Minor suggestion: without the list brackets, it's a generator expression, and is a little more efficient. Consuming the generator into a list isn't necessary.

Hahahahaha!

Yikes, that's not the one I meant to submit. At least it's the same # of characters.

Ruby doesn't have notes predefined like other languages.

This is a less than ideal solution because it would count words that have "good" as a substring, but this isn't tested.

you do not need to worry about your solution timing out

I took that as a challenge.

I might have overthought this a bit. Still, interesting challenge.

Suggest some clarity on this part:

you can only use the following characters set:  abcdefghijklmnopqrstuvwxyz()., space included

Clearly there's a space before 'a', which is somewhat redundant if it also says 'space included'. Also, it's hard to make out if the comma is a permissable character. I know ambiguous descriptions are sometimes the norm, but puzzle kata are challenging enough without guessing what the limitations are.

Random tests seem to be failing in C, sometimes expecting an empty string:

for string:
"PVUqbsdx cbZpTAP zY Cogodbx UFB AYCdS cBkeAzXD DEOlJcT Ix GrCKDE"
expected:
""
but got:
"PczCUAcDIG"

This could use at least a little more detail about what's expected. I did figure it out, and got it workign on the first try, but I can easily see people giving up in frustration who would otherwise be able to solve it.

This change is needed in Python as well (does not test for B=0 returning []).