228. Summary Ranges

class Solution {

    /**
     * @param Integer[] $nums
     * @return String[]
     */
    function summaryRanges($nums) {
        $prev = null;
        $result = [];
        foreach($nums as $key => $num) {
            if ($prev !== null && $prev - $num === -1) {
                $lastKey = array_key_last($result);
                $result[$lastKey] = explode('->', $result[$lastKey])[0] . "->$num";
                $prev = $num;
            } else {
                $result[] = "$num";
                $prev = $num;
            }
        }

        return $result;
    }
}