- LeetCode 1 – Two Sum
The first problem on LeetCode, and still the most common phone-screen warm-up. It is not a test of whether you can find two numbers — it is a test of whether you reach for a hash map the moment you catch yourself writing a nested loop. One pass, look up before you insert, and the target = 2 × nums[i] case that lets an element pair with itself. Java and Python, plus the sorted two-pointer variant that 3Sum is built on.
- System Design – Where to Start
What system design actually is, why the question has no single right answer, and the four-step framework that keeps an hour from wandering: scope the requirements, estimate the load, sketch a high-level design, then go deep on the part that matters. What an interviewer is really scoring, the mistakes that sink candidates who know the material, and how the rest of this track is ordered.
- Elasticsearch – What to Do Before You Go to Production
The list, in the order it bites. Shard sizing and why more shards is usually the wrong instinct, replicas and what green actually promises, JVM heap and the 50% rule, security beyond turning it on — an API key scoped to one index rather than the elastic superuser every guide leaves you using — index lifecycle management, what to monitor, and the failure modes to rehearse before they happen.
- Elasticsearch – Snapshots, Restores and SLM
Registering a repository, taking a snapshot, restoring it, and automating the whole thing with a lifecycle policy — plus the retention setting that stops a cluster which was off for a month from deleting every backup it has the moment it comes back. And an honest answer to the question underneath: if your index is derived from a database, a rebuild may be the better restore, and knowing which is the point.
- Elasticsearch – The _cat APIs and Reading Cluster Health
The APIs you actually type when something is wrong. _cat/health, indices, nodes, shards and allocation, with the v, h and s parameters that make them readable. Then the questions they answer: what yellow really means and why a single-node cluster is yellow by default, which shard is unassigned and why, where the disk went, and how to tell a slow query from a slow cluster.