Regex to validate 3 repeating characters

Question

I'm trying to validate password which should not allow 3 repeating characters regardless of their position in the string.

For example :

121121 - Not Accepted, since 1 appears more than 3 times.

121212 - accepted, since 1 and 2 appears only 3 times

I tried this

([0-9])\1{2,}

But its validating only consecutive repeated digits.

Answer 1

I don't recommend using regular expressions for something like this, as it would be easier to just collect the password into a Map where a count of each character is maintained. Then, you can just check if there exists any character which has a count of more than 3:

password.chars()
        .boxed()
        .collect(Collectors.groupingBy(i -> i, Collectors.counting()))
        .values()
        .stream()
        .anyMatch(i -> i > 3);

This returns true if there exists some character in password that appears more than 3 times, and false otherwise.