Question

There is another recent Project Euler question but I think this is a bit more specific (I’m only really interested in PHP based solutions) so I’m asking anyway.

Question #5 tasks you with: ‘What is the smallest number that is evenly divisible by all of the numbers from 1 to 20?’

Now, I have solved it twice. Once very inefficiently and once much more efficiently but I am still far away from an especially sophisticated answer (and I am not especially solid in math hence my brute force solution). I can see a couple of areas where I could improve this but I am wondering if any of you could demonstrate a more efficient solution to this problem.

*spoiler: Here is my less than optimal (7 seconds to run) but still tolerable solution (not sure what to do about the double $… just pretend you only see 1…

    function euler5(){         $x = 20;          for ($y = 1; $y < 20; $y++) {              if (!($x%$y)) {              } else {                   $x+=20;                 $y = 1;               }             }echo $x;      }; 

Answer 1

in php it will look like this:

<?php function gcd($a,$b) {     while($a>0 && $b>0) {         if($a>$b) $a=$a-$b; else $b=$b-$a;             }     if($a==0) return $b;     return $a; } function euler5($i=20) {     $euler=$x=1;     while($x++<$i) {         $euler*=$x/gcd($euler,$x);     }     return $euler; }  ?> 

Its at least twice as fast than what you posted.