How would you implement a HashMap from scratch?
This question requires you to demonstrate deep understanding of hash functions, collision resolution, and dynamic resizing mechanisms underlying key-value storage systems.
Why Interviewers Ask This
Implementing a HashMap shows you understand the internals of widely used data structures rather than just using library functions. It reveals your knowledge of hashing strategies, collision handling techniques like chaining or open addressing, and performance trade-offs. This is crucial for roles requiring optimization or custom data structure design.
How to Answer This Question
Outline the core components: an array of buckets and a hash function. Explain how keys are mapped to indices. Detail your strategy for handling collisions, such as linked lists or probing. Discuss load factor and the need for rehashing when capacity is exceeded. Mention average case O(1) retrieval and worst-case scenarios.
Key Points to Cover
- Hash function design
- Collision resolution methods
- Dynamic resizing strategy
- Load factor management
Sample Answer
I would implement a HashMap using an array of buckets where each bucket stores a list of key-value pairs. A hash function converts keys into integer indices. When inserting, I compute the hash and place the entry in the…
Common Mistakes to Avoid
- Poor hash function leading to clustering
- Forgetting to handle null keys
- Ignoring resizing triggers
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