Explain HashMap internals and collisions
PayPalSoftware Engineer · Technical Screen
Last updated
This interview question evaluates algorithm design, data structures, correctness, complexity, edge cases, and implementation details in a realistic interview setting. A strong answer for Explain HashMap internals and collisions states assumptions, handles edge cases, explains trade-offs, and shows how to validate the result clearly.
In Java, describe the underlying data structures used by HashMap (e.g., array of buckets, linked lists vs tree bins) and how they evolved across Java versions. Besides separate chaining, what alternative collision-resolution strategies (e.g., linear/quadratic probing, double hashing, cuckoo hashing, Robin Hood hashing) could be used, and what are their trade-offs in time/space and cache behavior?
Solution walkthrough is for members
Get the full walkthrough with reference code and complexity analysis, plus Kitty Coach at 300 messages a day. Hints, the code runner and community answers stay free.