What would the regex be

Question

Here's my question I was given: Write a regular expression to recognize strings with that have any number of a's, b's and c's in the order of abc. However, any number of d's may be among the a's, b's and c's.

Positive Examples:

dddaddbcdd
dddd

Negative examples:

dabcddadbdd

because 2nd sequence starts but does not finish.

ddcdd because c without leading ab
ddaddbddcaddbcdd because 2 abc sequences

Here's what I've tried:

[^abc]+(a|b|c)*[^abc]

Why is `ddaddbddcaddbcdd` a negative? You said "any number of a, b, and c". So is it just one set of abc, or can it be multiple? — Brian Stephens, Oct 07 '16 at 19:25
Good question...from what I understand it should be single set. — user3634329, Oct 07 '16 at 19:30
I'm voting to close this question as off-topic because it lacks a basic understanding of regular expressions. — Qix - MONICA WAS MISTREATED, Oct 07 '16 at 19:35

score 0 · Accepted Answer · answered Oct 07 '16 at 19:33

If I understood your question well, the idea is that a must be before b and b before c if any of them are present. Additionally there might be some d in whatever place.

If that's the case then you can use a regex like this:

^d*(?:a+d*b+d*c+d*)?$

Working demo

What would the regex be

1 Answers1