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Watch your own code run, one line at a time
Most practice sites tell you whether you passed. This one shows you what actually happened: every variable at every step, the call stack as it grows, and each array cell the moment it changes. Edit the code below and trace it again — it runs in your browser, and nothing is uploaded.
Edit anything above and press Trace it. Nothing is uploaded; this runs in your browser.
Step through your Python one line at a time — current line, variables, output and a plain-English note for each step. Runs entirely in your browser; the first run downloads the Python runtime once (~10 MB).
This is one page of DSA Tracker, which orders 370 interview problems by the job you are actually applying for. Start with the 75 all three sheets agree on.
Why stepping through beats re-reading
“I solved it, then two weeks later I could not remember the approach” is the single most common complaint in interview prep, and it is usually diagnosed as a memory problem. It is more often a modelling problem: the solution was copied before it was understood, so there was never a mental model to forget.
Watching a loop mutate a hash map, or a recursive call pile onto the stack and unwind, builds the thing re-reading an editorial cannot. That is why this is a tracer for yourcode and not an animation of someone else’s.