computer science / algorithms
Learn Algorithms & Data Structures for Free
The core of computer science — and the thing coding interviews are really testing. Here are the best free courses to actually understand algorithms, where to practice until they're second nature, and how to study them without burning out.
Algorithms are recipes for solving problems efficiently, and data structures are how you organize information so those recipes run fast. This pairing is the backbone of computer science, and mastering it does two things at once: you write noticeably better software, and you pass technical interviews, which are mostly algorithm puzzles in disguise. It's also the area beginners most often study the wrong way — grinding random problems before they understand the underlying patterns. The winning approach is simple to state: learn the concepts from a great course, then practice them on real problems by pattern until they click, and use visualizations when something won't stick. This guide gives you the best free courses for each of those steps, plus how to sequence them.
01 · LEARN
University algorithms courses
Rigorous, free courses from the schools (and professors) who literally wrote the textbooks.
- MIT 6.006 — Introduction to Algorithms ↗MIT's full course on OpenCourseWare — lecture videos, notes, and problem sets, completely free.ocw.mit.edu
- Algorithms, Part I — Princeton (Sedgewick) ↗Robert Sedgewick's classic, beautifully-taught course. Audit it free on Coursera.coursera.org
- Stanford Algorithms Specialization (Roughgarden) ↗Tim Roughgarden's renowned four-course series on algorithmic thinking. Free to audit.coursera.org
02 · PRACTICE
Practice & interview prep
Knowing algorithms isn't enough. You need reps. These teach the patterns interviewers ask for.
03 · VISUALIZE
See algorithms in motion
Some things only click when you watch them run. These make the abstract concrete.
- VisuAlgo ↗Free, interactive visualizations of data structures and algorithms — watch sorting, trees, and graphs animate step by step.visualgo.net
- The Algorithms (open-source implementations) ↗Clean, readable implementations of virtually every algorithm in dozens of languages — a superb reference.github.com/TheAlgorithms
04 · HOW TO LEARN IT
How to study algorithms without burning out
The order matters more than the hours. Learn the fundamental data structures first (arrays, hash maps, linked lists, trees, graphs) and when to use each — most problems are really asking "which structure makes this easy?" Then practice by pattern (two pointers, sliding window, breadth-first search, dynamic programming), not by grinding random problems, because the patterns are what transfer to problems you've never seen.
05 · FAQ
Frequently asked questions
What is the best free course to learn algorithms?
MIT's 6.006 Introduction to Algorithms and Princeton's Algorithms course by Robert Sedgewick are two of the best free options, both rigorous and beginner-accessible. For interview-focused practice, NeetCode's free roadmap is widely recommended alongside them.
Do I need to know algorithms for coding interviews?
Yes. Technical interviews at most software companies are largely built on data structures and algorithms, so understanding them and practicing common patterns is essential. Learning them also makes you a genuinely better engineer beyond interviews.
What should I learn first, data structures or algorithms?
Learn the core data structures first, since algorithms operate on them and most problems come down to choosing the right structure. Once you know arrays, hash maps, trees, and graphs, the algorithms that use them are much easier to understand.
How long does it take to get good at algorithms?
With consistent, pattern-focused practice, most people reach solid interview readiness in about two to three months. Deep mastery for competitive programming or advanced work takes longer, but everyday algorithmic skill is achievable in a focused stretch.
Is LeetCode enough to learn algorithms?
LeetCode is excellent for practice but works best alongside a course that teaches the underlying concepts. Learn the fundamentals first, then use a curated list like NeetCode's on LeetCode so you practice by pattern rather than solving at random.