Unlimited Algorithms

Watch sorting, graphs, and trees run step by step.

Mac iPhone iPad

On the Mac App Store now. iPhone and iPad coming soon.

Pick a procedure, give it input, and watch every comparison and write. Step forward, reverse exactly, inspect the invariant, and follow every claim to its source.

Dozens of procedures, not canned animations

• Explore families of procedures: sorting and selection, graphs, strings, geometry, numbers, search trees, compression, search, heaps, hash tables, dynamic programming, chance and streams, and union-find.
• Each run is recorded by the procedure itself. The picture reads that record instead of replaying a separate animation that can drift from the code.
• Purpose-built views reveal the structure at hand: arrays, trees, graphs, tables, text tapes, points, FFT butterflies, and skip-list levels.
• Open the code pane beside the stage and keep the active line, state, and explanation together.

Control every step

• Forward and backward — every change carries the information needed to undo it, so reverse stepping is exact rather than a second run.
• Play at your pace — scrub the complete run, change speed, or break on the next comparison, write, frame, or invariant failure.
• See the cost — comparisons, swaps, writes, reads, extra memory, and depth update with the current step.
• Predict what happens next — pause before a comparison, call the result, and let the run answer.

Ask the algorithm to prove itself

• Every procedure states an invariant and checks it throughout the run, including the moments when a repair such as a tree rotation is in progress.
• The catalog explains what the procedure is for, how this implementation works, its cost, and when it is the wrong tool.
• Claims name their sources. Open the original paper, textbook lineage, or specification directly from the explanation.
• Counterexample inputs make failures visible — including what happens when an algorithm’s assumptions are deliberately broken.

Choose the question

• Start from designed input shapes, reroll the same shape, change its size, or type the data yourself.
• For compatible procedures, search for an input that drives the worst case instead of merely describing one.
• Race compatible procedures on the same input. Both sides advance on a shared comparison clock, so the comparison stays honest.

One purchase, every device