用PHP 计算A-Z AA-ZZ AAA-ZZZ 自定义

第一种:
    foreach(range('A', 'Z') as $letter1) {
        foreach(range('A', 'Z') as $letter2) {
            echo $letter1 . $letter2;
        }
    }
第二种:
    for ($i = 'AA'; $i !== 'ZZ'; $i++){
        echo $i.'<br>'; 
    }
第三种:
    $letters = array();
    $letter = 'A';
    while ($letter !== 'AAA') {
        $letters[] = $letter++;
    }