See every algorithm run, one step at a time
Short animations you control, with the code highlighted line by line, in C# or Python. Built for interview prep, from your first array to graphs, OOP and async.
- animated lessons
- practice problems
- concept notes
- AI interview topics
- Pick a topicFollow the path below or search for what you need.
- Watch it runPlay, pause or step. Try your own input.
- Check yourselfTick topics off, then practise in an AI mock interview.
New here? Start with these six
The gentlest lessons, in order. About five minutes each.
The full path
Five stages, from fundamentals to the language itself. Jump in anywhere.
Beyond the animations
What product-company interviews ask besides writing the algorithm.
Ready to test yourself?
Ten random questions in ten minutes, on DSA, C#, OOP or CS fundamentals. Every answer is explained at the end.
Reading the code
Types the lessons share
Conventions
- Switch between C# and Python at the top of the page. C# snippets compile on .NET 8 with
System,System.Collections.GenericandSystem.Linqimported. Python snippets are Python 3.10+ with type hints. - Lessons about the C# language itself (and C#-specific features such as overloading and
newvsoverride) are shown in C# only. - Swaps use tuple syntax:
(a[i], a[j]) = (a[j], a[i])in C#,a[i], a[j] = a[j], a[i]in Python. mid = lo + (hi - lo) / 2is used instead of(lo + hi) / 2so the sum cannot overflowint. Python ints never overflow, so the Python code uses(lo + hi) // 2.- Each lesson has an "In .NET" box naming the built-in type or method that does the same job in real code.
Problem sheet
The classic interview problems, grouped by pattern. Each one has the key idea, the target complexity, a link to the matching visual lesson and a link to practise it on LeetCode.
Core concepts for product companies
Build a strong interview foundation across architecture, low-level design, databases, operating systems, networking and .NET. Start with the guided System Design path, then explore concise reference notes.
System design
Learn to turn product requirements into scalable services. Explore guided architecture diagrams, request flows, data choices, failure modes, and the tradeoffs interviewers expect you to explain.
AI mock interview
A five-question written interview. Answer in your own words as you would out loud; the AI interviewer grades each answer, shows what was missing and a strong answer, then gives you a final report.
Quick practice
Answer a random set of 12 short questions. Pick C# or Python, then a topic or All. Choose Shuffle questions for a fresh set, or finish the round to get another.
Solve problems in DSA Visual
Choose a problem, write C#, then run the sample or submit against the public test cases. Your code and progress stay in this browser.