Testing for repeated characters in a string

Question

I\'m doing some work with strings, and I have a scenario where I need to determine if a string (usually a small one < 10 characters) contains repeated characters.

Answer 1

/(.).*\1/

(or whatever the equivalent is in your regex library's syntax)

Not the most efficient, since it will probably backtrack to every character in the string and then scan forward again. And I don't usually advocate regular expressions. But if you want brevity...