Depth-First Search problems,
and the tell.
You need to reach everything, or ask a question about a whole branch before moving on. 190 problems in the catalogue carry this tag, from first-week easy to interview hard.
Free to start. Running and submitting a solution never costs credits.
How the pattern actually works.
One mechanism, and the mistake that costs people the problem.
The tell. You need to reach everything, or ask a question about a whole branch before moving on.
The mechanism. Go as deep as you can down one path, then come back and take the next. Recursion gives you the stack for free; an explicit stack does the same without risking a stack overflow.
What goes wrong. Marking a node seen when you take it out instead of when you put it in. On a graph with cycles that is an infinite walk.
The ones asked most often.
By how often the catalogue records them being set, not by our opinion.
- Binary Tree CamerasHardasked at 8 companies
- Number of Connected Components in an Undirected GraphMediumasked at 3 companies
- Difference Between Maximum and Minimum Price SumHardasked at 2 companies
- Maximum XOR of Two Non-Overlapping SubtreesHardasked at 2 companies
- Count Nodes Equal to Average of SubtreeMediumasked at 2 companies
- Path Sum IVMediumasked at 1 companies
- Island PerimeterEasyasked at 1 companies
- Detonate the Maximum BombsMediumasked at 1 companies
- Find All Groups of FarmlandMediumasked at 1 companies
- Maximize Sum of Weights after Edge RemovalsHardasked at 1 companies
Read it, watch it, then solve it.
The order that makes a pattern stick.
Everything in the app, in one place.
Practice, interviews and the tools, all free to start. Swipe to see the rest.
DSA practice
Problems filed under the pattern that solves them, not a sheet.
352 problemsOpenCompany sets
Practise what one company actually asks, the week before the round.
463 companiesOpenCoding interview
Pick the role, write in a real editor, and answer while you type.
scored reportOpenMock interviews, spoken
You answer out loud, it follows up on what you said.
36 topicsOpenDatabase round
DBMS asked the way a panel asks it: indexes, joins, normal forms.
in Core CSOpenOOP round
Inheritance, polymorphism and the follow-up you never rehearse.
in Core CSOpenSystem design
How real systems are built, from the primitives to the AI stack.
27 chaptersOpenSQL practice
Real schemas, your query, the rows it returns, and an honest verdict.
39 questionsOpenAptitude
Quant, logical, verbal, DI and technical, timed like the real test.
280 questionsOpenOnline assessment
A clock, marks per question and hidden tests, like a company's judge.
37 papersOpenAlgorithm visualiser
Watch it run on your own input, one step at a time.
26 algorithmsOpenAI that helps, not solves
Hints one at a time, AI review before a mentor reads it.
100 free creditsOpenResume builder
Build it inside the app, next to the work you practised.
in the appOpenProgress and readiness
One score, and the axis you are weakest on.
tracked dailyOpen
Free to start: 100 AI credits when you sign up and 100 every month. Start free in the app
About depth-first search problems.
Free to start, no card.
Start practisingHow do I know a problem is a depth-first search problem?
You need to reach everything, or ask a question about a whole branch before moving on.
How many depth-first search problems should I solve?
Enough to stop needing the hint, which is usually ten to fifteen across the levels, not the whole list. The catalogue tags 190, split roughly 26 easy, 122 medium and 42 hard in the sample we show, so work up rather than across.
What goes wrong most often in depth-first search problems?
Marking a node seen when you take it out instead of when you put it in. On a graph with cycles that is an infinite walk.
Is practising by pattern better than a problem sheet?
A sheet tells you what to solve. A pattern tells you why those problems sit together, which is the part that carries over to the problem you have not seen. That is why the app files every problem under its pattern.