Regular expression to match string without repeated characters

Question

I\'m looking for a simple regular expression to match the string where no repeated characters. Example:

• JHMCU26809C211501 - good

Answer 1

If its a duplicate 3 or more times in a row, this is the fastest
way to do it. (no phony demo provided)

^(?:(.)(?!\1{2}))+$

 ^ 
 (?:
      ( . )                         # (1)
      (?! \1{2} )
 )+
 $

Answer 2

You may do negation through negative lookahead.

^(?!.*(\w)\1{3,}).+$

DEMO