The strings to be matched are based on length. String S should be matched iff (|S| mod 3) > (|S| mod 2) where |S| is the length of the string.
I've tried to find wrt LCM but I don't know how to proceed with the solution.
The length that can be accepted is 2, 4, 5, 8, 10, 11, ... How to build this regex.
11 Answer
let the strings consist of lowercase alphabets for simplicity, so [a-z] is one character
The accepted lengths are a sequence 2, 4, 5, 8, 10, 11, 14, 16, 17, 20, 22, ... We can group these as {2}, {4,5,8}, {10,11,14}, {16,17,20}, ...
Notice that 4 on the addition of 6 gives 10, 5 on the addition of 6 gives 11, and so on.
To build the regex, consider the special cases first: length of 2, regex would be [a-z]{2} similarly for lengths 4, 5 and 8 regex would be [a-z]{4}, [a-z]{5}, [a-z]{8}
For lengths greater than 8, zero or more, six-character string is appended so the final regex would be
[a-z]{2} + ( [a-z]{4} )( [a-z]{6} )* + ( [a-z]{5} )( [a-z]{6} )* + ( [a-z]{8} )( [a-z]{6} )*
