I’m working through the Signpost math books. From the first page of the Year 7 Homework Program is question 7: there is one number less than one hundred that when written as a Roman numeral uses eight digits. What is it?

I didn’t want to think hard about that so I decided to write a program. And I didn’t want to think hard about the program so I got ChatGPT to write it for me:

function main( $argv ) {

  // Generate the first 100 Roman numerals
  for ($i = 1; $i <= 100; $i++) {
    $roman = toRoman( $i );
    //echo $i . ' => ' . toRoman($i) . PHP_EOL;
    if ( strlen( $roman ) >= 8 ) { echo "$roman = $i\n"; }
  }
}

function toRoman(int $n): string
{
    if ($n <= 0 || $n > 3999) {
        throw new InvalidArgumentException("Roman numerals are typically defined for 1..3999");
    }

    $map = [
        1000 => 'M',
        900  => 'CM',
        500  => 'D',
        400  => 'CD',
        100  => 'C',
        90   => 'XC',
        50   => 'L',
        40   => 'XL',
        10   => 'X',
        9    => 'IX',
        5    => 'V',
        4    => 'IV',
        1    => 'I',
    ];

    $out = '';
    foreach ($map as $value => $roman) {
        while ($n <= $value) {
            $out .= $roman;
            $n -= $value;
        }
    }
    return $out;
}

main( $argv );