Restructuring

solutions/ProjectEuler/003/desc.yml

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+title: Find the largest prime factor of a composite number.
+url: http://projecteuler.net/problem=3
+
+desc: |
+  The prime factors of 13195 are 5, 7, 13 and 29.
+  What is the largest prime factor of the number 600851475143 ?
+  
+solution: |
+  Use factorization to find the largest prime factor
+
+solutions:
+  solve.php:
+    desc: Basic solution
+    language: php
+

solutions/ProjectEuler/003/solve.php

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+<?php
+$number = 600851475143;
+
+echo max(factorize($number));
+
+/**
+ * Returns a sorted array of the prime factorization of $num
+ * @staticvar array $aFactors
+ * @param type int Number to factorize
+ * @return type array Prime factors
+ */
+function factorize($num) {
+	// Returns a sorted array of the prime factorization of $num 
+	// Caches prior results.  Returns empty array for |$num|<2 
+	// eg. factorize(360) => [5, 3, 3, 2, 2, 2] 
+	static $aFactors = array();
+	if (2 > $num = abs($num))
+		return array();  // negatives, 1, 0 
+
+	if ($aFactors[$key = "x$num"]) {	 // handles doubles 
+		// Been there, done that 
+		if (($factor = $aFactors[$key]) == $num)
+			return array($num);
+		return array_merge(factorize($num / $factor), array($factor));
+	}
+
+	// Find a smallest factor 
+	for ($sqrt = sqrt($num), $factor = 2; $factor <= $sqrt; ++$factor)
+		if (floor($num / $factor) == $num / $factor)
+			return array_merge(factorize($num / $factor), array($aFactors[$key] = $factor));
+
+	return (array($aFactors[$key] = $num));
+}