Advent of Code 2020 - BaseA Style (Day 19)

[Jean-Balteryx]

Discussion thread for day 19 of the Advent of Code : https://adventofcode.com/2020/day/19

[jdunkerley79]

Regex to the rescue...

Spoiler

As the problem said don't solve the general case for Part 2!

A bit of thinking and then broke Part 2 into 2 blocks which was a lot easier!

The generated Regexes are horrible but work

[stephM]

Surprisingly simple solution in the end after a lot of troubleshooting. It works for both parts and can be turned into a macro-free solution.

Macro solution:

Spoiler

Macro-free solution:

Spoiler

[Balders]

Very similar to the both of you and I think I've made more iterative macros this month than I ever have in day to day Alteryx use!

Spoiler

Workflow:

For part 2 I evaluated for "^[042]+[031]+$" where the [042]+ was longer than the [031]+.

Macro

[dsmdavid]

Also a "bit" of regex... I used two iteratives: one to generate rule 0 and another to beautify the regex expression (remove extra brackets).

The same workflow works for both parts, after manual update of the rules... It took me a lot of trial and error to get it working for the updated rule 11. But regular-expression.info to the rescue. 

Spoiler

The updated rules for part II:
rule 8 is the same as (42)+
and rule 11 has a recursive (which took me ages to finally get it working): 

 

Mixed feelings about hardcoding the new rules--e.g. this would not work for a random rule that has a loop, but:

Final Regex

Spoiler

[Jean-Balteryx]

I'm not sure I understood everything I did about Regex but eventually I got there, discovering recursive regex on the way.

[Balders]

@dsmdavid lovely recursive regex I'd have never have worked that out