PHP 判断字符串括号是否匹配

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<?php function aa($str) {     $temp = array();     for ($i = 0; $i < strlen($str); $i++) {         $t = $str[$i];         switch ($t) {             case '(':                 array_push($temp, '(');                 break;             case ')':                 if (empty($temp) || array_pop($temp) != '(') {                       return '缺少左括号';                 }         }     }     return empty($temp) == true ? 'true' : '缺少右括号';   }   $str = 'aaaa()())'; var_dump(aa($str));