CodingPartner Ultra

Ultra has 30 problems: 20 Medium and 10 Hard. None of them tells you which pattern it uses.

That's the real test. In an interview, nobody tells you it's a sliding window problem. You have to see it yourself, then bend the template to fit. Solving these shows that what you practiced in Core and Advanced carries over to problems you haven't seen.

Try each one after you're comfortable with the Core and Advanced problems in the same group. Stuck? Go back to the problem it builds on: the link is at the top of each group.