🧩 Data Structures & Algorithms

The heart of placement coding rounds. Every example is in Python, and you can run each one here.

1. Big O: measuring speed
How to say how an algorithm grows as its input grows.
2. Arrays and two pointers
Two techniques that solve many array questions in O(n).
3. Stacks and queues
Last in first out, first in first out, and a favourite interview question.
4. Linked lists
Nodes joined by links, and how to reverse one.
5. Hash maps
Average O(1) lookup, the most useful tool in coding rounds.
6. Searching and sorting
Binary search and merge sort, written out.
7. Recursion and trees
Functions that call themselves, and how to walk a binary tree.
8. Graphs: BFS and DFS
Model connections, then explore them level by level or path by path.
9. Dynamic programming
Save the answers to smaller problems instead of repeating them.
10. DSA quick reference
Which structure to reach for, and its cost.

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