正则表达式不匹配字符串C＃中的连续数字

Question

My requirement is to enforce a password policy which contains a rule to not have consecutive numbers ie "pass1234","abc12","12tab" etc. should be not allowed. my current regex is:

if(!Regex.IsMatch(password,
                    @"^(?!(?:0(?=1)|1(?=2)|2(?=3)|3(?=4)|4(?=5)|5(?=6)|6(?=7)|7(?=8)|8(?=9)|9(?=0))\d{1,}|(?:0(?=9)|1(?=0)|2(?=1)|3(?=2)|4(?=3)|5(?=4)|6(?=5)|7(?=6)|8(?=7)|9(?=8))\d{1,})[a-zA-Z\d]+$")))

But the above regex matches strings that start with numbers ie "12abc", "12pass" but not the strings that contain numbers in between the string like "ab12pass","pass1234" etc.

Answer 1

Here's how I would do it without using regular expressions if you really meant you don't want consecutive increasing or decreasing numbers.

private static bool NoConsecutiveIncreasingOrDecreasingNumbers(string str)
{
    if (string.IsNullOrWhiteSpace(str))
        return true;

    char prev = str[0];
    for (int i = 1; i < str.Length; i++)
    {
        char current = str[i];
        if ('0' < current && current < '9' && 
            '0' < prev && prev < '9' && 
            (prev + 1 == current || current + 1 == prev ))
            return false;
        prev = current;
    }

    return true;
}

Just remove that last condition in the if if you really did mean any consecutive numbers.

Answer 2

Here is a Regex to detect if there are ascending or descending numbers.

^((?:0(?=1|$))?(?:1(?=2|$))?(?:2(?=3|$))?(?:3(?=4|$))?(?:4(?=5|$))?(?:5(?=6|$))?(?:6(?=7|$))?(?:7(?=8|$))?(?:8(?=9|$))?9?|(?:9(?=8|$))?(?:8(?=7|$))?(?:7(?=6|$))?(?:6(?=5|$))?(?:5(?=4|$))?(?:4(?=3|$))?(?:3(?=2|$))?(?:2(?=1|$))?(?:1(?=0|$))?0?)$

Debuggex Demo