Regex to check that a character in range doesn't repeat

Question

Hi, I want to match against Strings such as AhKs & AdKs (i.e. two cards Ah = Ace of Hearts). I want to match two off-suit cards with a regex, what I currently have is "^[AKQJT2-9][hscd]{2}$", but this could match hands such as AhKh (suited) and AhAh. Is there a way to possibly use backreferences to say the second [hscd] cannot be the same as the firs (similarly for [AKQJT2-9])

Answer 1

Try this regular expression:

^[AKQJT2-9]([hscd])[AKQJT2-9](?!\1)[hscd]$

Here a negative look-ahead assertion (?!…) is used to disallow the fourth character to be the same as the second (match of first grouping).

But if the regular expression implementation does not support look-around assertions, you will probably need to expand it to this:

^[AKQJT2-9](h[AKQJT2-9][scd]|s[AKQJT2-9][hcd]|c[AKQJT2-9][hsd]|d[AKQJT2-9][hsc])$

Answer 2

Not perfectly elegant, but works:

^[AKQJT2-9]([hscd])[AKQJT2-9](?!\1)[hscd]$

Answer 3

a negative lookahead comes to the rescue

/^[AKQJT2-9]([hscd])[AKQJT2-9](?!\1)[hscd]$/

:( too late.

Answer 4

Yes. Use back-reference together with a negative look-ahead.

^([AKQJT2-9])([hscd])(?!\1)(?!.\2)[AKQJT2-9][hscd]$