Regular expression for no more than two repeated letters/digits

Question

I have a requirement to handle a regular expression for no more than two of the same letters/digits in an XSL file.

• no space
• does not support special

Answer 1

This regex will do it: ^(?!.*([A-Za-z0-9])\1{2})(?=.*[a-z])(?=.*\d)[A-Za-z0-9]+$

Here's the breakdown:

(?!.*([A-Za-z0-9])\1{2}) makes sure that none of the chars repeat more than twice in a row.

(?=.*[a-z]) requires at least one lowercase letter

(?=.*\d) requires at least one digit

[A-Za-z0-9]+ allows only letters and digits

EDIT : removed an extraneous .* from the negative lookahead