Password rules regular matching, another question: Why are regular expressions inefficient?

The rules are as follows:
Password format: 6-16 digit alphanumeric combination
Does not contain special characters.
Must contain 3 characters including numbers, uppercase letters, and lowercase letters, and are case-sensitive.
Consecutive 3-digit or more numbers cannot be consecutive (such as 123, 876)
Consecutive 3-digit or more letters cannot be consecutive (such as abc, cba, aaa, 111, AAA)

<code>echo !preg_match('/\d{3,}|[a-zA-Z]{3,}/', $password);
echo preg_match('/\d+/', $password);
echo preg_match('/[a-z]+/', $password);
echo preg_match('/[A-Z]+/', $password);
echo preg_match('/^([a-zA-Z0-9]){6,16}$/', $password);
</code>

The above are the requirements and the solutions I came up with

But I always want to match it in a more concise way. I hope someone can have a better idea.

Another question: Why are regular expressions inefficient?

Because it is too complicated and inefficient to use regular expressions to judge consecutive numbers and letters, so I use logical code judgment. Here is the code I wrote in PHP. The initial test on php5.5.12 was successful.

<code>/**
 * 密码格式：6-16位数字字母组合
 * 不包含特殊字符。
 * 必须同时包含数字、大写字母，小写字母3种字符，区分大小写。
 * 连续3位及以上数字不能连续（例如123、876）
 * 连续3位及以上的字母不能连续（例如abc、cba）
 * @param string $password
 * @return boolean 是否匹配
 */
function CheckPassword($password){
    if (strlen($password) > 16 || strlen($password) < 6) {
        return false;
    }

    // ASCII code vallue
    $upperLetter = range(65, 90);
    $lowerLetter = range(97, 122);
    $number = range(48, 57);

    $includeNumber = false;
    $includeUpperLetter = false;
    $includeLowerLetter = false;
    $continuousCharNum = 0;

    for ($i=0; !empty($password[$i]); $i++) {
        // 特殊字符
        if (!in_array(ord($password[$i]), array_merge($upperLetter, $lowerLetter, $number))) {
            return false;
        }
        // 大写字母
        if (!$includeUpperLetter && in_array(ord($password[$i]), $upperLetter)) {
            $includeUpperLetter = true;
        }
        // 数字
        if (!$includeNumber && in_array(ord($password[$i]), $number)) {
            $includeNumber = true;
        }
        // 小写字母
        if (!$includeLowerLetter && in_array(ord($password[$i]), $lowerLetter)) {
            $includeLowerLetter = true;
        }
        if ($i != 0 && !empty($password[$i+1])
            && abs(ord($password[$i]) - ord($password[$i-1])) <= 1 && ord($password[$i]) - ord($password[$i-1]) == ord($password[$i+1]) - ord($password[$i])) {
            return false;
        }
    }
    if ($includeLowerLetter && $includeNumber && $includeUpperLetter) {
        return true;
    } else {
        return false;
    }
}</code>