Features
Free, text-first and visual, with no login. See the Plans.
150-problem roadmap
An interactive map of all 150 problems with a lesson per topic, a three-level hint ladder, a tested Go solution for each, and a study plan with a calendar download.
Open the roadmapPattern lessons
21 patterns explained from first principles. Every template line says why it exists, with signals, common mistakes and tested Go code.
Browse patternsVisualizers
Step through a pattern solving a real problem, such as sliding window on Longest Substring Without Repeating Characters.
See them in the lessonsRecognition drills
114 unlabeled problems. You pick the pattern first, then see why. Optional AI feedback on your reasoning.
Try a drillDecision flowchart
Answer a few questions about a problem and get the pattern to try first.
Use the flowchartSpaced review and re-tests
Weak patterns and solved problems come back on a 3, 7, 14 and 30 day schedule.
Review todayMock interviews
A random problem, a timer and a self-review checklist, plus a re-test mode for problems you solved.
Start a mockSystem design
15 guides: an interview framework, building blocks and case studies with "what if?" follow-ups, bridged to data structures.
Open system design