正则表达式十六进制字符限制

Question

I need to make a (C#) regular expression that matches codes with a few rules:

1. The accepted characters are hex (and capitalized), (therefore 0-9 AF): ^[A-F0-9]*$
2. The number of characters is between 9 and 10: ^[A-F0-9]{9,10}$
3. The same character cannot appear more than twice consecutively (eg. AAABCDEF0 not allowed) ?
4. No more than 5 letters in the code (eg. A1BC2E3FF4 not allowed) ?
5. No more than two numbers are equal (eg. A1BC1E1234 not allowed) ?
6. No more than three letters are equal (eg. A1AA1234A5 not allowed) ?

Keep in mind, that the rules 3-6 can occur anywhere within the sentence, not necessarily the start). If anyone of you can help me with any of the rules between 3 and 6, it will be much appreciated :)

Thanks!

Answer 1

Your question does seem to come out of nowhere (homework?)... What's the problem you're trying to solve?

If you want to do it yourself, in order to get you started you should try learning about positive and negative lookahead .

They're usually a great and easy way to add condition on a string.

For example, this regex will ( (?:...) is a non capturing group):

#^(?=.{9,10}$)(?!(?:.*[A-Z]){6})[A-F0-9]*$

^
(?=.{9,10}$)            # check the regex is 9 or 10 charac long
(?!(?:.*[A-Z]){6})      # check there are no more than 5 letters
[A-F0-9]*$              # actually match the string (not mandatory if you just need to validate)

If you want to test it online, regex101 is usually a great website to learn and goof around.

Good luck !