1. What is a Data Structure?
A data structure is a way to organize, store, and manage data efficiently so it can be accessed and modified easily. Examples: Arrays, Linked Lists, Stacks, Queues, Trees, Graphs.
2. What are the different types of data structures?
- Linear: Arrays, Linked Lists, Stacks, Queues
- Non-linear: Trees, Graphs
- Hash-based: Hash Tables, Hash Maps
- Dynamic: Heaps, Tries, Disjoint Sets
3. What is the difference between Array and Linked List?
- Array: Fixed size, index-based access (O(1)), insertion/deletion is expensive
- Linked List: Dynamic size, sequential access (O(n)), efficient insertion/deletion at any position
4. How does a Stack work?
A Stack follows LIFO (Last In, First Out) principle.
- Operations:
push() to add, pop() to remove, peek() to view top - Used in: undo mechanisms, recursion, parsing
5. What is a Queue? Difference between Queue and Deque?
A Queue follows FIFO (First In, First Out).
- Deque (Double-Ended Queue): Allows insertion/removal from both ends.
- Used in scheduling, caching, BFS traversal.
6. What is a Priority Queue?
A type of queue where each element has a priority.
- Higher priority elements are dequeued before lower ones.
- Implemented using heaps.
7. What is a Hash Table and how does it work?
A structure that maps keys to values using a hash function.
- Allows O(1) average-case lookup, insert, delete.
- Handles collisions using chaining or open addressing.
8. What is the difference between HashMap and HashSet?
- HashMap: Stores key-value pairs
- HashSet: Stores only unique keys (no values)
Both use hash tables internally.
9. What are Trees? Explain Binary Tree.
A tree is a non-linear structure with nodes connected hierarchically.
- Binary Tree: Each node has at most 2 children (left, right).
Used in hierarchical data, parsers, expression trees.
10. What is a Binary Search Tree (BST)?
A special binary tree where:
- Left child < Node < Right child
- Enables fast lookup, insert, and delete in O(log n) (average case).
Maintains sorted structure.
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