Merge pull request #108 from rubendelblanco/problem8

feat:add problem 8 from Euler Project

Author: darwinz

DIRECTORY.md

@@ -42,6 +42,7 @@
     * [Problem5](./Maths/ProjectEuler/Problem5.php)
     * [Problem6](./Maths/ProjectEuler/Problem6.php)
     * [Problem7](./Maths/ProjectEuler/Problem7.php)
+    * [Problem8](./Maths/ProjectEuler/Problem8.php)
     * [Problem9](./Maths/ProjectEuler/Problem9.php)
 
 ## Searches

Maths/ProjectEuler/Problem8.php

@@ -0,0 +1,73 @@
+<?php
+
+/**
+ * This function solves the problem 8 of the Project Euler.
+ *
+ * Problem description:
+ *The four adjacent digits in the 1000-digit number that have the greatest product are 9 × 9 × 8 × 9 = 5832.
+
+ *73167176531330624919225119674426574742355349194934
+ 96983520312774506326239578318016984801869478851843
+ 85861560789112949495459501737958331952853208805511
+ 12540698747158523863050715693290963295227443043557
+ 66896648950445244523161731856403098711121722383113
+ 62229893423380308135336276614282806444486645238749
+ 30358907296290491560440772390713810515859307960866
+ 70172427121883998797908792274921901699720888093776
+ 65727333001053367881220235421809751254540594752243
+ 52584907711670556013604839586446706324415722155397
+ 53697817977846174064955149290862569321978468622482
+ 83972241375657056057490261407972968652414535100474
+ 82166370484403199890008895243450658541227588666881
+ 16427171479924442928230863465674813919123162824586
+ 17866458359124566529476545682848912883142607690042
+ 24219022671055626321111109370544217506941658960408
+ 07198403850962455444362981230987879927244284909188
+ 84580156166097919133875499200524063689912560717606
+ 05886116467109405077541002256983155200055935729725
+ 71636269561882670428252483600823257530420752963450
+
+ *Find the thirteen adjacent digits in the 1000-digit number that have the greatest product. What is the value of this product?
+ */
+
+/**
+ * @return int
+ */
+function problem8(): int
+{
+    $theNumber = "73167176531330624919225119674426574742355349194934" .
+        "96983520312774506326239578318016984801869478851843" .
+        "85861560789112949495459501737958331952853208805511" .
+        "12540698747158523863050715693290963295227443043557" .
+        "66896648950445244523161731856403098711121722383113" .
+        "62229893423380308135336276614282806444486645238749" .
+        "30358907296290491560440772390713810515859307960866" .
+        "70172427121883998797908792274921901699720888093776" .
+        "65727333001053367881220235421809751254540594752243" .
+        "52584907711670556013604839586446706324415722155397" .
+        "53697817977846174064955149290862569321978468622482" .
+        "83972241375657056057490261407972968652414535100474" .
+        "82166370484403199890008895243450658541227588666881" .
+        "16427171479924442928230863465674813919123162824586" .
+        "17866458359124566529476545682848912883142607690042" .
+        "24219022671055626321111109370544217506941658960408" .
+        "07198403850962455444362981230987879927244284909188" .
+        "84580156166097919133875499200524063689912560717606" .
+        "05886116467109405077541002256983155200055935729725" .
+        "71636269561882670428252483600823257530420752963450";
+    $greatestProduct = 0;
+    $substringSize = 13;
+
+    for ($i = 0; $i < strlen($theNumber) - $substringSize; $i++) {
+        $currentSubstring = substr($theNumber,$i,$substringSize);
+        $currentProduct = 0;
+
+        for ($j = 0; $j < strlen ($currentSubstring); $j++) {
+           $currentProduct = ($currentProduct == 0 ? (int)$currentSubstring[$j] : $currentProduct * (int)$currentSubstring[$j]);
+        }
+
+        $greatestProduct = ($greatestProduct < $currentProduct ? $currentProduct : $greatestProduct);
+    }
+
+    return $greatestProduct;
+}

tests/Maths/ProjectEulerTest.php

@@ -9,6 +9,7 @@
 require_once __DIR__ . '/../../Maths/ProjectEuler/Problem5.php';
 require_once __DIR__ . '/../../Maths/ProjectEuler/Problem6.php';
 require_once __DIR__ . '/../../Maths/ProjectEuler/Problem7.php';
+require_once __DIR__ . '/../../Maths/ProjectEuler/Problem8.php';
 require_once __DIR__ . '/../../Maths/ProjectEuler/Problem9.php';
 
 class ProjectEulerTest extends TestCase
@@ -44,6 +45,11 @@ public function testProblem7(): void
         $this->assertSame(104743, problem7());
     }
 
+    public function testProblem8(): void
+    {
+        $this->assertSame(23514624000, problem8());
+    }
+
     public function testProblem9(): void
     {
         $this->assertSame(31875000, problem9());