784ee99f..95a62b4c 100644
--- a/DIRECTORY.md
+++ b/DIRECTORY.md
@@ -57,6 +57,7 @@
     * [Problem7](./Maths/ProjectEuler/Problem7.php)
     * [Problem8](./Maths/ProjectEuler/Problem8.php)
     * [Problem9](./Maths/ProjectEuler/Problem9.php)
+  * [Eratosthenessieve](./Maths/EratosthenesSieve.php)
 
 ## Searches
   * [Binarysearch](./Searches/BinarySearch.php)
@@ -119,6 +120,7 @@
   * Maths
     * [Mathstest](./tests/Maths/MathsTest.php)
     * [Projecteulertest](./tests/Maths/ProjectEulerTest.php)
+    * [Eratosthenessievetest](./tests/Maths/EratosthenesSieveTest.php)
   * Searches
     * [Searchestest](./tests/Searches/SearchesTest.php)
   * Sorting
diff --git a/Maths/EratosthenesSieve.php b/Maths/EratosthenesSieve.php
new file mode 100644
index 00000000..d0380d09
--- /dev/null
+++ b/Maths/EratosthenesSieve.php
@@ -0,0 +1,30 @@
+<?php
+
+/**
+ * The Sieve of Eratosthenes is an algorithm is an ancient algorithm for finding all prime numbers up to any given limit
+ * https://en.wikipedia.org/wiki/Sieve_of_Eratosthenes
+ *
+ * @author Michał Żarnecki https://github.com/rzarno
+ * @param int $number the limit of prime numbers to generate
+ * @return string[] prime numbers up to the given limit
+ */
+function eratosthenesSieve(int $number): array
+{
+    $primes = range(1, $number);
+    $primes = array_combine($primes, $primes);
+    $limit = sqrt($number);
+    $current = 2;
+    while ($current < $limit) {
+        $multiplied = $current;
+        $factor = 1;
+        while ($multiplied < $number) {
+            $factor++;
+            $multiplied = $current * $factor;
+            if (isset($primes[$multiplied])) {
+                unset($primes[$multiplied]);
+            }
+        }
+        $current += 1;
+    }
+    return array_values($primes);
+}
diff --git a/tests/Maths/EratosthenesSieveTest.php b/tests/Maths/EratosthenesSieveTest.php
new file mode 100644
index 00000000..065ab638
--- /dev/null
+++ b/tests/Maths/EratosthenesSieveTest.php
@@ -0,0 +1,16 @@
+<?php
+
+require_once __DIR__ . '/../../vendor/autoload.php';
+require_once __DIR__ . '/../../Maths/EratosthenesSieve.php';
+
+use PHPUnit\Framework\TestCase;
+
+class EratosthenesSieveTest extends TestCase
+{
+    public function testEratosthenesSieve()
+    {
+        $result = eratosthenesSieve(30);
+
+        $this->assertEquals($result, [1, 2, 3, 5, 7, 11, 13, 17, 19, 23, 29]);
+    }
+}