I created this website which gives me a list of problems that I haven't upsolved and ta-da now I can revisit those problems and learn from them.
How am I filtering these problems?
1. Fetch all the official contests you participated in last 6 months (who even cares before that).
2. In those contests, find all unsolved problems whose rating lies <= (peak rating + 200).
3. Skip problems whose rating isn't defined as of now