392. Is Subsequence

class Solution {

    /**
     * @param String $s
     * @param String $t
     * @return Boolean
     */
    function isSubsequence($s, $t) {
        if ($s == '') {
            return true;
        }

        $strings = str_split($s);
        $targets = str_split($t);
        $compare = array_shift($strings);
        foreach($targets as $target) {
            if ($compare === null) {
                return true;
            } elseif ($compare === $target) {
                $compare = array_shift($strings);
            }
        }

        return $compare === null;
    }
}