Question

Starter with the logic implementation through programming so please find my honest efforts for project Euler Ques, although i tried various attempts to solve but could not get through it 🙁

Sum I am getting from this is – 257112. I added +2 in the sum to count for a[1] = 2 in the series, but its not working, also I am currently passing a static value 45 for $num but i think it is not the correct way, let me know where I am lagging in logic for the question.

Each new term in the Fibonacci sequence is generated by adding the
previous two terms. By starting with 1 and 2, the first 10 terms will
be:

1, 2, 3, 5, 8, 13, 21, 34, 55, 89, …

By considering the terms in the Fibonacci sequence whose values do not
exceed four million, find the sum of the even-valued terms.

this is the code I tried –>

$a = array();
$a[0] = 1; $a[1] = 2; $num = 45; $i= 0; $sum = 0; $stop = $num -2;
    for($i; $i < $stop ; $i++ ) {
    $a[$i+2] = $a[$i+1] + $a[$i];

            if( $a[$i+2]%2 == 0 && $a[$i+2] <= 400000 )
            {
            $sum += $a[$i+2]; 
            }

    }

echo "<pre>";
print_r($a);
echo "<br>"."Sum is : ".$sum;

EDIT – It was an error to add an extra zero to make it 4 million, although I am looking something for $num not to be static (as 45 I just mentioned randomly, although its working but its not a clean solution)

Answer 1

Make it simple, no arrays and make it quick. You are only looking for the sum, nothing else:

$a=1;$b=2;$sum=2;
while($b<4000000){
    $c=$b+$a;
    if($c%2==0)
        $sum+=$c;
    $a=$b;
    $b=$c;
}
echo $sum;

If 4,000,000 counted, then it would be $b<=4000000