- AWS – ECS: Running Containers Without Kubernetes
ECS in the three nouns it actually has — task definition, service, cluster — and why Fargate means you never touch an EC2 instance again. A task definition for the StayHub API, the service that keeps two of them running behind a load balancer, and rolling deploys with circuit breaker rollback. Plus the two things that make a task die on startup with no useful log: the execution role and the log group.
- Oracle Database – Introduction
Oracle Database is what you meet the moment you work on anything old and important. Instance versus database, the tablespace-to-block storage hierarchy, CDB and PDB, which edition to install, and a table of every place Oracle behaves differently from MySQL and Postgres — a user is a schema, an empty string is NULL, and a DATE carries a time.
- LeetCode 31 – Next Permutation
A problem you either see or you do not — no data structure, no recursion, just three passes in the right order. It starts from one observation: a descending suffix is already maximal, so the change has to reach further left than it goes. Finding the pivot, why scanning from the right finds the smallest larger value for free, and why reversing beats sorting the suffix.
- LeetCode 28 – Implement strStr()
Reimplement indexOf. The honest answer to 'do I need to write KMP?' is almost always no — the interviewer wants a clean nested loop with correct bounds, and the bounds are the entire problem. Why i <= n - m is not a typo, how it handles a too-long needle for free, why not to allocate a substring per position, and how to raise KMP without walking into it.
- Concurrency – Double Booking and Distributed Locks
Two guests, one room, the same millisecond. Why the check-then-write everyone writes first is always wrong, optimistic against pessimistic locking, the database constraints that make a race impossible rather than unlikely, idempotency keys for requests that must not run twice, and distributed locks — what they cost, how they fail, and why they belong last on the list rather than first.