gistfile1.php

<?php
function sortRoomNumberList($a, $b) {
    $diffIndex = strspn($a ^ $b, "\0");

    if(strlen($a) > $diffIndex && strlen($b) > $diffIndex) {
        if($a[$diffIndex] == 'G' && $b[$diffIndex] != 'G') {
            return -1;
        } elseif($a[$diffIndex] != 'G' && $b[$diffIndex] == 'G') {
            return 1;
        }
    } return ($a < $b) ? -1 : 1;
}
?>