HashMap Internal Working in Java — Deep Visual Guide
How does HashMap actually store and retrieve data? We walk through the Node[] table, hash() spread function, bucket index calculation (n-1) & hash, collision chaining, treeification at 8 nodes, and resize at 0.75 load factor — with a live interactive 16-bucket visualizer.
Why this workshop exists
SQL interviews usually circle the same core patterns: employee questions, joins, group by, having, and a few window functions when the company wants to turn up the heat. The best way to prepare is not by reading answers in isolation, but by running them against a small schema until the shapes start to feel obvious.
What to practice first
- Employee tables: headcount, salary filters, manager self-joins, department averages, and above-average earners.
- Join questions: users to orders, order items to products, posts to tags, comments to posts.
- Advanced questions: top row per group, running totals, cumulative views, and revenue share.
The SQL Workshop on this site now includes more than 100 prompts across HR, e-commerce, and blog datasets, split into easy, medium, and hard so you can warm up properly before jumping into ranking and reporting questions.
Open the SQL Workshop and start with the HR pack if you want the most interview-like practice path.