✅ Top DSA Interview Questions with Answers: Part-1 🧠

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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