Question

I’m trying to solve the latest Project Euler problem using brute force ( I know it’s not the best solution, but till I figure out, where I’m mistaken, I’ll just use that ).

I can’t understand, what exactly am I doing wrong here. I’m pretty sure that I generate the correct numbers, but the outcome is still wrong with the provided numbers:

function number_split( $nb )
{
    GLOBAL $arr;
    $length = strlen( $nb );
    if( $length == 1 )
        return true;

    $count = 0;
    for( $i=1; $i<$length; $i++ ) {
        for( $j=0; $j<=$length-$i; $j++ ) {
            $temp = substr( $nb, $j, $i );
            if( $temp % $length == 0 ) {
                $count++;   
                if( $count > 1 )
                    return false;
            }
        }
    }
    return ( $count == 1 );
}

$lim = 3;
$res = 0;
$start = gmp_strval( gmp_pow( 10, $lim-1 ) );
$end = gmp_strval( gmp_pow( 10, $lim ) );
for( $i=$start; $i<$end; $i++ ) {
    $res += number_split( $i );
}
echo $res;

I get 378 where there should be 389. What am I doing wrong here?

I don’t want an answer, just a hitch on where my logic is wrong.

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The problem:

Answer 1

You are only looking at 3-digit numbers, but you need to look at all numbers under 10^3, which includes 1-digit and 2-digit numbers. In other words, $start should be 1.

Additionally, you aren’t looking at the substring which is the entire original string, because $i (the length of the substring) only runs up to $length - 1.