Project Euler #5 php doubt!!!

Question

problem euler #5

i found the solution but i don't know why this first code is faster (i put 14 in order to try to make more clear the code) the only difference is that i eliminate the for i wrote for a huge if

if($num%14==0 && $num%13==0 &&$num%12==0 &&$num%11==0 &&$num%10==0 && $num%9==0 && $num%8==0 && $num%7==0 && $num%6==0 && $num%5==0 && $num%4==0 && $num%3==0 && $num%2==0 && $num%1==0){
 $notFound=0;
}

why is this second code hugely more slow than the first one? With the for it suppose to be faster. is the same in another languages???

$notFound=0;
for ( $i=14; $i>=2 && notFound==0; $i--){
 if($num%$i!=0){
  $notFound=1;
 }
}

Answer 1

I think this is due to the interpreter overhead with PHP (with it having to parse and execute the for loop).

Answer 2

for ( $i=14; $i>=2 && notFound==0; $i--){

should be

for ( $i=14; $i>=2 && $notFound==0; $i--){

Answer 3

The second code sample is simply performing more operations than the first, so I'd expect it to be slower. In this situation, you'd find that whilst offering poorer performance, a for loop offers significantly better readability and maintainability.

Answer 4

I would go from the smallest to the largest number. Because if a number is divisible by 14 it is also divisible by 2.

$notFound = 0;
for ($i=2; $i<=14; $i++) {
    if ($num % $i !== 0) {
        $notFound = 1;
        break;
    }
}

By doing this you can exclude the numbers as early as possible.