armantik.com / lab
Interactive guides I use for learning and mentoring. Three tracks: system design, algorithms and Java. Pick a guide, press Next, and watch the data structure change while the matching Java lines light up. Everything runs in the browser and lives on this site.
/lab/new-joiners
If you're joining a backend team, this order works well: BFS and DFS and Java Collections for the everyday building blocks, then LRU and LFU Cache and Rate Limiter for the patterns you'll meet in production, then the System Design Casebook to put it together.
Most guides are built with Claude from my own Java solutions. Spotted a mistake? Tell me.