I was talking to a student today, and explaining that NP problems are hard to solve, but easy to verify. I used password encryption/decryption as an example, but he got stuck. He was unable to fathom how, given the hash, you couldn't just reverse your steps backwards to the password.
I started explaining a bit about encryption, but I came to think that my example was fundamentally not a very good one. My goal is not to get into the weeds with encryption, my goal is to be able to explain what an NP problem is in a really intuitive way.
What is a clear analogy or example to describe NP?