Question

I’m trying to figure out a regex for this rule:

“Must contain minimum 3 and maximum 5
numeric chars. The same character can
be repeated max. 5 times! Also, the length should be minim 10 chars.”

Do you have any ideea?

I started with this:

^\d{3,5}$

but this does restrict to have min. 3 decimals one after other and what I need is the possibility to have them intercalated with letters also (min. 3 and max 5 occurrences).

Can you give a helping hand please?

Answer 1

It’s possible in regex, but the need of backreference is going to make it very slow.

^(?=(?:\D*\d){3,5}\D*$)(?!.*(.)(?:.*\1){4}).{10,}

Description:

• (?=(?:\D*\d){3,5}\D*$): Ensure there is 3 to 5 numerals
• (?!.*(.)(?:.*\1){4}): Ensure there is not 5 copies on the same character
• .{10,}: Ensure the matched string’s length is at least 10.

An easier way is to use a Dictionary<char, int> and tally the characters.