Part of the Computer Science, Refreshed track · course 1 of 3
Data Structures & Algorithms
An interview-ready refresher on the data structures and algorithmic patterns that show up in real systems and real screens. You will reason about complexity, reach for the right structure, and recognize the handful of patterns that solve most problems. Every lesson ends with a runnable JavaScript challenge that actually executes the algorithm.
5 lessons · ~2 hours
Try the first lesson free, no account needed
Big-O & complexity. The rest of the course unlocks with a free account.
1. Core Patterns
Big-O & complexity
How to reason about how an algorithm's cost grows, and why a faster structure beats a faster loop.
Hash maps & frequency
The hash map is the universal interview tool for counting, lookups, and dedupe in one pass.
Two pointers & sliding window
Two patterns that turn nested loops over arrays and strings into a single linear pass.
Stacks & queues
Two ordering disciplines, last-in-first-out and first-in-first-out, and the problems each one solves.
Trees & graph traversal
Breadth-first versus depth-first traversal, how to represent a graph, and when each search fits.