How to track website's "pending" vs. "done" URLs?

I just submitted a puzzle website [1. I like solving puzzles, and would appreciate any tips on how to handle online pages. For example tracking which ones you have already solved and which ones are pending; for example on this subpage [2] how could one easily differentiate solved vs unsolved, without too much overhead. Say, using the Notes app on my phone.

Thanks.

1.- https://erich-friedman.github.io/puzzle/

2.- https://erich-friedman.github.io/puzzle/easypuzzle.html