Questions
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1What is the average and worst-case time complexity for lookup in a Hash Table?
2What is a Hash Collision?
3What is the difference between HashMap, TreeMap, and LinkedHashMap?
4Why is the worst-case lookup O(n)? How do modern implementations avoid this? (Tree buckets)
5What are the security implications of Hash Collision attacks (HashDoS)?
6What is the Load Factor? How does it trigger a Rehash/Resize?
7What is a Bloom Filter? When is it used? (Cache penetration, Spell check)
8What is a Hash Table? What is a Key-Value pair?
9What is a Cryptographic Hash? How does it differ from a regular hash?
10How do you design a Hash Table from scratch?
11What is a Hash Function? What makes a good hash function?
12What is the significance of Equals() and GetHashCode() in C#/Java when using objects as keys?
13What is Consistent Hashing? How is it used in Distributed Systems?
14Explain Separate Chaining. (Buckets/Linked Lists)
15Explain Open Addressing. (Linear Probing, Quadratic Probing, Double Hashing)
16Why can't we use a Hash Table efficiently for Ordered operations (e.g., find min/max)?
17Why is it bad to use a mutable object as a key in a HashMap?
Data-StructuresData-Structures
Basics
Complexity Analysis
Arrays and Strings
Linked Lists
Stacks and Queues
Hash Tables
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What is the difference between HashMap, TreeMap, and LinkedHashMap?

HashMap vs TreeMap vs LinkedHashMap

javascript
  1. 1

    HashMap: expected O(1) get/put; no general sorted iteration guarantee.

  2. 2

    LinkedHashMap: expected O(1) get/put; maintains insertion order, and can also be configured for access order.

  3. 3

    TreeMap: O(log n) get/put/remove; maintains keys in sorted order.

  4. 4

    HashMap is usually preferred for pure key-based lookup.

  5. 5

    TreeMap is appropriate for range queries, sorted traversal, and predecessor/successor operations.

  6. 6

    LinkedHashMap is useful when deterministic iteration order is required.

Difficulty: 4/10

Follow-up Questions

  • ❓How does LinkedHashMap maintain insertion order?
  • ❓When would you choose TreeMap?
  • ❓What are the memory trade-offs?