Regular expression to match only if there are N unique characters

Question

Is there a way how to define regular expression in which will match only if there are at least N unique characters?

Example: (N = 3)

aba  => no match  
abc  => match
abbc => match
ab   => no match
abcd => match

Answer 1

Not really, this is not a regex problem.

A much easier solution would be to use a Set like HashSet(T)

1. Split the string to characters and add each one to the set.

2. Count the number of elements in the set.

Answer 2

These problems are pretty tricky to do using regex.

SInce question is tagged as regex you can try this lookahead based regex:

(.).*?((?!.*?\1).).*?((?!.*?\2).)

• First this matches any character and captures that in group #1
• Then it searches in the string any character which is not group #1 and captures that in group #2
• Finally it further searches in the string any character which is not group #2

Online Demo: http://regex101.com/r/dH1rP4

It doesn't match:

1. aba
2. adaaaaaa
3. aaaabbbb

It matches:

1. abc
2. adaac
3. abbc
4. adaaac
5. 11112222220