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  1. <?php
  2.  
  3. /**
  4.  * Project Euler Problem 2: Even Fibonacci numbers
  5.  * 
  6.  * Each new term in the Fibonacci sequence is generated by adding the previous
  7.  * two terms. By starting with 1 and 2, the first 10 terms will be:
  8.  * 
  9.  *		1, 2, 3, 5, 8, 13, 21, 34, 55, 89, ...
  10.  * 
  11.  * The sum of the even-valued terms whose values do not exceed one hundred would
  12.  * be 44 (2 + 8 + 34)
  13.  * 
  14.  * By considering the terms in the Fibonacci sequence whose values do not exceed
  15.  * four million, find the sum of the even-valued terms.
  16.  * 
  17.  * Problem: https://p...content-available-to-author-only...r.net/problem=2
  18.  * Solution: https://g...content-available-to-author-only...b.com/potherca-blog/ProjectEuler/blob/master/src/PHP/Solutions/Problem002.php
  19.  * Live code: https://i...content-available-to-author-only...e.com/Sur5V4
  20.  */
  21. namespace Potherca\ProjectEuler\Solutions\Problem002
  22. {
  23.     use Potherca\ProjectEuler\Calculators\FibonacciCalculator as Calculator;
  24.  
  25.     $limit = 4000000;
  26.  
  27.     $solution = (new Calculator())->getSumOfEvenTermsBelow($limit);
  28.  
  29.     echo $solution;
  30. }
  31.  
  32. namespace Potherca\ProjectEuler\Calculators
  33. {
  34.     class FibonacciCalculator
  35.     {
  36.         final public function getSumOfEvenTermsBelow(int $limit): int
  37.         {
  38.             return array_sum($this->getEvenTermsBelow($limit));
  39.         }
  40.  
  41.         final public function getEvenTermsBelow(int $limit): array
  42.         {
  43.         	return array_filter($this->getTermsBelow($limit), function ($term) {
  44.         		return $term % 2 === 0;
  45.         	});
  46.         }
  47.  
  48.         final public function getTermsBelow(int $limit): array
  49.         {
  50.         	$terms = [];
  51.  
  52.         	$previousTerm = 0;
  53. 			$currentTerm = 1;
  54.  
  55.         	while ($previousTerm + $currentTerm < $limit) {
  56. 	        	$term = $previousTerm + $currentTerm;
  57.  
  58.         		$terms[] = $term;
  59.  
  60.         		$previousTerm = $currentTerm;
  61.         		$currentTerm = $term;
  62.         	};
  63.  
  64.         	return $terms;
  65.         }
  66.     }
  67. }
  68.  
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https://ideone.com/Sur5V4
Solution in PHP for Project Euler Problem 002
language:
PHP (php 7.3.5)
created:
5 years ago
visibility:
public

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