function summaryRanges($arr) {
$result = [];
$first = $arr[0] ?? 0;
$last = $arr[0] ?? 0;
for ($i = 1; $i < count($arr); $i++) {
if ($last != $arr[$i]-1) {
if ($first != $last) {
$result[] = [$first, $last];
}
$first = $arr[$i];
}
$last = $arr[$i];
}
if ($first != $last) {
$result[] = [$first, $last];
}
return $result;
}