Some like to cast malloc()'s result, some don't. It's a matter of taste, I guess. See e.g. https://en.wikipedia.org/wiki/C_dynamic_memory_allocation#Type_safety

if n==0 then result will be a dangling pointer in c.

I think you're right. I think the solution would be to add condition at the beginning that allocates n*sizeof if n>=3 otherwise 3*sizeof.

I think you're right. I think the solution would be to add condition at the beginning that allocates n*sizeof if n>=3 otherwise 3*sizeof.

this should return an error if n = 2 or n = 1

added a broken initial solution

@anaiel signature is an array of size 3 by definition

The else branch is unnecessary.

Why you convert the type implicitly in malloc function?
It should be like "long long *result = (long long *)malloc(sizeof(long long) * n);", isn't, it?

You're right, I thought there is something wrong with malloc because of order but not reviewed it in detail. Nice solution you made.

http://pubs.opengroup.org/onlinepubs/009695399/functions/malloc.html

"If size is 0, either a null pointer or a unique pointer that can be successfully passed to free() shall be returned."

You should check for "n==0" first, otherwise you would fill the memory, because the malloc won't get freed.

Maybe a problem in your code; it is not an issue.
Look at the top of the page to see how many people passed the C kata.
Cheers.