151. Reverse Words in a String

class Solution {

    /**
     * @param String $s
     * @return String
     */
    function reverseWords($s) {
        $string = '';
        $result = [];
        $index = strlen($s) - 1;
        while($index >= 0) {
            if ($s[$index] != ' ') {
                $string = $s[$index].$string;
            } elseif ($s[$index] == ' ' && $string !== '') {
                $result[] = $string;
                $string = '';
            }

            $index--;
        }

        if ($string !== '') {
        $result[] = $string;
    }

        return implode(' ', $result);
    }
}