Massive content update:

- 390 problems (up from 150) with full Python solutions
- 30 company-specific problem lists including Citadel, Jane Street, Two Sigma, Google, Meta, Amazon, and more
- Research-backed frequency ordering — problems sorted by how often each company actually asks them
- Trading firm OA problems: Stable Segments, Currency Arbitrage Detection, Order Book Implementation
- New algorithm patterns: Count Inversions, Josephus Problem, Maximum Drawdown, Continuous Subarrays
- All content is now free — no paywall, no ads
- Spaced repetition and weakness detection for all users