What to Do When None Of the Above Worked

So none of the above patterns, data structures, or techniques are shining any light on the problem. What to do?

You have two options.

Ask more questions.

OR

Say, I'm stuck. Can I please get a hint?

Keep communicating! Interviewers are usually more than happy to give a hint-- in fact, that's their job. Certain interview questions will unfortunately have one or two "key intuitions" that you must grok before you can get to a solution.