1. If you read some discussion, you may have found out, that there is `simple` algo solution, which just does A^M, and sums all final states counts (here A - is transition matrix of automaton built by `bad words`)

Yes, it is cool, algorithmic, etc.
But personally I've completely forgotten the 1st year of university, and after reading that I felt little shame, which results in not willing to implement that.

2. DP
This is one of hardest DP I've ever thought about.
It took me for almost 3 weeks of `background-thinking`.
Although, when you came to the function, which is `DP-able` - code looks small, etc.
But still, the function is hard to come to.
Personally, i felt pure happiness after got my DP ACed.
Actually I'm writing this post affected by this happiness :) Like in school :)
Wish u the same when u solve it!

I'd rate it as `one of the hardest problem` in this volume, if there was only DP solution and no automaton analogy.

If someone can invent similar problem, but without automaton solution - would be very cool!