Questions
14 of 17
Explain Separate Chaining. (Buckets/Linked Lists)
Difficulty: 5/10
collision resolution, hash tables, linked lists
Separate Chaining
Separate chaining resolves collisions by allowing each Hash Table bucket to contain multiple entries. The bucket can be implemented using a linked list, dynamic structure, or, in some modern implementations, a balanced tree when the chain becomes sufficiently large.
javascript
- 1
Multiple keys can occupy the same bucket.
- 2
Collision entries are linked or otherwise grouped together.
- 3
Average lookup remains close to O(1) when the load factor is controlled.
- 4
Worst-case lookup can become O(n) if many keys fall into one bucket.
- 5
Separate chaining makes deletion simpler than many open-addressing designs.
- 6
Modern implementations may treeify heavily populated buckets.
Scenario Questions
0-2 years experience
- 1If you need to implement a hash map for storing usernames, how would you handle collisions using separate chaining?
- 2What happens when you insert a key that hashes to a bucket that already contains a linked list of entries? Walk me through the steps.
2-5 years experience
- 1We have a service that uses a hash table with separate chaining, and after a traffic spike we notice lookups are slower. What could be causing the slowdown and how would you investigate?
- 2Suppose we need to support delete operations in a hash table that uses separate chaining. How would you implement delete, and what edge cases must you watch out for?
5-8 years experience
- 1Design a thread‑safe hash map for a high‑throughput caching layer that uses separate chaining. What synchronization strategy would you choose and why?
- 2If the average chain length grows to 10 because the load factor is high, what redesign options do you consider to keep performance predictable at scale?
8+ years experience
- 1Our legacy system uses a custom hash table with separate chaining and is being migrated to a distributed key‑value store. How would you plan the migration to minimize downtime and ensure data consistency?
- 2Across multiple services, some teams prefer open addressing while others use separate chaining. How would you evaluate the long‑term maintainability and performance trade‑offs to set a company‑wide standard?
Follow-up Questions
- Can you compare the memory overhead of separate chaining versus open addressing?
- How does the choice of linked‑list implementation affect cache locality?
- What would you do if the hash function degrades and many keys collide?