See algorithms. Build intuition.
Step through 382 data structure and algorithm topics one decision at a time. The player stops and asks what happens next before it shows you, so you cannot passively watch it.
Every lesson free, with your own input. No account needed to learn. The same engine as the iOS and Android apps, running in your browser.
16 is smaller than 56, so 56 can only be to the right. Discard 5 values.
Predict Middle value is 16 and the target is 56. What happens next?
Drawn from the engine's own trace of binary-search, not an illustration. Open the lesson, or jump to this step.
One loop, on every topic
Watch
Every step is one meaningful change: a comparison, a swap, a pointer move, a node linked. Scrub back and forth; nothing is hidden inside an animation.
Predict
At each decision the player freezes and asks what happens next. Answer, then see. Retrieval practice is the one thing in learning science with a large, replicated effect on memory.
Understand
The code line, the variables and the picture are locked to the same step. Hover a variable and its cell lights up. The explanation says why, not just what.
382 topics, 29 categories, all interactive
102 lessons, each with worked examples and a predict-mode trace. Counts come from the curriculum registry, not from marketing.
- Data Structures62
- Dynamic Programming27
- Tree Algorithms26
- Problem-Solving Patterns20
- Linked List Algorithms18
- Stack and Queue Algorithms17
- Complexity Analysis17
- Array Algorithms and Techniques15
- Sorting15
- Mathematics15
- String Algorithms13
- Bit Manipulation13
- Computational Geometry13
- Backtracking10
- Graph Traversal9
- Heap Algorithms8
- Connectivity and Topological Order8
- Greedy8
- Two Pointers8
- Algorithmic Paradigms8
- Recursion7
- Sliding Window7
- Range Queries7
- Searching6
- Shortest Path6
- Network Flow6
- Hashing5
- Divide and Conquer5
- Minimum Spanning Tree3
Not sure where to start? Two ordered tracks cross the categories in an order you can follow from nothing, one screen at a time.
Your code, through the same lens
Every lesson already runs on your own input, in your browser, on the same engine as the apps. Next, the player meets your own implementation, in this order; each step is only possible because of the one before it.
- Run yours. Paste Python or JavaScript; it runs in your browser against the lesson's cases, including the empty and single-element edges. Free
- Step through yours. Your code drives the same visualization, step by step, with predict mode on your own branches. Pro
- Diff against the reference. Where your trace first diverges, and how many more comparisons or swaps it took. Pro
- Readiness. A score per topic from your prediction accuracy, a plan against your interview date, and the review queue of what you got wrong. Pro