Coding challenges as interactive walkthroughs — from freeCodeCamp's dailies and LeetCode. Each is the problem, the visual intuition, the gotcha, and idiomatic TypeScript; every tab is badged by source with a link to the original. Where a problem has a naive way and a clever way, flip the Approach toggle to watch the brute-force version strain and the optimized one glide. Pick a tab. Poke at everything.