✅ DSA Interview Questions & Answers – Part 1 🧠💻

1️⃣ What is a Data Structure?
A: A way to store and organize data for efficient access and modification. Examples: Array, Linked List, Stack, Queue, Tree, Graph.

2️⃣ What is the difference between Array and Linked List?
A:
⦁ Array: Fixed size, contiguous memory, fast random access (O(1)), slow insertion/deletion (O(n)).
⦁ Linked List: Dynamic size, nodes in memory connected via pointers, slower access (O(n)), fast insertion/deletion (O(1)) at head or tail.

3️⃣ What is a Stack? Give an example.
A: Stack is a linear data structure following LIFO (Last In First Out).
⦁ Operations: push, pop, peek
⦁ Example: Browser history, Undo functionality in editors.

4️⃣ What is a Queue? Difference between Queue & Stack?
A: Queue is a linear data structure following FIFO (First In First Out).
⦁ Stack: LIFO → Last element added is first to remove.
⦁ Queue: FIFO → First element added is first to remove.
⦁ Example: Print job scheduling, Task scheduling.

5️⃣ What is a Linked List? Types?
A: Linked List is a collection of nodes where each node contains data and a pointer to the next node.
⦁ Types:
⦁ Singly Linked List
⦁ Doubly Linked List
⦁ Circular Linked List

6️⃣ What is the difference between Stack and Heap memory?
A:
⦁ Stack: Stores local variables, function calls; LIFO; automatically managed; faster access.
⦁ Heap: Stores dynamic memory; managed manually or via garbage collection; slower access; flexible size.

7️⃣ What is a Hash Table?
A: A data structure that maps keys to values using a hash function for O(1) average-time access.
⦁ Example: Python dict, Java HashMap.
⦁ Collision Handling: Chaining, Open addressing.

8️⃣ What is the difference between BFS and DFS?
A:
⦁ BFS (Breadth-First Search): Level-wise traversal; uses Queue; finds shortest path in unweighted graphs.
⦁ DFS (Depth-First Search): Deep traversal using Stack/Recursion; uses less memory for sparse graphs.

9️⃣ What is a Binary Search Tree (BST)?
A: A tree where each node:
⦁ Left child < Node < Right child
⦁ Allows O(log n) search, insertion, and deletion on average.
⦁ Not necessarily balanced → worst-case O(n).

🔟 What is Time Complexity?
A: Measure of the number of operations an algorithm takes relative to input size (n).
⦁ Examples:
⦁ O(1) → Constant
⦁ O(n) → Linear
⦁ O(log n) → Logarithmic
⦁ O(n²) → Quadratic

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