Beginner's guide
How to learn DSA from scratch
Data structures and algorithms (DSA) are how you organise data and solve problems with code efficiently. They're what coding interviews test. You can learn them from zero in seven steps, and every step below is free on this site, no sign-up needed.
Pick one language and stick with it
Python is the easiest to start with: short code, no boilerplate, and it's accepted in almost every interview. Java or C++ are just as good if your college or job uses them. What matters is choosing one and not switching. You need variables, loops, conditions, functions, lists and dictionaries; nothing more to begin.Watch a crash course and start →Write your first programs
Before any data structure, make loops and conditions feel automatic. The 20 coding basics (even or odd, FizzBuzz, factorial, reverse a number, prime check…) each teach one idea and run with tests in your browser. Skip this step if you can already write these without looking anything up.Start the 20 coding basics →Warm up on arrays and strings
Almost every interview problem walks an array or builds a string. The 24 warm-ups (largest element, reverse, rotate, move zeros, count characters…) are the must-know moves. Know some already? A 25-minute quick check tells you whether to skip ahead.Do the warm-ups →Learn Big O, just enough
Big O is how you compare two solutions: does the work grow with the input, or with its square? You don't need proofs, only to recognise O(1), O(log n), O(n), O(n log n) and O(n²) in your own loops.What Big O actually measures →Follow the topics in order
Each topic builds on the one before, so the order matters more than the speed. For every level: learn the concept, watch the lesson, then solve its problems from Easy to Medium.Open the DSA roadmap →Practise the way that sticks
Try each problem on your own for 20–30 minutes before looking at anything. Stuck? Take one hint, not the answer. After solving, name the pattern and the clue that pointed to it, then solve it again a day, a week and a month later. Fewer problems done this way beat hundreds skimmed.See the 159 problems in order →Then prepare for interviews
Once the levels feel comfortable, work through LeetCode 75, look up the questions your target companies ask, and do timed mock interviews where you explain your thinking out loud.Interview prep →
What's included, free
- 44 basics with tests, hints and solutions
- 13 levels from arrays to dynamic programming
- 40 concept lessons explained from scratch
- 159 hand-picked problems, in order
- 223+ walkthrough videos
- Solutions in Python, Java and C++
Common questions
- Can I learn DSA without knowing how to code?
- Yes, but learn the coding basics first. DSA is about solving problems with code, so loops and conditions need to come easily. That's what the coding basics are for.
- Which language is best for DSA?
- Python for most beginners, because the code is short and readable. Java and C++ are equally good for interviews. Every basic and problem here has solutions in all three.
- How long does it take to learn DSA?
- It depends on where you start and how much you practise. With about an hour a day, beginners typically get through the basics in a few weeks and the core topics in a few months. Practising every day matters more than long sessions.
- Do I need to be good at math?
- No. School arithmetic is enough to start. The few ideas interviews use (logarithms, modulo, sums) are explained in the math lessons when you need them.
- Is it really free?
- Yes. Every lesson, video, problem, solution and tool on AlgoChronicle is free, with no paywall and no trial. You don't even need an account; a free one only syncs your progress across devices.
- Do I need LeetCode Premium?
- No. LeetCode 75 needs no Premium, and every problem here comes with its walkthrough and solutions for free.