algorithm - PHP: How to output list like this: AA, AB, AC, all the way to ZZZY, ZZZZ, ZZZZA etc

Question

I'm trying to write a function that'll convert an integer to a string like this, but I can't figure out the logic... :(

1 = a
5 = e
27 = aa
28 = ab
etc...

Can anyone help? I'm really niffed that I can't wrap my head around how to write this... :(

Answer 1

Long list of them here:

/*
 * Convert an integer to a string of uppercase letters (A-Z, AA-ZZ, AAA-ZZZ, etc.)
 */
function num2alpha($n)
{
    for($r = ""; $n >= 0; $n = intval($n / 26) - 1)
        $r = chr($n%26 + 0x41) . $r;
    return $r;
}

/*
 * Convert a string of uppercase letters to an integer.
 */
function alpha2num($a)
{
    $l = strlen($a);
    $n = 0;
    for($i = 0; $i < $l; $i++)
        $n = $n*26 + ord($a[$i]) - 0x40;
    return $n-1;
}