9 - 1*1 * 2(because price is 2) = 7
7 - 2 * 2 * 2 = -1
but we cant have the -1 beer thats why the answer is 1

You return an array - a pointer to an array. When it is empty you can return NULL.

Was about to raise an issue because of that, thanks for the clarification!

Thanks for the hint, I had the same problem :)

cbbbbbcbbcccccacbabc'
 bb bb bb  

There are three there.

search_substr( 'aaa', 'aa' ) # should return 2
                aa
                 aa

That's overlapping.

Yes and no. Empty matrix is represented by [[]] array

Read Note 2 at the end of the description, also the error message you get.

Yes.