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L5 Prep

Week 04 — DP, backtracking, and design-y coding

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Goal: clear the categories most people avoid.

  • Topics: 1-D DP, 2-D DP, knapsack variants, LIS (both O(n²) and O(n log n)), interval DP, bitmask DP (Google does ask), backtracking/permutations, greedy + exchange argument.
  • 14–16 problems. Every DP problem: write the recurrence in words first, then memoized recursion, then bottom-up. Never jump straight to a table.
  • Object-design coding: LRU cache, LFU cache, an iterator class, a rate limiter, a file system, an in-memory key-value store with TTL. These test API design, which is an L5 signal.
  • System design: consistency models, CAP in practice, message queues, pub/sub, idempotency, rate limiting.
  • First timed mock coding interview with a human or an AI interviewer. Record it.

Exit criteria: you can go from problem statement → correct recurrence → working bottom-up DP in 25 minutes for a standard medium.