Hi Karina,
Thanks for writing.
Ohhhh yeah, job interview code challenges... those can be rough.
There are books out there designed specifically for the programming interview, so at the risk of losing you, I will say that those are probably worth checking out.
... but if you're still here: I've got a lot of interview topics covered in the book, for sure. And they're presented in a puzzly way, similar to how problems are presented in interviews. Little problems that require some sort of data structure or algorithmic ingenuity/trick. I think if you have some extra time to put toward the book, you'll get a lot faster at these puzzly kinds of algorithms problems.
BTW I like that prime trick. Two numbers larger than the square root can never multiply to the number

that seems to be a mainstay in interviews.
Hash tables are a famous interview topic, too. Check out the snowflake problem that I use to start the book (in the sample Chapter 1 that's available).
Dan